Single-step aerosol synthesis of oxygen-deficient blue titania - Domaschke, Maximilian; Strunz, Lea; Peukert, Wolfgang (Chemical Engineering Science, 2019)
We present a novel approach for the single-step, continuous aerosol synthesis of blue, oxygen-deficient titania in a hot-wall reactor operated under reducing conditions by adding hydrogen. The precursor titanium(IV) tetraisopropoxide is evaporated in a bubbler and consecutively carried into the reactor by a nitrogen stream where it undergoes thermal decomposition. According to X-ray diffraction analysis, several reduced titania states, among them the Magneli phases Ti4O7 and Ti5O9, are formed via the intermediates anatase and rutile. By slight modifications in the reactor setup both nanoparticles in the size range from 20 to 50 nm with high surface area and well-defined spherical submicron particles of 100 to 160 nm diameter can be produced. In particular, crystallographically phase-pure Ti4O7 is formed at high reactor temperatures. The presented synthesis process is scalable and poses an attractive alternative for the multi-step synthesis of oxygen deficient titania nanoparticles that is currently done via batch-wise annealing. Such nanoparticles are attractive material in the field of photocatalysis. They can be used for both water splitting to produce hydrogen and the decomposition of organic pollutants. (C) 2019 Elsevier Ltd. All rights reserved.
CRIS-Team WoS Importer:2019-07-02

Singlet Fission for Photovoltaics with 130 % Injection Efficiency - Kunzmann, Andreas; Gruber, Marco; Casillas Pacheco, Ruben; Zirzlmeier, Johannes; Stanzel, Melanie; Peukert, Wolfgang; Tykwinski, Rik; Guldi, Dirk Michael (Angewandte Chemie International Edition, 2018)
A novel pentacene dimer (P2) and a structurally analogous monomer (P1) were synthesized for use in n-type dye-sensitized solar cells. In P2, the triplet excited states formed by the rapid, spin-allowed process singlet fission were expected to enable carrier multiplication in comparison to the slow, spin-forbidden intersystem crossing seen in P1. A meta-positioning of the two pentacenes and the carboxylate anchor were chosen in P2 to balance the intramolecular dynamics of singlet fission and electron injection. Electron injection from energetically low-lying triplet excited states of pentacene units necessitated the intrinsic and extrinsic lowering of the Fermi level of the semiconductor. Indium-zinc oxide in the presence of Li+ was found to be the optimum choice for the photoelectrodes. Efficient electron injection from the triplet excited states of P1 and P2 was found, with a carrier multiplication of nearly 130 %.
Keywords: pentacene sensitizers; singlet fission; dye-sensitized solar cells; transient absorption spectroscopy

Singulettspaltung für Photovoltaikanwendungen mit Injektionseffizienzen von bis zu 130 % - Kunzmann, Andreas; Gruber, Marco; Casillas, Ruben; Zirzlmeier, Johannes; Stanzel, Melanie; Peukert, Wolfgang; Tykwinski, Rik R.; Guldi, Dirk Michael (Angewandte Chemie, 2018)

Sintering kinetics and mechanism of vitreous nanoparticles - Kirchhof, Martin; Förster, Henning; Schmid, Hans-Joachim; Peukert, Wolfgang (Journal of Aerosol Science, 2012)
The sintering of vitreous nanoparticle doublets is investigated numerically by a volume of fluid method coupled to Hamaker summation and experimentally by a high-temperature sintering flow reactor as well as by doublet shape analysis in the transmission electron microscope. In particular, the characteristic differences between nanoparticulate and bulk sintering are studied. The sintering mechanism of vitreous nanoparticles is determined to be viscous flow with interparticle van der Waals interactions acting as additional driving force. The early stages of the nanoparticle sintering kinetics are inversely proportional to the square of the particle size, instead of an indirect proportionality to the first order of the particle size for the entire bulk process. The transition between nanoparticulate and bulk sintering is localised to primary particle diameters of approx. 200-300nm. © 2011 Elsevier Ltd.
Keywords: Nanoparticles; Silica; Sintering; Van Der Waals interactions; Viscous flow

SiO2–GeO2 Glass–Ceramic Flakes as an Anode Material for High-Performance Lithium-Ion Batteries - Esper, Julian Duane; Maußner, Felix; Romeis, Stefan; Zhuo, Ying; Barr, Maissa; Yokosawa, Tadahiro; Spiecker, Erdmann; Bachmann, Julien; Peukert, Wolfgang (Energy Technology, 2022)
The preparation of a flake-like glass–ceramic anode material comprised of SiO2 and GeO2 for Li-ion batteries (LIBs) is demonstrated. The precursor glass material is prepared via a traditional melt quenching technique. Flake-like glass particles are obtained by compression in the liquid phase via ball milling. A subsequent heat treatment induces crystallization of GexSiyO6 domains inside the vitreous SiO2–GeO2 matrix. This novel glass-ceramic material is applied as an anode material for LIBs and shows a stable reversible capacity of 520 mAh g−1 at 0.2 C combined with good capacity retention of 87% after 100 cycles. This cycling stability can be attributed to the synergistic effects of having nanocrystalline domains embedded in the glass matrix: The open glass network can withstand the volume change and stress caused by the lithium insertion during cycling, while the nanocrystals act as active sites for the electrochemical conversion and alloying reactions. The glass–ceramic anode material exhibits superior electrochemical properties compared to its pure glass counterparts.
CRIS-Team Scopus Importer:2022-06-10
Keywords: anodes; flake-like particles; glass ceramics; lithium-ion batteries; shape-anisotropy; thermal annealing

Size and shape engineering of ZnO nanoparticles - Klupp Taylor, Robin; Voigt, Michael; Segets, Doris; Peukert, Wolfgang; Marczak, Renata (2008 AIChE Annual Meeting, 2008)
The investigation of ZnO nanoparticles is of great interest due to the wide range of potential applications for this material. Despite this, a thorough understanding of the optical, electronic and structural properties of ZnO nanoparticles with respect to their synthesis is still lacking. We tackled this problem by synthesizing ZnO nanoparticles with nanocrystal, nanorod and self-assembled aggregate form using ambient and hydrothermal wet chemical processes. Dynamic light scattering, absorption and emission spectroscopies, thermogravimetric analysis, X-ray powder diffraction, Fourier infrared spectroscopy as well as transmission and scanning electron microscopies were employed to characterize and compare the nanoparticles composition, their shape, size and crystallinity. By varying different parameters of the synthesis processes like precursors and their concentrations, solvent used, surfactant, temperature, and reaction time we were able to control the size and shape of the particles. In particular we noted the tendency of ZnO nanocrystals to self-assemble into dense structures which preserve the anisotropic crystal structure. Using surface-mediating polymers such as PVP, this self-organisation could be modified so as to produce nanostructures with a tunable porosity, with great potential for application.
Keywords: ZnO; nanoparticle; nanostructure; growth; crystal; self-assembly

Size-dependent nanoscale soldering of polystyrene colloidal crystals by supercritical fluids - Varghese, Jeena; Mohammadi, Reza; Pochylski, Mikolaj; Babacic, Visnja; Gapinski, Jacek; Vogel, Nicolas; Butt, Hans Juergen; Fytas, George; Graczykowski, Bartlomiej (Journal of Colloid and Interface Science, 2023)
Hypothesis: Polymer particles self-assembled into colloidal crystals have exciting applications in photonics, phononics, templates for nanolithography, and coatings. Cold soldering utilizing polymer plasticization by supercritical fluids enables a novel, low-cost, low-effort, chemical-free means for uniform mechanical strengthening of fragile polymer colloidal crystals at moderate temperatures. Here, we aim to elucidate the role of particle size and gas-specific response for the most efficient soldering, exploring the full potential of this method. Experiments: We investigate the elastic properties of polystyrene colloidal crystals made of nanoparticles with different diameters (143 to 830 nm) upon treatment with supercritical Ar and He at room temperature. By employing Brillouin light scattering, we quantify the effect of nanoparticle size on the strengthening of interparticle contacts, evaluating the permanent change in the effective elastic modulus upon cold soldering. Findings: The relative change in the effective elastic modulus reveals nonmonotonic dependence on the particle size with the most efficient soldering for mid-sized nanoparticles (about 610 nm diameter). We attribute this behavior to the crucial role of intrinsic fabrication impurities, which reduces the nanoparticles’ free surface exposed to plasticization by supercritical fluids. Supercritical Ar, a good solvent for polystyrene, enabled effective soldering of nanoparticles, whereas high-pressure He treatment is entirely reversible.
CRIS-Team Scopus Importer:2023-01-13
Keywords: Brillouin light scattering; Colloidal crystals; Mechanical and interfacial properties; Polystyrene nanoparticles; Supercritical fluids

Size effects in MgO cube dissolution - Baumann, Stefan O.; Schneider, Johannes; Sternig, Andreas; Thomele, Daniel; Stankic, Slavica; Berger, Thomas; Gronbeck, Henrik; Diwald, Oliver (Langmuir, 2015)
Stability parameters and dissolution behavior of engineered nanomaterials in aqueous systems are critical to assess their functionality and fate under environmental conditions. Using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, we investigated the stability of cubic MgO particles in water. MgO dissolution proceeding via water dissociation at the oxide surface, disintegration of Mg2+–O2– surface elements, and their subsequent solvation ultimately leads to precipitation of Mg(OH)2 nanosheets. At a pH ≥ 10, MgO nanocubes with a size distribution below 10 nm quantitatively dissolve within few minutes and convert into Mg(OH)2 nanosheets. This effect is different from MgO cubes originating from magnesium combustion in air. With a size distribution in the range 10 nm ≤ d ≤ 1000 nm they dissolve with a significantly smaller dissolution rate in water. On these particles water induced etching generates (110) faces which, above a certain face area, dissolve at a rate equal to that of (100) planes.1 The delayed solubility of microcrystalline MgO is attributed to surface hydroxide induced self-inhibition effects occurring at the (100) and (110) microplanes. The present work underlines the importance of morphology evolution and surface faceting of engineered nanomaterials particles during their dissolutio

Size effects in the elastic deformation behavior of metallic nanoparticles - Armstrong, Patrick; Peukert, Wolfgang (Journal of Nanoparticle Research, 2012)
In this work, the results of a series of molecular statics simulations to investigate the size dependence of the elastic properties of metallic nanoparticles are presented. The per-atom stiffness tensor was calculated from the derivative of the used embedded atom method potentials and, from it, lower order elastic parameters, such as the Young's modulus or the Poisson ratio. The Young's modulus decayed up to 30 % relative to the bulk values for 2.5 nm small particles, whereas the Poisson ratio showed an increase with decreasing particle size for most materials. Particles with a diameter of 30 nm approached the continuum values to around 1 %, marking the transition to continuum theory. The size-dependent Young's modulus and several other material properties can be described by a simple algebraic function of the number of atoms per particle. By plotting the radial distribution of the local Young's modulus within particles of different size, it is shown that only the outermost 2-3 atomic layers are responsible for the size-dependent change of elastic properties. Within these layers, the average atomic stiffness was found to decay linearly and independent of the particle siz
Keywords: Size effect; Elasticity; Molecular statics; Nanoparticles; Young's modulus

Size exclusion chromatography (SEC) - Peukert, Wolfgang; Kaspereit, Malte; Hofe, Thorsten; Gromotka, Lukas (Particle Separation Techniques, 2022)
Size exclusion chromatography (SEC) is a liquid phase chromatographic technique for separating molecules, proteins, macromolecules, and nanoparticles (below 100 nm) solely according to their hydrodynamic volume in solution. Classification depends on the size- and shape-dependent exclusion of components in the pores of the stationary phase material, that is, larger and less mobile components leave the column first. Ideally, the separation is purely driven by entropy, the absence of strong enthalpic interactions encompasses mild operating conditions. SEC is a standard method in polymer science and technology for the characterization of molecular weight distributions. SEC is also well established for preparative applications, for example, for the separation of proteins from aggregates in biotechnology. The size-dependent classification of nanoparticles is a promising new field of application.<br

Size specific energy (SSE) - Energy required to generate minus 75 micron material - Ballantyne, Grant; Peukert, Wolfgang; Powell, Malcolm (International Journal of Mineral Processing, 2015)
This paper explores the relationship between energy and the generation of minus 75 micron material. Rittinger's law of comminution states that the energy input is proportional to the generation of new surface area. An accurate and consistent measurement of surface area, applicable across multiple size ranges, is required to apply this practically. The amount of new - 75 μm material generated has previously been proposed as a proxy for surface area. This has been demonstrated to some extent on a range of different laboratory equipment, but not in a manner suited to equipment-independent ore characterisation. To this end the JK Rotary Breakage Tester (JKRBT) and Schönert breakage device have been used to measure the progressive production of fines from cumulative single impacts starting with 37.5 mm particles down to 250 μm. As per expectation, the generation of - 75 μm material was found to be proportional to the specific energy, but there was a secondary influence of size. A model was developed to describe the breakage and it was found that the standard t relationship could be used to effectively calculate the size specific energy. Measuring the intrinsic competence of an ore in this way can then be used to assess the energy efficiency of full-scale mills in relation to a lab scale test. It is envisaged that this relationship also has the potential to be used in the design of new comminution circuits. The methodology and the results from its application are presented for discussion and revie
Keywords: Benchmarking; Comminution; Efficiency; Energy

Smart Optical Composite Materials: Dispersions of Metal-Organic Framework@Superparamagnetic Microrods for Switchable Isotropic-Anisotropic Optical Properties - Mandel, Karl; Granath, Tim; Wehner, Tobias; Rey, Marcel; Stracke, Werner; Vogel, Nicolas; Sextl, Gerhard; Mueller-Buschbaum, Klaus (Acs Nano, 2017)
A smart optical composite material with dynamic isotropic and anisotropic optical properties by combination of luminescence and high reflectivity was developed. This combination enables switching between luminescence and angle-dependent reflectivity by changing the applied wavelength of light. The composite is formed as anisotropic core/shell particles by coating superparamagnetic iron oxide-silica microrods with a layer of the luminescent metal-organic framework (MOF) 3ınfty[Eu2(BDC)3]·2DMF·2H2O (BDC2- = 1,4-benzenedicarboxylate). The composite particles can be rotated by an external magnet. Their anisotropic shape causes changes in the reflectivity and diffraction of light depending on the orientation of the composite particle. These rotation-dependent optical properties are complemented by an isotropic luminescence resulting from the MOF shell. If illuminated by UV light, the particles exhibit isotropic luminescence while the same sample shows anisotropic optical properties when illuminated with visible light. In addition to direct switching, the optical properties can be tailored continuously between isotropic red emission and anisotropic reflection of light if the illuminating light is tuned through fractions of both UV and visible light. The integration and control of light emission modes within a homogeneous particle dispersion marks a smart optical material, addressing fundamental directions for research on switchable multifunctional materials. The material can function as an optic compass or could be used as an optic shutter that can be switched by a magnetic field, e.g., for an intensity control for waveguides in the visible range.
Keywords: anisotropy; composites; isotropy; magnetic actuation; metal organic frameworks; optical properties; smart materials; superparamagnetism; switching

Smart silver nanoparticles from nanoreactors made by invertible polyesters - Kohut, Ananiy; Voronov, Andriy; Peukert, Wolfgang (2, 2007)
We developed a simple way to prepare smart silver nanoparticles that are well dispersible in both polar and nonpolar media. The synthesis was performed using solutions of an invertible amphiphilic polyester made via a polycondensation reaction of sebacic acid and poly(ethylene glycol). Reduction, formation of silver nanoparticles, and their stabilization occur in the polyester micellar domains (nanoreactors) that are formed in the reaction medium. Comparison of XRD experimental data shows that microphase separation of polyester units resulting in subsequent large range ordering occurs by change of the polyester concentration. The shape and size of the domains depend on the polyester concentration and the ratio between the lipophilic and hydrophilic constituents in the macromolecule as well as on solvent (reaction medium) polarit
Keywords: Smart nanoparticles; Polymeric nanoreactors

Soft Particles at Liquid Interfaces: From Molecular Particle Architecture to Collective Phase Behavior. - Ciarella, Simone; Rey, Marcel; Harrer, Johannes; Holstein, Nicolas; Ickler, Maret; Löwen, Hartmut; Vogel, Nicolas; Janssen, Liesbeth M. C. (Langmuir, 2021)
-isopropylacrylamide) particle systems using phase-contrast atomic force microscopy and correlate the distinct interfacial morphology with their bulk molecular architecture. We subsequently introduce a new coarse-grained simulation method that uses augmented potentials to translate this interfacial morphology into the resulting phase behavior upon compression. The main novelty of this method is the possibility to efficiently encode multibody interactions, the effects of which are key to distinguishing between heterostructural (anisotropic collapse) and isostructural (isotropic collapse) phase transitions. Our approach allows us to qualitatively resolve existing discrepancies between experiments and simulations. Notably, we demonstrate the first in silico account of the two-dimensional isostructural transition, which is frequently found in experiments but elusive in simulations. In addition, we provide the first experimental demonstration of a heterostructural transition to a chain phase in a single-component system, which has been theoretically predicted decades ago. Overall, our multiscale framework provides a phenomenological bridge between physicochemical soft-particle characteristics at the molecular scale and nanoscale and the collective self-assembly phenomenology at the macroscale, serving as a stepping stone toward an ultimately more quantitative and predictive design approach.

Solar Light and Dopant-Induced Recombination Effects: Photoactive Nitrogen in TiO2 as a Case Study - D'Arienzo, Massimiliano; Siedl, Nicolas; Sternig, Andreas; Scotti, Roberto; Morazzoni, Franca; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2010)
The spectral response of newly synthesized and doped TiO_2 nanostructures, which are designed for the operation under solar light, is key to their potential performance as photocatalyst materials. In the case of nitrogen-doped TiO_2 particles, the presence of the photoactive defect can be verified via characteristic spectroscopic fingerprints, such as (1) an optical absorption band above extgreekl > 400 nm, (2) paramagnetic defect states related to substitutional and interstitial nitrogen atoms, and (3) a photoluminescence emission feature that can be induced by band gap excitation. We report these spectroscopic fingerprints for hydrothermally derived and N-doped TiO_2 powder samples. On the basis of defined annealing procedures, we also found a way to eliminate the photoactive nitrogen defects and performed light-induced charge separation experiments on samples before and after dopant elimination in O_2 atmosphere. The concentrations of adsorbed O_2 - ions, which stand for scavenged photogenerated electrons, were determined by electron paramagnetic resonance (EPR) spectroscopy. On the basis of these data, we calculated the number of photons, which (a) were additionally utilized because of the beneficial effect of photoactive nitrogen and (b) were lost because of the dopant-induced recombination of UV light generated charge carriers. As a major result, we found for the doped materials that both effects actually compensate each other. With regard to the synthesis and characterization of doped TiO_2 systems, these findings underline the importance to include dopant-induced charge-carrier recombination effects in the evaluation of the photocatalyst's spectral response in order to reach a fair evaluation of its properties.
EAM Import::2019-03-13

Solid distribution in fluidized and fixed beds with horizontal high speed gas jets - Köninger, Benedikt; Koegl, Thilo; Hensler, Timo; Arlt, Wolfgang; Wirth, Karl-Ernst (Powder Technology, 2018)
High speed jet penetration in fluidized beds can be used for particle size control or comminution processes. Thus, particle breakage is determined by the kinetic energy of the solids and the frequency of particle-particle impacts inside the flow. Both aspects are influenced by the solid concentration inside the jets and at the boundary. For understanding the fundamental breakage mechanism, the determination of the solid distribution in those complex flows is an important contribution. In order to access the turbulent and delicate multiphase flow, a modern fast X-ray computed tomography unit was used in this work. To obtain quantitative solid concentrations, the measurement system was optimized by means of hardware filtering, exposure time and reconstruction algorithm. These methods allowed the investigation of influencing parameters like jet velocity, fluidization velocity or particle size on the solid distribution in a single jet. With the obtained experimental data, correlations for the axial and radial solid distribution were developed. In addition, the influence of multiple jet injection with a common focal point is presented.
Keywords: Horizontal secondary gas injection; Jet milling; X-ray computed tomography; Solid distribution; Visualization of flow pattern

Solids Concentration and Solids Velocity in the Wall Region of Circulating Fluidzed Beds - Wirth, Karl-Ernst; et al. (Preprints 11th Internat. Conference on Fluidized Bed Combustion, 1991)
In circulating fluidized beds, heat is transferred to the watersteam-system by wall heat exchangers. In order to understand both the heat transfer process and the erosion of the heat exchanger it is particularly interesting to know the solids concentration and the solids velocity near the wall of the circulating fluidized bed. Two systems for measuring these quantities were developed. The principle of the measurement of the solids concentration is based on the attenuation of a γ-beam passing the circulating fluidized beds. Shifting the radiation source and the detector across the cross-section of the circulating fluidized bed it was possible to measure the radial solids concentration profile. The experiments showed that the solids concentration in the wall region is about three times as large as that in the core region of the bed and that a small layer free of solids and about 1 mm thick exists immediate near the wall. This measuring system is applicable in industrial fluidized bed combusters, because no part of the systems is placed in the bed. The velocity was measured by using a phosphorescent material. A small part of this material was marked by a light flash and then traced with a video camera. We observed that all the material immediate near the wall is falling down and the velocity of this falling film is in the order of one to three meter per second.
UnivIS-Import:2015-04-16:Pub.1991.tech.ITC.mechve.solids
Keywords: fluidized; bed; combustion

Solid-Solid Interface Formation in TiO2 Nanoparticle Networks - Baumann, Stefan O.; Elser, Michael J.; Auer, Michael; Bernardi, Johannes; Huesing, Nicola; Diwald, Oliver (Langmuir, 2011)
Aiming at a comparison of microstructure and paramagnetic properties of mesoporous TiO_2 nanoparticle networks, we subjected entirely different TiO2-x precursor structures to vacuum annealing. The transformation of an amorphous TiO2-x gel—obtained by sol-gel processing of an ethylene glycol-modified titanium precursor—into a network of interconnected anatase nanocrystals was explored by means of X-ray diffraction, nitrogen sorption, and electron microscopy. Crystalline junctions between the particles emerge from temperature treatment. This process of particle network formation is different from that related to the vapor phase grown anatase nanocrystals where particle-particle interface formation is induced by contact with water. It was found that, after annealing up to 873 K and controlled sample purification in oxygen atmosphere, both types of samples exhibit high concentrations of particle-particle interfaces and comparable properties in terms of surface area, porosity, and microstructure. With electron paramagnetic resonance (EPR) we observed on nonstoichiometric TiO2-x networks an identical type of subsurface defect which is related to the presence of solid-solid interfaces.
EAM Import::2019-03-13

Solid state interdigitated Sb(2)S(3)based TiO(2)nanotube solar cells - Büttner, Pascal; Döhler, Dirk; Korenko, Sofia; Möhrlein, Sebastian; Bochmann, Sebastian; Vogel, Nicolas; Minguez Bacho, Ignacio; Bachmann, Julien (RSC Advances, 2020)
TiO(2)nanotubes generated by anodization of metallic titanium sputter-coated on indium tin oxide (ITO) substrates are used as a conductive scaffold for all solid-state Sb2S3-sensitized extremely thin absorber (ETA) solar cells. A blocking layer of TiO(2)placed between Ti and ITO in combination with optimized Ti deposition and anodization conditions enables the formation of crack-free layers of straight, cylindrical TiO(2)nanotubes of tunable length and diameter. ALD (atomic layer deposition) is subsequently used to coat this substrate conformally with a highly pure Sb(2)S(3)light absorber layer under an inert atmosphere. The high absorption coefficient of Sb(2)S(3)as compared to molecular dyes allows for the utilization of very short nanotubes, which facilitates the infiltration of the organic hole transport material and formation of a p-i-n heterojunction in an interdigitated and tunable geometry. We investigate the influence of nanotube length and of the absorber thickness to enhance the photocurrent value to twice that of planar reference structures.

Solid state interdigitated Sb(2)S(3)based TiO(2)nanotube solar cells - Büttner, Pascal; Döhler, Dirk; Korenko, Sofia; Moehrlein, Sebastian; Bochmann, Sebastian; Vogel, Nicolas; Minguez-Bacho, Ignacio; Bachmann, Julien (RSC Advances, 2020)
TiO(2)nanotubes generated by anodization of metallic titanium sputter-coated on indium tin oxide (ITO) substrates are used as a conductive scaffold for all solid-state Sb2S3-sensitized extremely thin absorber (ETA) solar cells. A blocking layer of TiO(2)placed between Ti and ITO in combination with optimized Ti deposition and anodization conditions enables the formation of crack-free layers of straight, cylindrical TiO(2)nanotubes of tunable length and diameter. ALD (atomic layer deposition) is subsequently used to coat this substrate conformally with a highly pure Sb(2)S(3)light absorber layer under an inert atmosphere. The high absorption coefficient of Sb(2)S(3)as compared to molecular dyes allows for the utilization of very short nanotubes, which facilitates the infiltration of the organic hole transport material and formation of a p-i-n heterojunction in an interdigitated and tunable geometry. We investigate the influence of nanotube length and of the absorber thickness to enhance the photocurrent value to twice that of planar reference structures.
CRIS-Team WoS Importer:2020-08-28

Solvent effects of zinc sulfide quantum dots classified by size selective precipitation - Mori, Y.; Yamamoto, K.; Segets, Doris; Peukert, Wolfgang; Tuchiya, K. (22nd International Congress of Chemical and Process Engineering (CHISA 2016) and 19th Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction (PRES 2016), 2016)

Sonochemical processing and characterization of composite materials based on soy protein and alginate containing micron-sized bioactive glass particles - Silva Lourenco, Rauqel; Bulut, Buse; Roether, Judith; Kaschta, Joachim; Schubert, Dirk W.; Boccaccini, Aldo R. (Journal of Molecular Structure, 2014)
Novel composite hydrogels based on the combination of natural polymers; namely alginate and soy protein isolate, and bioactive glass (BC) particles (mean size: 2 pm) were developed. For this purpose a sono-chemical approach was used and homogeneous composite hydrogels, incorporating two concentrations of BC particles, were successfully obtained. Further physico-chemical characterization was performed in order to evaluate the influence of each component on hydrogel properties. The water uptake ability, weight loss, protein release, as well as FTIR, SEM and DMTA characterization were carried out. The bio-mineralization process in simulated body fluid (SBF) was followed over time and the results demonstrated that the composite materials have the ability to form a surface apatite layer after 7 days in SBF. The design of novel composite hydrogels based on soy protein, alginate and BC can be a suitable approach for bone regeneration applications. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: Alginate; Soy isolate protein; Bioactive glass; Hydrogel; Tissue engineering

Spatially resolved flame zone classification of a flame spray nanoparticle synthesis process by combining different optical techniques - Kilian, Daniel; Engel, Sascha; Borsdorf, B.; Gao, Yi; Kögler, Andreas; Kobler, S.; Seeger, Thomas; Will, Stefan; Leipertz, Alfred; Peukert, Wolfgang (Journal of Aerosol Science, 2014)
Flame spray synthesis of silica nanoparticles is characterized by a set of complementary optical techniques. By means of laser-sheet based Mie scattering imaging, 2D-chemiluminescence imaging and coherent anti-Stokes Raman spectroscopy (CARS) local information on spatial droplet distribution, combustion zone, nucleation zone and temperature in the flame could be obtained. In addition, the outcomes from optical metrology are validated by thermophoretic sampling at different flame heights and the synthesized powders were analyzed by N2 gas sorption. By comparing these results the flame can be quantitatively classified into three distinct zones: (i) the droplet zone where precursor atomization and evaporation take place, (ii) the nucleation zone indicated by SiO*/Si* radicals as a preliminary species before SiO2 particle formation and (iii) the sintering zone characterized by the highest temperatures in flame. In addition the spatial spreading of the nucleation zone as a function of precursor concentration is investigated. Theoretical calculations and experimental results show an extended nucleation regime for the lowest precursor concentration compared to higher concentrations. Although this study is performed with hexamethyldisiloxane (HMDS) precursor to synthesize silica nanoparticles as a model system, dimensionless analysis shows that the results, concerning the spray formation, can be transferred to the synthesis of other materials as well.

Spatioselective Deposition of Passivating and Electrocatalytic Layers on Silicon Nanowire Arrays. - Wendisch, Fedja J.; Abazari, Mehri; Werner, Valerie; Barb, Horia; Rey, Marcel; Görlitzer, Eric; Vogel, Nicolas; Mahdavi, Hossein; Bourret, Gilles R. (ACS Applied Materials and Interfaces, 2020)
Metal–silicon nanowire array photoelectrodes provide a promising architecture for water-splitting because they can afford high catalyst loading and decouple charge separation from the light absorption process. To further improve and understand these hybrid nanowire photoelectrodes, control of the catalyst amount and location within the wire array is required. Such a level of control is currently synthetically challenging to achieve. Here, we report the synthesis of cm2-sized hybrid silicon nanowire arrays with electrocatalytically active Ni–Mo and Pt patches placed at defined vertical locations within the individual nanowires. Our method is based on a modified three-dimensional electrochemical axial lithography (3DEAL), which combines metal-assisted chemical etching (MACE) to produce Si nanowires with spatially defined SiO2 protection layers to selectively cover and uncover specific areas within the nanowire arrays. This spatioselective SiO2 passivation yields nanowire arrays with well-defined exposed Si surfaces, with feature sizes down to 100 nm in the axial direction. Subsequent electrodeposition directs the growth of the metal catalysts at the exposed silicon surfaces. As a proof of concept, we report photoelectrocatalytic activity of the deposited catalysts for the hydrogen evolution reaction on p-type Si nanowire photocathodes. This demonstrates the functionality of these hybrid metal/Si nanowire arrays patterned via 3DEAL, which paves the way for investigations of the influence of three-dimensional geometrical parameters on the conversion efficiency of nanostructured photoelectrodes interfaced with metal catalysts.
Keywords: Metals; Nanowires; Nanowire arrays; Catalysts; Deposition

Special Issue of Core-to-Core Young Researchers Meeting 2008 Preface - Peukert, Wolfgang; Higashitani, Ko; Marczak, Renata (Advanced Powder Technology, 2010)

Specific effects of Ca2+ ions and molecular structure of β-lactoglobulin interfacial layers that drive macroscopic foam stability - Braunschweig, Björn; Schulze-Zachau, Felix; Nagel, Eva; Engelhardt, Kathrin; Stoyanov, Stefan; Gochev, Georgi; Khristov, Khr.; Mileva, Elena; Exerowa, Dotchi; Miller, Reinhard; Peukert, Wolfgang (Soft Matter, 2016)
β-Lactoglobulin (BLG) adsorption layers at air–water interfaces were studied in situ with vibrational sum-frequency generation (SFG), tensiometry, surface dilatational rheology and ellipsometry as a function of bulk Ca2+ concentration. The relation between the interfacial molecular structure of adsorbed BLG and the interactions with the supporting electrolyte is additionally addressed on higher length scales along the foam hierarchy – from the ubiquitous air–water interface through thin foam films to macroscopic foam. For concentrations <1 mM, a strong decrease in SFG intensity from O–H stretching bands and a slight increase in layer thickness and surface pressure are observed. A further increase in Ca2+ concentrations above 1 mM causes an apparent change in the polarity of aromatic C–H stretching vibrations from interfacial BLG which we associate to a charge reversal at the interface. Foam film measurements show formation of common black films at Ca2+ concentrations above 1 mM due to considerable decrease of the stabilizing electrostatic disjoining pressure. These observations also correlate with a minimum in macroscopic foam stability. For concentrations >30 mM Ca2+, micrographs of foam films show clear signatures of aggregates which tend to increase the stability of foam films. Here, the interfacial layers have a higher surface dilatational elasticity. In fact, macroscopic foams formed from BLG dilutions with high Ca2+ concentrations where aggregates and interfacial layers with higher elasticity are found, showed the highest stability with much smaller bubble size

Specific Properties of Nanoparticles - Peukert, Wolfgang; Walter, Johannes (Powder Technology Handbook, Fourth Edition, 2019)

Spectra library: An assumption-free in situ method to access the kinetics of catechols binding to colloidal ZnO quantum dots - Lin, Wei; Haderlein, Michael; Walter, Johannes; Peukert, Wolfgang; Segets, Doris (Angewandte Chemie International Edition, 2016)
Assumption-free and in situ resolving of the kinetics of ligand binding to colloidal nanoparticles (NPs) with high time resolution is still a challenge in NP research. A unique concept of using spectra library and stopped-flow together with a "search best-match" Matlab algorithm to access the kinetics of ligand binding in colloidal systems is reported. Instead of deconvoluting superimposed spectra using assumptions, species absorbance contributions (ligand@ZnO NPs and ligand in solution) are obtained by offline experiments. Therefrom, a library of well-defined targets with known ligand distribution between particle surface and solution is created. Finally, the evolution of bound ligand is derived by comparing in situ spectra recorded by stopped-flow and the library spectra with the algorithm. Our concept is a widely applicable strategy for kinetic studies of ligand adsorption to colloidal NPs and a big step towards deep understanding of surface functionalization kinetics. Well-established libraries of target spectra that are derived by means of careful offline analysis and identification of equilibrium data within larger kinetic datasets can be used for any particle-ligand system. Kinetics of ligand binding to nanoparticles can be derived free of assumption, in situ, and with high time resolution.
Keywords: colloids; kinetics; ligand exchange; nanoparticles; surface analysis

Spectroscopy of Electrified Interfaces with Broadband Sum Frequency Generation: From Electrocatalysis to Protein Foams - Braunschweig, Björn; Mukherjee, Prabuddha; Kutz, Robert; Rumpel, Armin; Engelhardt, Kathrin; Peukert, Wolfgang; Dlott, Dana; Wieckowski, Andrzej (Vibrational Spectroscopy at Electrified Interfaces, 2013)
This chapter focuses on the application of vibrational sum frequency generation (SFG) spectroscopy to study the molecular structure of electrode‐electrolyte and electrified liquid‐gas interfaces. Vibrational SFG is inherently interface specific because a second‐order process such as SFG is not allowed in the bulk of materials with inversion symmetry. The development of direct ethanol fuel cells demands an in‐depth understanding of ethanol's electrooxidation reactions. With recent advances in the practical design of alkaline fuel cells, a thorough understanding of the ethanol electrooxidation mechanism in alkaline media is now more important than ever. The chapter provides novel insights into this mechanism by examining new data on surface‐adsorbed reaction intermediates at fuel cell relevant conditions. Foams are materials of particular importance since they have a broad range of applications such as metal foams for light‐weight structures, polymer foams for thermal insulation, as well as in textured food product
Keywords: Electrooxidation reactions; Ethanol fuel cells; Electrified interfaces; Electrocatalysis; Vibrational sum frequency generation (SFG); Protein foams; Spectroscopy

Spectro-Spatial Unmixing in Optical Microspectroscopy for Thickness Determination of Layered Materials - Schwarz, Julian; Niebauer, Michael; Römling, Lukas; Pham, Adrian; Kolesnik-Gray, Maria; Evanschitzky, Peter; Vogel, Nicolas; Krstic, Vojislav; Rommel, Mathias; Hutzler, Andreas (Advanced Optical Materials, 2025)
Van der Waals materials and devices incorporating them exhibit highly thickness-dependent properties. The small lateral dimensions of mechanically exfoliated 2D-layered flakes, however, remarkably complicate their precise thickness determination. Quantitative analysis of reflectance measurements using optical microspectroscopy is proven to be as precise as spectroscopic ellipsometry while providing an easily adaptable and non-destructive method for thickness determination. The use of magnifying objective lenses allows obtaining the reflectance within a measurement spot of only a few microns in diameter. When the dimensions of exfoliated flakes are even smaller, however, the acquired reflectance is a superposition of those of the material of interest and the subjacent materials. To overcome this limitation, a facile approach to reduce the resolvable structure size by combining the evaluation of the reflectance measurement via transfer matrix method with spatial information extracted from optical micrographs is introduced. The efficacy when characterizing micrometer-sized flakes is exemplarily demonstrated for thickness determination of highly oriented pyrolytic graphite and a thin film of silicon dioxide. It is shown that a maximum error of less than 10% is achieved even when the flake only covers 20% of the measurement spot.
CRIS-Team Scopus Importer:2025-02-04
Keywords: 2D materials; graphite; reflectance; thin films; transfer matrix method

Spherical Polybutylene Terephtalate (PBT)-Polycarbonate (PC) Blend Particles by Mechanical Alloying and Thermal Rounding - Dechet, Maximilian; Gomez Bonilla, Juan Sebastian; Lanzl, Lydia; Drummer, Dietmar; Bück, Andreas; Schmidt, Jochen; Peukert, Wolfgang (Polymers, 2018)
In this study, the feasibility of co-grinding and the subsequent thermal rounding to produce spherical polymer blend particles for selective laser sintering (SLS) is demonstrated for polybutylene terephthalate (PBT) and polycarbonate (PC). The polymers are jointly comminuted in a planetary ball mill, and the obtained product particles are rounded in a heated downer reactor. The size distribution of PBT-PC composite particles is characterized with laser diffraction particle sizing, while the shape and morphology are investigated via scanning electron microscopy (SEM). A thorough investigation and characterization of the polymer intermixing in single particles is achieved via staining techniques and Raman microscopy. Furthermore, polarized light microscopy on thin film cuts enables the visualization of polymer mixing inside the particles. Trans-esterification between PBT and PC during the process steps is investigated via vibrational spectroscopy and differential scanning calorimetry (DSC). In this way, a new process route for the production of novel polymer blend particle systems for SLS is developed and carefully analyzed.
Keywords: polybutylene terephthalate (PBT); polycarbonate (PC); polymer blend particles; spheroidization; additive manufacturing; Raman microscopy; SEM staining; trans-esterification

SPIONs functionalized with small peptides for binding of lipopolysaccharide, a pathophysiologically relevant microbial product. - Karawacka, Weronika; Janko, Christina; Unterweger, Harald; Mühlberger, Marina; Lyer, Stefan; Taccardi, Nicola; Mokhir, Andriy; Jira, Wolfgang; Peukert, Wolfgang; Boccaccini, Aldo R.; Kolot, Mikhail; Strauss, Richard; et al. (Colloids and Surfaces B-Biointerfaces, 2018)
Systemic inflammation such as sepsis represents an acute life-threatening condition, to which often no timely remedy can be found. A promising strategy may be to functionalize magnetic nanoparticles with specific peptides, derived from the binding motives of agglutinating salivary proteins, that allow immobilization of pathogens. In this work, superparamagnetic iron oxide nanoparticles with stable polycondensed aminoalkylsilane layer were developed, to which the heterobifunctional linkers N-succinimidyl 3-(2-pyridyldithio)-propanoate (SDPD) and N-succinimidyl bromoacetate (SBA) were bound. These linkers were further chemoselectively reacted with the thiol group of singularly present cysteines of selected peptides. The resulting functional nanoparticles underwent a detailed physicochemical characterization. The biocompatibility of the primarily coated aminoalkylsilane particles was also investigated. To test the pathogen-binding efficacy of the particles, the lipopolysaccharide-immobilization capacity of the peptide-coated particles was compared with free peptides. Here, one particle-bound peptide species succeeded in capturing 90% of the toxin, whereas the degree of immobilization of the toxin with a system that varied in the sequence of the peptide dropped to 35%. With these promising results, we hope to develop extracorporeal magnetic clearance systems for removing pathogens from the human body in order to accelerate diagnosis and alleviate acute disease conditions such as sepsis.

Spontaneous Growth of Magnesium Hydroxide Fibers at Ambient Conditions - Gheisi, Amirreza; Sternig, Andreas; Rangus, Mojca; Redhammer, Günther; Hartmann, Martin; Diwald, Oliver (Crystal Growth & Design, 2014)
Spontaneous transformation paths of nanomaterials point to guiding, principles for synthesis. We describe the room temperature transformation of MgO nanocubes into Mg-3(OH)(5)Cl center dot 4H(2)O nanofibers in air and investigated the underlying formation mechanism using electron microscopy, X-ray diffraction, and solid-state NMR spectroscopy. Upon contact with water vapor, the magnesium hydroxide needles were found to grow out of agglomerates of highly dispersed MgO nanocubes with preadsorbed SiCl4. Corresponding one-dimensional nanostructures do not form on low surface area materials. The presented growth approach is potentially extendable to other hydrolyzable metal oxides at ultrafine dispersion.

Spray agglomeration of polymer particles: Influence of spray parameters on shape factors - Düsenberg, Björn; Schmidt, Jochen; Singh, Abhinandan Kumar; Bück, Andreas (Powder Technology, 2023)
This work systematically investigates the influence of spray parameters on the shape factor descriptors and the fractal dimensions of polymer agglomerates produced by fluidised bed spray agglomeration. Polystyrene primary-particles with sizes <100 μm (Geldart C/A) are used to investigate the shape formation during the agglomeration process with regard to the spray-parameters, i.e., volume flows of the atomization gas and the binder liquid. As binding agent, a solution of polymethyl-methacrylate in acetone is used. Analysis of the agglomerates is carried out using scanning electron microscopy and laser diffraction. Development of agglomerate-size and the distributions of the shape factors circularity, roundness and compactness are monitored by image analysis and correlated with the spray parameters. The calculation of the fractal dimensions with regard to the Sauter mean diameter using the box counting method is performed and compared with the shape factors, resulting in two complementary methods to describe the shape of agglomerates.
CRIS-Team Scopus Importer:2023-04-07
Keywords: Fluidized bed; Fractal dimensions; Shape factor; Spray agglomeration

Spray-Dried Photonic Balls with a Disordered/Ordered Hybrid Structure for Shear-Stress Indication - Wenderoth, Sarah; Bleyer, Gudrun; Endres, Jakob; Prieschl, Johannes; Vogel, Nicolas; Wintzheimer, Susanne; Mandel, Karl (Small, 2022)
Optical microscale shear-stress indicator particles are of interest for the in situ recording of localized forces, e.g., during 3D printing or smart skins in robotic applications. Recently developed particle systems are based on optical responses enabled by integrated organic dyes. They thus suffer from potential chemical instability and cross-sensitivities toward humidity or temperature. These drawbacks can be circumvented using photonic balls as shear-stress indicator particles, which employ structural color as the element to record forces. Here, such photonic balls are prepared from silica and iron oxide nanoparticles via the scalable and fast spray-drying technique. Process parameters to create photonic balls with a disordered core and an ordered particle structure toward the exterior of the supraparticles are reported. This hybrid disordered–ordered structure is responsible for a color loss of the indicator particles during shear-stress application because of irreversible structural destruction. By adjusting the primary silica particle sizes, nearly all colors of the visible spectrum can be achieved and the sensitivity of the response to shear stress can be adjusted.
CRIS-Team Scopus Importer:2022-10-28
Keywords: disordered/ordered core–shell structures; hybrid materials; photonic balls; shear-stress indicators; supraparticles

Spray Printing of Porous Substrates from Nanosuspensions - Panduro Vela, David; Schlumberger, Carola; Thommes, Matthias; Bück, Andreas (Processes, 2023)
In this work, we present and characterise an experimental setup that allows the generation of porous packings from nanosuspensions. By defined positioning and drying of solid-containing droplets, large-scale porous structures can be generated. Examples of such structures are shown and characterised. Operational challenges are presented, and it is discussed how they can be overcome to allow the maximum degree of freedom in packing generation.
CRIS-Team Scopus Importer:2023-05-12
Keywords: drop-on-demand; drying; porosity; suspension; textural characterization

Stability and local environment of iron in vapor phase grown MgO nanocrystals - Niedermaier, Matthias; Dolcet, Paolo; Gheisi, Amirreza; Tippelt, Gerold; Lottermoser, Werner; Gross, Silvia; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2017)
Metallocene injection into a metal combustion flame has been used for trapping transition metal ions inside MgO nanocrystals. Vacuum annealing changes the properties of resulting nonequilibrium solids toward thermodynamic equilibrium and provides means to control impurity localization and, as a result, the nanomaterials’ functional properties. By combining structure characterization (X-ray diffraction and transmission electron microscopy) with X-ray absorption spectroscopy and Mössbauer measurements, we tracked valence state and local chemical environment changes of Fe3+ ions inside vapor phase synthesized MgO nanocrystals. At a concentration of (1.5 ± 0.2) at. % Fe about (1400 ± 200) Fe3+ ions are effectively diluted within 12 nm sized nanocubes, where they form complexes between Fe3+ ions and Mg2+ vacancies. Increase of the iron concentration produces additional effects: enhanced ion diffusion and particle coarsening at elevated temperatures, clustering of Fe3+–Mg2+ vacancy complexes and, after annealing to T = 1173 K, the nucleation of a magnesioferrite phase that can be detected by X-ray diffraction for 4 at. % samples. At 3 at. % Fe, corresponding impurity ions induce surface energy changes that have a substantial impact on particle shape. With regard to the functional properties associated with transition metal ions in insulating MgO host lattices, the here presented insights underline that annealing-induced reorganization of oxide nanoparticles provides important parameters to control distribution and localization of impurity ion

Stability and Photoelectronic Properties of Layered Titanate Nanostructures - Riss, Alexander; Elser, Michael J.; Bernardi, Johannes; Diwald, Oliver (Journal of the American Chemical Society, 2009)
Layered titanate nanostructures offer promising photoelectronic properties that are subject to surface chemistry-induced morphology changes. For a systematic evaluation of the bulk and surface contributions to the photoactivity of these structures, we investigated their photoelectronic properties and in particular their dependence on the condition of the gas-solid interface. We comprehensively explored the stability of Na_2Ti_3O7 nanowires and scrolled up H_2Ti_3O7 nanotubes by means of transmission electron microscopy, Raman, and FT-IR spectroscopy and subjected both titanate sheet-based structures to controlled thermal activation treatment under high vacuum conditions. We found that throughout thermal annealing up to T = 870 K the structure and morphology of Na_2Ti_3O7 nanowires are retained. Consistent with the significant photoluminescence emission that is attributed to radiative exciton annihilation in the bulk, UV-induced charge separation is strongly suppressed in these structures. H_2Ti_3O7 nanotubes, however, undergo transformation into elongated anatase nanocrystals during annealing at temperatures T ≥ 670 K. Photoexcitation experiments in O_2 atmosphere reveal that these structures efficiently sustain the separation of photogenerated charges. Trends in the abundance of trapped holes and scavenged electrons were characterized quantitatively by tracking the concentration of paramagnetic O- and O_2- species with electron paramagnetic resonance spectroscopy EPR, respectively. An incisive analysis of these results in comparison to those obtained on airborne anatase nanocrystals underlines the critical role of surface composition and structure on charge separation and, in consequence, on the chemical utilization of photogenerated charge carriers.
EAM Import::2019-03-13

Stability, convergence, and energy preservation robust methods for fully implicit and fully explicit coupling schemes - Munir, Taj; Kang, Can; Chen, Hongchu; Zeb, Hussan; Khan, Muhammad Naveed; Farid, Muhammad Usman (Chaos Solitons & Fractals, 2025)
This paper presents an analysis of the Godunov–Ryabenkii stability, Generalized Mini-mal Residual(GMRES) convergence, and energy-preserving properties of partitioned and monolithic approaches (fully implicit and fully explicit schemes) for solving coupled parabolic problems. Specifically, we consider a bi-domain parabolic diffusion problem with two types of coupling conditions at the interface: Dirichlet–Neumann and heat-flux coupling. Our findings shows that the Dirichlet–Neumann coupling is unconditionally stable for both approaches. In contrast, the heat-flux coupling requires additional conditions to ensure the stability of the coupled problem. For numerical approximations, finite volume and finite difference schemes are used. The results show that energy preservation is achieved with one-sided differences in the finite volume method, while the finite difference method achieves conservation when central difference approximations are used for both the coupling and boundary conditions in the heat-flux coupling case. Additionally, Dirichlet–Neumann coupling maintains stability and energy preservation in both methods using the one-sided approach without requiring extra conditions. However, for heat-flux coupling, an additional restriction is necessary to ensure stability. The challenge for the convergence of coupled interface problems arise due to strong domain interactions and sensitive interface conditions, like Dirichlet–Neumann or heat-flux coupling. The poor system conditioning and discretization choices can slow the rate of convergence. For this purpose we used the GMRES method. This work provides a comprehensive framework for addressing coupled parabolic diffusion problems using robust, stable, and energy-preserving numerical methods.
CRIS-Team Scopus Importer:2025-03-14
Keywords: Conjugate heat transfer; Dirichlet–Neumann algorithms; Heat flux coupling; Stability analysis and discrete energy conservation

Stabilization mechanism of ZnO quantum dots - Peukert, Wolfgang; Marczak, Renata; Schäfer, Stefan; Segets, Doris (Nanotechnology 2010: Advanced Materials, CNTs, Particles, Films and Composites - 2010 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2010, 2010)
The current work addresses the understanding of the stabilization of small ZnO quantum dots in ethanolic suspension. Thereby different degrees of purification were investigated. The results revealed that not only the well-known ζ-potential as a representative for the surface charge determines the colloidal stability but also the surface coverage of acetate groups bound to the particle surface. Those acetate groups act as molecular spacers between the nanoparticles and prevent agglomeration. Regarding DLVO-calculations using a core-shell model, not only the height of the maximum but also the depth of the primary minimum has to be considered to see if a colloidal suspension is stable or not.
Keywords: Core-shell model; Purification; Quantum dot; Stability; ZnO

Stabilization of carbon black particles with Cetyltrimethylammoniumbromide in aqueous media - Eisermann, Claudia; Damm, Cornelia; Winzer, Bettina; Peukert, Wolfgang (Powder Technology, 2014)
The stabilization mechanism of aqueous carbon black suspensions by Cetyltrimethylammoniumbromide (CTAB) is studied in this paper. The adsorption of the surfactant CTAB on the carbon black particles was investigated on dried samples by thermogravimetric analyses (TGA), nitrogen adsorption and attenuated total reflection Fourier transformation infrared spectroscopy (ATR-FTIR) as well as in suspension by zeta potential measurements and atomic force microscopy. The particles are stabilized by an adsorbed CTAB monolayer as can be concluded from the results of TGA and of AFM investigations using a liquid cell. Extended DLVO calculations including the steric contribution of CTAB reveal that carbon particles with an adsorbed monolayer of CTAB exhibit sufficient colloidal stability. This result is in qualitative agreement with the experimental results. © 2013 Elsevier B.V.
Keywords: Carbon black; CTAB adsorption; Dispersion; DLVO calculations; Electrosteric stabilization

State Diagrams of Gas/Solid Flow with Partial Phase Separation - Wirth, Karl-Ernst; Molerus, Otto (KONA Powder and Particle Journal, 1991)
Preferable operational conditions of gas/solid flows are often situated in the transitional regime between two well defined modes, typical examples being pneumatic transport in a horizontal pipe and circulating fluidized beds. The energetic optimum of horizontal pneumatic transport is situated in the transitional regime between strand flow and fully developed flow in which regimes with different physical factors (wall friction of sliding material or single particle wall impact, respectively) prevail. The circulating fluidized bed may be regarded as the transition from a bubbling fluidized bed to pneumatic transport vertically upwards. Experimental results indicate particle slip velocities which are quite a bit higher than predicted by single particle fall velocity, hence indicating strong phase separation in terms of clusters. In both situations, empirical correlations fail because they ignore the complicated structure of the system in question, i.e. being transitional. On the other hand, even very sophisticated modelling can fail, because it is mostly based on inherent a priori assumptions concerning the state of flow. As an alternative, comparably simple models of two phase flows in horizontal pipes and for circulating fluidized beds are presented. The models originate from very obvious visual observations and from considerations of momentum exchange between the two phases. The evaluation of the respective resulting sets of algebraic equations can be represented in terms of state diagrams for gas/solid flows with partial phase separatio
UnivIS-Import:2015-03-05:Pub.1991.tech.ITC.mechve.stated_78
Keywords: gas; solid; flow; fluidization

State Diagrams of Gas/Solids Flows with Partial Phase Separation - Wirth, Karl-Ernst; Molerus, Otto (Shell Conference on Particle Technology, 1990)
Preferable operational conditions of gas/solid flows are often situated in the transitional regime between two well defined modes, typical examples being pneumatic transport in a horizontal pipe and circulating fluidized beds. The energetic optimum of horizontal pneumatic transport is situated in the transitional regime between strand flow and fully developed flow in which regimes with different physical factors (wall friction of sliding material or single particle wall impact, respectively) prevail. The circulating fluidized bed may be regarded as the transition from a bubbling fluidized bed to pneumatic transport vertically upwards. Experimental results indicate particle slip velocities which are quite a bit higher than predicted by single particle fall velocity, hence indicating strong phase separation in terms of clusters. In both situations, empirical correlations fail because they ignore the complicated structure of the system in question, i.e. being transitional. On the other hand, even very sophisticated modelling can fail, because it is mostly based on inherent a priori assumptions concerning the state of flow. As an alternative, comparably simple models of two phase flows in horizontal pipes and for circulating fluidized beds are presented. The models originate from very obvious visual observations and from considerations of momentum exchange between the two phases. The evaluation of the respective resulting sets of algebraic equations can be represented in terms of state diagrams for gas/solid flows with partial phase separation.
UnivIS-Import:2015-04-16:Pub.1990.tech.ITC.mechve.stated
Keywords: phase; flow; particle

Steady-State-Diagram for Cirulating Fluidized Beds - Wirth, Karl-Ernst (Preprints "International Symposium in Coal Combustion", 1987)
This special issue contains a select 19 of 121 papers presented at the 8th International Symposium on Coal Combustion (ISCC-8), which was held at the Beijing Convention Center on 19−22 July 2015. The first ISCC was inaugurated at Tsinghua University, Beijing, China in 1987 under the consistent support of many distinguished scholars including Prof. Junkai Feng, Prof. Xuchang Xu, Prof. Douglas Smoot, Prof. Adel Sarofim, Prof. Klaus Hein, Prof. Ulrich Renz, Prof. Lothar Reh, Prof. Masayosh Sadakata, Prof. Keiji Makino, and Prof. Jianxiong Mao, etc. Since then, the ISCC has been proudly hosted by Tsinghua University for almost three decades, once every four years, as a non-profit platform to promote Research and Development in the field of science and technology of coal combustion, gasification, and the controls of pollutants and CO2 emissions. The most recent ISCC-8 attracted over 200 engineers and scientists from 14 countries including China, USA, Germany, Japan, UK, Canada, Russia, Australia, Korea, India, Sweden, Poland, Portugal, and Estonia. It was chaired by Prof. Guangxi Yue of Tsinghua University, along with the renewed international advisory committee consisting of 52 leading combustion scholars and experts from 14 countries. For the first time, the ISCC adopted the colloquium chair system to guarantee the quality of the conference papers. After two rounds of peer reviews, 196 technical papers including 5 keynotes, 121 oral presentations and 70 posters were selected, covering six main colloquium topics: <dl class="listitem" id="list_l0005"> – Basic Coal Quality & Combustion – Pulverized Coal Combustion – Fluidized Bed Combustion – Special for CO2 Issues-CCS – Emission Characteristics and Controls – Industrial Application & Coal Utilization. </dl> Among them, 19 papers were chosen for this special issue on FUEL, and other 99 technical papers of high quality were recommended and collected into the Proceedings of the 8th ISCC, to be published by Springer-Tsinghua University Press. The Symposium has once again obtained the vigorous support from the industry as well. International experts from the American Institute of Electrical Engineers, the All-Russian Thermal Engineering Institute and Japanese Coal Company were all present. Domestic experts from the top three power equipment manufacturers, i.e., Harbin Boiler Company Limited, DongFang Boiler Group Co., Ltd. and Shanghai Electric Group, also attended, as well as experts from domestic energy companies like Shenhua, Guodian, and Huaneng groups, thus well representing the global industrial application of clean coal technology. The symposium has strongly reinforced the collaboration and discussion between academic researchers and industry experts, which emphasizes the main theme of the ISCC of establishing an effective bridge between academia and industry. We, all Guest Editors, would like to owe our sincere thanks to FUEL principal editor Prof. John Patrick, and the editorial board of FUEL for giving us the opportunity to publish this special issue of the ISCC-8. We also acknowledge the local organizing committee of the ISCC-8 for organizing a successful symposium, providing passionate services and for recommending these excellent papers. Finally, we thank all the authors and the referees for their contributions in making this issue fruitful and successful.
UnivIS-Import:2015-04-16:Pub.1987.tech.ITC.mechve.steady_73
Keywords: combustion; coal; fluidized; bed

Steady State Diagrams for Circulating Fluidzed Beds - Wirth, Karl-Ernst (Preprints 3rd International Conference on Circulating Fluidized Beds, 1990)
Circulating fluidization is a growing new  technology in  many fields where good  fiuid-solid contact is required. Combustion. power generation, catalytic reactions, drying. waste  incineration and iron ore prereduction ate good examples of its application. New  material processing and other fine technology  area will be  as well included soon. The Third International Conference on Circulating Fluidized Beds (ICCFB- 3) was held at  Nagoya.  Japan. from October 15 to 18. 1990. organized by the Society of Chemical Engineers. Japan in  cooperation with the secretariat of ICCPB. In  this conference the attendants vould have the good balances between academic and  industrial subjects as well as between fundamentals and applications or developments. There were 113  papers from  twenty countries and approximately  133  participants from foreign counlries and 150 from  Japan. To establish common Understandings on the state of  arts in  the  CFB society and at  the same time to  encourage as many people to present their papers or opinions, plenary  lectures. combined oral 8 poster sessions, and workshops were assembled. The conference  language was English. All papers to  be presented at the conference  were handed to  all attendants in  a  form of bounded  loose leaves (preprints). The conference site Nagoya is a cozy city located at  the center of pacific  metropolitan belt of the Mainisland  of Japan. People in  the greater Nagoya  area have been proud of her production of  three SAMURAI heroes in  the age of  feudalistic civil war who after all unified  Japan and opened The Tokugara Era that  lasted for 268 years. Nagoya is surrounded by many  basic  and high-tech  industries  including  automobiles. aircrafts,  electronics, iron and steel,  petroleum  and  petrochemicals. ceramics. etc. Resort and picturesque areas including  Japan Alps mountains.  Kyoto.  Nara  and Ise-Shima are all very close from  Nagoya. within one and half hours travel (by train) or at most  three hours by  car via highways. Business trips to Tokyo and/or Osaka are again very simple if they vere made from Nagoya (two hours to Tokyo and one hour and half to Osaka by  Super Express Hikari)
UnivIS-Import:2015-04-16:Pub.1990.tech.ITC.mechve.steady
Keywords: circulating; fluidized; bed

Steering self-organisation through confinement - Araújo, Nuno A.M.; Janssen, Liesbeth M.C.; Barois, Thomas; Boffetta, Guido; Cohen, Itai; Corbetta, Alessandro; Dauchot, Olivier; Dijkstra, Marjolein; Durham, William M.; Dussutour, Audrey; Garnier, Simon; Gelderblom, Hanneke; et al. (Soft Matter, 2023)
Self-organisation is the spontaneous emergence of spatio-temporal structures and patterns from the interaction of smaller individual units. Examples are found across many scales in very different systems and scientific disciplines, from physics, materials science and robotics to biology, geophysics and astronomy. Recent research has highlighted how self-organisation can be both mediated and controlled by confinement. Confinement is an action over a system that limits its units’ translational and rotational degrees of freedom, thus also influencing the system's phase space probability density; it can function as either a catalyst or inhibitor of self-organisation. Confinement can then become a means to actively steer the emergence or suppression of collective phenomena in space and time. Here, to provide a common framework and perspective for future research, we examine the role of confinement in the self-organisation of soft-matter systems and identify overarching scientific challenges that need to be addressed to harness its full scientific and technological potential in soft matter and related fields. By drawing analogies with other disciplines, this framework will accelerate a common deeper understanding of self-organisation and trigger the development of innovative strategies to steer it using confinement, with impact on, e.g., the design of smarter materials, tissue engineering for biomedicine and in guiding active matter.
CRIS-Team Scopus Importer:2023-03-03

“Sticky” carbon coating enables high-area-capacity lithium storage of silicon-graphitic carbon hybrid - Chen, Zidong; Li, Lun; Zhang, Zheng; Li, Hao; Xie, Bo; Chen, Yungui; Davoodi, Ali; Hosseinpour, Saman; Liu, Wei (Carbon, 2021)
Pulverization and surface instability has been identified as the main impediments to the application of Si anodes in high-energy lithium-ion batteries (LIBs). In this study, a Si-graphitic carbon hybrid (SiG) is created via embedding Si nanoparticles in between expanding graphite interlayers, thus to be adopted as a model system to unravel structure-properties relations for LIBs applications. We explore the impact of artificial surface coating layers on the lithium cycling performance of SiG particles. In comparison with native SiG and carbon-coated SiG (CC-SiG), we find that the “sticky-carbon” coating, i.e., an epoxy-rich layer on top of the carbon coating, gave rise to superior cycle performance. In the “sticky carbon” coated SiG (SCC-SiG), the surface chemistry appears to have a pivotal role in both alleviating electrode disintegration and forming a favorable SEI rich in fluorine-polymers. These positive findings are examined in electrodes with mass loading ranging from 1.0 to 5.0 mg/cm2, achieving area capacities up to 5.0 mAh/cm2. A full cell adopting >6 mg/cm2 LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode and SCC-SiG delivers stable cycling performances. It is hence unraveled that the carbon coating layer with reactive surface groups on the top is an unrecognized key for various Si anodes.<br
Keywords: Si anode; surface moieties; solid electrolyte interface; high-area capacity; lithium storage

Stimuli-Responsive Behavior of PNiPAm Microgels under Interfacial Confinement - Harrer, Johannes; Rey, Marcel; Ciarella, Simone; Löwen, Hartmut; Janssen, Liesbeth M.C.; Vogel, Nicolas (Langmuir, 2019)
The volume phase transition of microgels is one of the most paradigmatic examples of stimuli-responsiveness, enabling a collapse from a highly swollen microgel state into a densely coiled state by an external stimulus. Although well characterized in bulk, it remains unclear how the phase transition is affected by the presence of a confining interface. Here, we demonstrate that the temperature-induced volume phase transition of poly(N-isopropylacrylamide) microgels, conventionally considered an intrinsic molecular property of the polymer, is in fact largely suppressed when the microgel is adsorbed to an air/liquid interface. We further observe a hysteresis in the core morphology and interfacial pressure between heating and cooling cycles. Our results, supported by molecular dynamics simulations, reveal that the dangling polymer chains of microgel particles, spread at the interface under the influence of surface tension, do not undergo any volume phase transition. The balance in free energy responsible for the volume phase transition is fundamentally altered by interfacial confinement. These results imply that important technological properties of such systems, including the temperature-induced destabilization of emulsions, do not occur via a decrease in the interfacial coverage of the microgels.
CRIS-Team Scopus Importer:2019-08-23

Stochastic model to simulate spray fluidized bed agglomeration: a morphological approach - Singh, Abhinandan Kumar; Tsotsas, Evangelos (Powder Technology, 2019)
Keywords: Fractal dimension; Monte Carlo method; Agglomeration; Fluidization; Morphological descriptors; Agglomerate porosity

Stochastic simulation of spray agglomeration process in a continuously operated horizontal fluidized bed by Monte Carlo method - Du, Jiajie; Chen, Kaicheng; Bück, Andreas; Tsotsas, Evangelos (13th International Conference on Fluidized Bed Technology, CFB 2021, 2021)

Stochastic simulation of spray fluidized bed agglomeration by modeling the morphology - Singh, Abhinandan Kumar; Tsotsas, Evangelos (13th International Conference on Fluidized Bed Technology, CFB 2021, 2021)

Stopfgrenze und Druckverlust bei der horizontalen pneumatischen Strähnenförderung in nichtkreisförmigen Rohrquerschnitten - Wirth, Karl-Ernst; Molerus, Otto (Chemie Ingenieur Technik, 1985)
Bei der Einphasenströmung ist die Verwendung kreisförmiger Förderrohre optimal. Die Ursache hierfür ist, dass bei diesen Rohrquerschnitten wegen der Rotationssymmetrie des Strömungsfeldes das Verhältnis von benetzem Umfang zu Rohrquerschnittsfläche und dmit der Druckverlust minimal ist. Die gleichen Überlegungen gelten auch für zweiphasige Gas/Feststoff-Rohrströmungen, solange der Feststoff homogen über den Rohrquerschnitt verteillt ist. Sobald allerdings eine Entmischung der Zweiphasenstromung vorliegt, d. h.,  daB ein Teil des durchgesetzten Feststoffmassenstromes als  Strahne am  Rohrboden  gleitet  und  der  restliche  Anteil  des Feststoffmassenstromes in Form der Flugforderung iiber die Strahne transportiert wird, ist nicht mehr das Verhaltnis von Rohrumfang zu Rohrquerschnittsflache fur den sich einstellenden Druckverlust von  Bedeutung.  In  diesem Fall muB vielmehr die Geometrie der Strahne Auswirkungen auf das Druckverlustverhalten und die minimale  Fordergeschwindigkeit  haben.  Im besonderen  stellt sich die Frage, ob durch  Verwendung eines nichtkreisformigen Rohrquerschnittes die Strahnengeometrie so beeinflufit werden kann, dab im Vergleich zum  Kreisrohr  eine  Reduzierung  der fur eine  sichere Forderung  notwendigen  minimalen  Gasleerrohrgeschwindigkeit (Stopfgrenze) erzielt wird. Ausgehend von der Berechnung des Zusatzdruckverlustes  bei horizontaler pneumatischer Strähnenförderung grobkörniger Feststoffe in einem Förderrohr mit Vollkreisquerschnitt wurden für unterschiedliche Rohrquerschnittsformen der Zusatzdruckverlust und die Stopfgrenze berechnet.
UnivIS-Import:2015-03-05:Pub.1985.tech.ITC.mechve.stopfg
Keywords: druckverlust; förderung; pulver; gas; Feststoff

Stretchable Thermoplastic Elastomer Optical Fibers for Sensing of Extreme Deformations - Leber, Andreas; Cholst, Beth; Sandt, Joseph; Vogel, Nicolas; Kolle, Mathias (Advanced Functional Materials, 2019)
The design of advanced materials with coupled optical and mechanical properties is an important challenge in materials science; especially, the implementation of soft materials in optics has recently gained significant interest. Soft optical systems are particularly versatile in sensing, where large and repeated deformations require dynamically responsive materials. Here, stretchable step-index optical fibers, which are capable of reversibly sustaining strains of up to 300% while guiding light, are demonstrated. A continuous and scalable melt-flow process is used to coextrude two thermoplastic elastomers, thereby forming the fibers' high index core-low index cladding structure. Deformation of the fibers through stretching, bending, and indentation induces detectable, predictable, reversible, and wavelength-dependent changes in light transmission. Quantitative knowledge about the coupling of the fibers' mechanical and optical properties forms the basis for the design of fiber-based sensors that are capable of reliably assessing extreme mechanical stimuli. The fibers utility in sensing scenarios is demonstrated in a knee brace for continuous knee motion tracking, a glove for control of a virtual hand model, and a tennis racket capable of locating ball impacts. Such devices can greatly improve quantitative assessment of human motion in rehabilitation, sports, and anywhere else where large deformations need to be monitored reliably.
CRIS-Team WoS Importer:2019-02-21

Strömungsmechanische Auslegung zirkulierender Wirbelschichtfeuerungen - Wirth, Karl-Ernst (VDI-Berichte, 1989)
UnivIS-Import:2015-03-05:Pub.1989.tech.ITC.mechve.strmun_37

Strömungszustände und Druckverlust in Wirbelschichten - Wirth, Karl-Ernst (VDI-Wärmeatlas, 1991)
UnivIS-Import:2015-04-20:Pub.1991.tech.ITC.mechve.strmun_85

Strömungszustand und Wärmeübergang in zirkulierenden Druckwirbelschichten - Gruber, Uwe; Wirth, Karl-Ernst (Chemie Ingenieur Technik, 1996)
UnivIS-Import:2015-03-05:Pub.1996.tech.ITC.mechve.strmun_6

Strömungszustand und Wärmeübergang in zirkulierenden Wirbelschichten - Wirth, Karl-Ernst (VDI-Berichte, 1993)
Zirkulierende Druckwirbelschichtfeuerungen ermoglichen gegenuber atmospharisch betriebenen Anlagen eine deutliche Steigerung der thermischen Querschnittsbelastung und damit eine kompaktere  Bauweise. Zur Auslegung soicher Anlagen werden insbesondere Kenntnisse uber den in der Brennkammer  vorliegenden  Stromungszustand  und  den wandseitigen Wanneubergang benotigt. Der Stromungszustand im Aufstromteil von zirku- lierenden Wirbelschichten hangt im wesentlichen von der Partikel-Froude-Zahl,  einer  dimensionslosen  Form  der Leerrohrgasgeschwindigkeit ab. In atmospharisch  be- triebenen Anlagen sind die Leerrohrgasgeschwindigkeiten i.a. aus  VerschleiRgriinden  auf 5 bis 6m/s begrenzt, so dal3 nur kleine Partikel-Froude-Zahlen von 1 bis 2 erreicht werden. Der Stromungszustand bei diesen Partikel-Froude-Zahlen  ist  dadurch  gekennzeichnet,  daR  zwei  Hohenabschnitte mit jeweils konstantem Druckgradienten, auch Behamngsstrecken genannt, vorliegen. Unmittelbar uber dem Anstromboden befindet sich eine Zone hoher Feststoffkonzentration und im oberen Aufstromteil eine Zone mit geringerer Feststoffkonzentration. Unter Druck sind jedoch  aufgrund der hoheren Gasdichte wesentlich  geringere  Leerrohrgasgeschwindigkeiten zur Erzielung der in atmospharisch betriebenen Wirbelschichtfeuerungen  ublichen  kleinen  Partikel-Froude-Zahlen notwendig. Das Potential von zirkulierenden Druckwirbelschichten wird erst dann vollstandig genutzt, wenn unter  Druck ahnlich hohe Leerrohrgasgeschwindigkeiten wie in atmospharisch betriebenen Anlagen eingestellt werden. Aufgrund der dann groRen Partikel-Froude-Zahlen ist zu envarten, daR  sich der Stromungszustand andert. Da die Warmeabfuhr  in  zirkulierenden  Druckwirbelschichtfeue- rungen  i. a.  uber  die  Brennkammenvande  erfolgt,  hatte dies auch Konsequenzen für die warmetechnische  Auslegung
UnivIS-Import:2015-03-05:Pub.1993.tech.ITC.mechve.strmun_31

Structural and mechanical evaluation of a nanocrystalline A1–5 wt %si alloy produced by mechanical alloying - Dayani, Davood; Shokuhfar, Ali; Vaezi, Mohammad Reza; Rezaei, Seyed Reza Jafarpour; Hosseinpour, Saman (Metals, 2017)
Keywords: Mechanical properties; Si alloy; Al; Mechanical alloying; Consolidation

Structural Color of Colloidal Clusters as a Tool to Investigate Structure and Dynamics - Wang, Junwei; Sultan, Umair; Görlitzer, Eric; Mbah Chrameh, Fru; Engel, Michael; Vogel, Nicolas (Advanced Functional Materials, 2019)
Colloidal assemblies have applications as photonic crystals and templates for functional porous materials. While there has been significant progress in controlling colloidal assemblies into defined structures, their 3D order remains difficult to characterize. Simple, low-cost techniques are sought that characterize colloidal structures and assist optimization of process parameters. Here, structural color is presented to image the structure and dynamics of colloidal clusters prepared by a confined self-assembly process in emulsion droplets. It is shown that characteristic anisotropic structural color motifs such as circles, stripes, triangles, or bowties arise from the defined interior grain geometry of such colloidal clusters. The optical detection of these motifs reliably distinguishes icosahedral, decahedral, and face-centered cubic colloidal clusters and thus enables a simple yet precise characterization of their internal structure. In addition, the rotational motion and dynamics of such micrometer-scale clusters suspended in a liquid can be followed in real time via their anisotropic coloration. Finally, monitoring the evolution of structural color provides real-time information about the crystallization pathway within the confining emulsion droplet. Together, this work demonstrates that structural color is a simple and versatile tool to characterize the structure and dynamic properties of colloidal clusters.
CRIS-Team Scopus Importer:2019-11-26
Keywords: colloidal clusters; confinement; crystallization; self-assembly; structural color; supraparticles

Structural dependent drag force and orientation prediction for small fractal aggregates - Binder, Christian; Hartig, Martin Andreas Johannes; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2009)
Aggregates settle in viscous fluids in specific directions depending on their morphology. We investigated the settling behavior of fractal aggregates with D = 1.85 in fluids using the Accelerated Stokesian Dynamics method. The results have been compared with experimental data. A simple equation is proposed which gives the drag force in dependence on the radius of gyration r, the projection area A and the aggregate orientation during settling. This equation reproduces the data from ASD within ± 10 % for Re <1. Additionally, a new algorithm has been developed which allows a prediction of the orientation of such fractal aggregates provided that they have time enough to orient in the fluid. Moreover, the drag force acting on them can be predicted in a narrow range (maximum error 15%). This algorithm allows a very fast evaluation of the orienting behavior with small deviations. © 2008 Elsevier Inc. All rights reserved.
Keywords: Aggregate behavior; Drag force; Fractal aggregates; Hydrodynamics; Stokesian Dynamics

Structural factors controlling size reduction of graphene oxide in liquid processing - Nacken, Thomas; Halbig, Christian E.; Wawra, Simon; Damm, Cornelia; Romeis, Stefan; Walter, Johannes; Tehrani, Mohammad J.; Hu, Yichen; Ishii, Yoshitaka; Eigler, Siegfried; Peukert, Wolfgang (Carbon, 2017)
Graphene oxide materials can be prepared in manifold synthesis approaches and allow for further post-functionalization to adopt the properties of the desired application. Small sized sheets with lateral dimensions on the 100 nm scale are e.g. beneficial for cell applications. Breakage of sheets by liquid phase processing is an ideal way to generate such nano-sized sheets. However, until now it is unknown how functionalization influences the breakage behavior. We have chosen single layered oxo-functionalized graphene (oxo-G) derivatives with lattice defects < 1% to evaluate their size reduction rate upon ultrasonication of flakes with respect to the type and degree of functionalization of the graphene sheets. Lateral dimensions of the processed sheets were quantitatively determined in solution by analytical ultracentrifugation. The highest size reduction rate is observed for pristine oxo-G, which bears the highest degree of functionalization of around 60% and the negatively charged organosulfate group. Partial hydrolysis of organosulfate, or conversion of surface-functional groups to hydroxyl-groups in majority or partial defunctionalization lead to size-reduction rates which are up to 25% lower in comparison with the initial oxo-G. Moreover, the size reduction rate can be correlated in first approximation also with UV–vis spectroscopy.

Structural influence on the drag of fractal aggregates - Peukert, Wolfgang; Binder, Christian (The 2007 Annual Meeting Salt Lake City, UT, 2007)
Aggregates typically formed in aerosol processes have a fractal dimension of Df=1.85. These aggregates suspended in a fluid flow have a behavior dependent on their structure, very different from the behaivor of a volume equivalent sphere in a fluid. The drag is considerably changing with increasing particle number and the settling behavior changes too, especially when the aggregates have enough time to relax into a quasi-equilibrium state and follow the streamlines. Simulation of the settling of such aggregates consisting of equally sized spheres generated by a Monte Carlo method using diffusion limited cluster-cluster aggregation has been performed on the basis of the Stokesian Dynamics method developed by Bossis and Brady, yielding approximations of the drag force in dependency on the aggregate number and the projected area. The dependency of the settling velocity and the drag on the structure of random aggregates will be shown by correlations with parameters characterizing the morphology of each aggregate.
Keywords: monte; carlo; stokesian; simulation; drag; settling; particle; aerosol; aggregate

Structure and adsorption behavior of high hydrostatic pressure-treated β-lactoglobulin - Kieserling, Helena; Giefer, Patrick; Uttinger, Maximilian; Lautenbach, Vanessa; Nguyen, Thu; Sevenich, Robert; Lübbert, Christian; Rauh, Cornelia; Peukert, Wolfgang; Fritsching, Udo; Drusch, Stephan; Maria Wagemans, Anja (Journal of Colloid and Interface Science, 2021)
Hypothesis: High hydrostatic pressure treatment causes structural changes in interfacial-active β-lactoglobulin (β-lg). We hypothesized that the pressure-induced structural changes affect the intra- and intermolecular interactions which determine the interfacial activity of β-lg. The conducted experimental and numerical investigations could contribute to the mechanistic understanding of the adsorption behavior of proteins in food-related emulsions. Experiments: We treated β-lg in water at pH 7 with high hydrostatic pressures up to 600 MPa for 10 min at 20 °C. The secondary structure was characterized with Fourier-transform infrared spectroscopy (FTIR) and circular dichroism (CD), the surface hydrophobicity and charge with fluorescence-spectroscopy and ζ-potential, and the quaternary structure with membrane-osmometry, analytical ultracentrifugation (AUC) and mass spectrometry (MS). Experimental analyses were supported through molecular dynamic (MD) simulations. The adsorption behavior was investigated with pendant drop analysis. Findings: MD simulation revealed a pressure-induced molten globule state of β-lg, confirmed by an unfolding of β-sheets with FTIR, a stabilization of α-helices with CD and loss in tertiary structure induced by an increase in surface hydrophobicity. Membrane-osmometry, AUC and MS indicated the formation of non-covalently linked dimers that migrated slower through the water phase, adsorbed more quickly due to hydrophobic interactions with the oil, and lowered the interfacial tension more strongly than reference β-lg.
CRIS-Team Scopus Importer:2021-04-16
Keywords: Adsorption rate; High pressure processing; Lag time; Molecular dynamic simulation; Oil/water-interface; Pendant drop; Protein structure analysis

Structure and dynamics of interfacial peptides and proteins from vibrational sum-frequency generation spectroscopy - Hosseinpour, Saman; Roeters, Steven; Bonn, Mihscha; Peukert, Wolfgang; Woutersen, Sander; Weidner, Tobias (Chemical Reviews, 2020)
Proteins at interfaces play an important role in cell biology, immunology, bioengineering, and biomimetic material design. Many biological processes are based on interfacial protein action, ranging from cellular communication to immune responses and the protein-driven mineralization of bone. Despite the importance of interfacial proteins, comparatively little is known about their structure. The standard methods for studying crystalline or solution-phase proteins (X-ray diffraction and NMR) are not well suited for studying proteins at interfaces, and for these proteins, we still lack a corresponding technique that can provide the same level of structural resolutions. This is not surprising in view of the challenges involved in probing the structure of proteins within monomolecular films assembled at a very thin interface in situ. Vibrational sum-frequency generation (SFG) spectroscopy has the potential to overcome this ‘resolution gap’ and investigate the structure and dynamics of proteins at interfaces at the molecular level and with sub-picosecond time resolution. While SFG studies were initially limited to simple model peptides, the past decade has seen a dramatic advancement of experimental techniques and data analysis methods, which has made it possible to also study interfacial proteins and their folding, binding, orientation, hydration, and dynamics. In this review, we first explain the principles of protein SFG and the experimental and theoretical methods to measure and analyze protein SFG spectra. Then we give an extensive overview of the interfacial proteins studied thus far with SFG. We highlight representative examples to demonstrate recent advances in probing the structure of proteins at the interfaces of liquids, membranes, minerals, and synthetic materials.<br
Keywords: Biomimetic materials; Biomimetics; Bone; Cytology; Dynamics; Interferometry; Membranes; Nuclear magnetic resonance spectroscopy; PeptidesSurface chemistry; Biological process; Data analysis methods; Experimental techniques; Molecular levels; Structure and dynamics; Synthetic materialsTheoretical methods; Vibrational sum-frequency generations; Interfaces (materials); Liquid-Air Interface; Vibrational Spectrum; Heterodyne

Structuring of surfaces with the aid of polymer stamping structures - Peukert, Wolfgang; Winzer, Bettina (Chemie Ingenieur Technik, 2006)
Oberflächen, die hinsichtlich der Benetzungseigenschaften über Microcontact-Printing vorstrukturiert sind, können in weiteren Experimenten zur geordneten Anlagerung von verschiedensten kolloidalen Partikeln eingesetzt werden. Bei entsprechender Wahl der Stabilitätsbedingungen in der Lösung, der Partikelkonzentration und der Trocknungsbedingungen des Films erhält man geordnete Strukturen von Mikro- und Nanopartikeln auf lokal scharf abgegrenzten Oberflächenbereichen.
Keywords: oberfläche; nanostruktur; benetzung; microcontact; trocknung

Studies of the Solubility of BaSO4 Nanoparticles in Water: Kinetic Size Effect, Solubility Product, and Influence of Microporosity - Vogelsberger, Wolfram; Schmidt, Jochen (Journal of Physical Chemistry C, 2011)
Dissolution experiments are carried out with nanoparticles of barium sulfate in water. An unusual concentration-time behavior is observed. A concentration maximum is measured at the very beginning of the dissolution process. This maximum considerably exceeds the saturation concentration of bulk material. The maximum concentration is followed in time by a decrease of the g concentration until the saturation concentration of the bulk material is obtained. This behavior is called kinetic size effect and it is a characteristic of nanoscale particles in general. The colloidal system can be modeled theoretically by thermodynamic and kinetic considerations that cover all processes which may occur in the system: nucleation, particle growth, Ostwald ripening, and dissolution of particles. It has been shown that only the outer surface of the particles is responsible for the dissolution kinetics; it is suggested that the surface of micropores yields no contribution. The dissolution curves observed experimentally follow from the model considerations. It is possible by comparison of experiment and theory to estimate the saturation concentration influenced by the ionic strength in the solution. This effect can be well described by the extended Debye-Huckel law. The measured numerical values of the saturation concentrations are found to be in the range of 4-14 mu mol L-1 and therefore in the vicinity of the solubility product of BaSO4. The saturation activity at infinite dilution (I -> 0) is a(Bn)(infinity) = 2.43 +/- 0.12 mu mol L-1 and the thermodynamic solubility product is K-L(infinity) = 10(-11.23). Furthermore, the model calculations provide the possibility to estimate the interfacial tension of the system nanopartide - solution. The numerical value of 1.1 N m(-1) is obtained. The error of the estimated interfacial tension is approximately as large as about 15%. This seems to be acceptable in view of a lack of reliable data in the literature. It is possible furthermore to calculate a kinetic rate constant for any changes that may occur in the colloidal system. The error of this rate constant, however, may be as large as a factor of 10.

Study of amphiphilic polyester micelles by hyper-rayleigh scattering: Invertibility and phase transfer - Peukert, Wolfgang; Martinez Tomalino, Lars-Owe; Voronov, Andriy; Kohut, Ananiy (Journal of Physical Chemistry B, 2008)
For the first time, hyper-Rayleigh scattering (HRS) of invertible polymeric micellar structures has been measured. HRS measurements on amphophilic invertible polyesters with alternating hydrophilic and hydrophobic fragments were carried out in solvents of differing polarity. The observed strong variation of the HRS signals is attributed to the switching behavior of the polyester micelles in the different solvents. The hyperpolarizabilities and the size of the micelles increased with decreasing polarity of the solvent. Observing the dynamics of the solubilization of an insoluble dye (malachite green) by the invertible polyester in toluene confirmed the possibility to reveal conformational changes in polyester macromolecules by HRS. In contrast to UV measurements which showed a continuous increase in absorbance and indicated overall solubilization of the dye, the HRS signals decreased after approaching a maximum value. The decrease of the HRS signals is attributed to the change of dye molecules' orientation within the micelles due to the change of polymeric conformation in toluene. The results have shown that HRS is sensitive to reorientation and ordering of the macromolecules and might become a powerful tool for studying polymer micellar structures as well as phase transfer processes at the nanoscale. © 2008 American Chemical Society.
Keywords: rayleigh; scattering; polymer; structure; polarizability; hydrophilic; hydrophobic

Study of particle synthesis in a low pressure plasma reactor using time resolved laser induced annealing technique (TIRE-LII) - Peukert, Wolfgang; Leipertz, Alfred; Sommer, Roland; Artelt, Christian (Chemie Ingenieur Technik, 2005)
Bei der Partikelsynthese in gepulsten, d. h. äußerst kurzzeitigen Plasmen stellt die Steuerung von Produkteigenschaften mit Hilfe von Prozessparametern einen sehr wichtigen Aspekt dar. Um deren Einfluss bei der Rußsynthese unter Niederdruck auf die Bildungs und Wachstumskinetik besser verstehen und kontrollieren zu können, ist es notwendig, charakteristische Teilcheneigenschaften wie die Primärpartikelgröûe online und in situ zu bestimmen. Eine hierfür geeignete Messmethode stellt prinzipiell die zeitaufgelöste laserinduzierte Glühtechnik (TIRE-LII) dar, deren Anwendbarkeit zur Ruûcharakterisierung an groûtechnischen Produktionsreaktoren unter Atmosphärendruck bereits in den vergangenen Jahren erfolgreich aufgezeigt werden konnte [1]. Bei der laserinduzierten Glühtechnik werden die Teilchen durch einen hochenergetischen Laserpuls bis auf annähernd Sublimationstemperatur aufgeheizt, anschlieûend werden deren spektral und zeitlich aufgelöste Temperatur- bzw. Signalverläufe analysiert. Unter Atmosphärendruck stellt dabei die Wärmeleitung an das umgebende Gas den dominierenden Energieabgabemechanismus zu späteren Zeitpunkten nach dem Laserpuls dar. Deshalb kühlen die Teilchen aufgrund ihrer spezifischen Oberfläche unterschiedlich schnell ab, was sich direkt im Signalverlauf widerspiegelt. Um die Messtechnik zur Bestimmung der Partikelgröûe auch unter Niederdruck einzusetzen, ist eine Modifizierung und experimentelle Validierung des zugrunde liegenden LII-Modells für freie Molekülbewegung notwendig. Bei der experimentellen Realisierung wurde als Anregungsquelle ein gepulster Nd:YAG-Laser eingesetzt und die dadurch induzierte  Inkandeszenz mittels entsprechender Detektionsoptik und schnellem Photomultiplier punktuell erfasst. Zur Analyse der Partikelbildung wurden Untersuchungen für verschiedene Plasmaleistungen, Precursorkonzentrationen und Umgebungsdrücke durchgeführt. Auûerdem konnte der Einfluss von unterschiedlichen Inertgasen bei Unterdruck betrachtet werden.
Keywords: Laser; Glühtechnik; Pplasma; Partikel; Niederdruck

Substituting fossil-based with bio-based chemicals: the case of limonene as a greener pore expander for micellar templated silica - Sultan, Umair; Städtke, Katrin; Göpfert, Andreas; Lemmen, Daniel; Metwali, Ezzeldin; Maiti, Santanu; Schlumberger, Carola; Yokosawa, Tadahiro; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Vogel, Nicolas; Unruh, Tobias; et al. (RSC Sustainability, 2023)
Porous materials are widely used in applications such as adsorption, catalysis and separation. The use of expander molecules is a versatile route to enlarge the mesopore size in micellar templated mesoporous silica materials. Typical expanders used for this purpose are fossil-based organic molecules such as trimethylbenzene (TMB). In the course of making such syntheses greener and more sustainable, it is highly desirable to substitute such fossil-based chemicals with renewable ones. Here, we show that bio-based limonene can be used as an alternative expander molecule for the synthesis of large-pore templated silica. On the basis of electron microscopy, nitrogen physisorption and small angle X-ray scattering we show that the substitution of TMB by limonene leads to very similar material characteristics, reaching mean mesopore diameters of 17-19 nm. A comparative life-cycle assessment demonstrates the reduced environmental impact of limonene production from citrus peel waste compared to TMB production, supporting the call for more applications of renewable chemicals, ideally from waste-streams, also for the production of porous materials.
CRIS-Team Scopus Importer:2023-10-06

Substrate-Independent Design of Liquid-Infused Slippery Surfaces via Mussel-Inspired Chemistry - Chiera, Salvatore; Bittner, Carina; Vogel, Nicolas (Advanced Materials Interfaces, 2021)
Self-cleaning and repellent coatings ensure enduring performance of surfaces in many areas of technology and everyday life. An ideal repellent coating is efficient in removing contaminations, yet easy to apply on a wide range of surface materials. To devise such a coating, two bioinspirations are combined that show opposing interfacial properties: the peristome of a pitcher plant and the versatile mussel-inspired chemistry of polydopamine (PDA). The possibility of PDA to bind to different surface materials is taken to provide a material-independent coating strategy. Its reactivity toward amines to cofunctionalize the coating with monoaminopropyl-polydimethylsiloxane is utilized to control the surface chemistry. This process, in effect, adheres silicone polymer chains to any desired surface material. Finally, inert silicone oil is added to the reaction mixture to provide in situ lubrication of the coating. Together, the process creates lubricant-infused surfaces in a one-step process independent of the underlying substrate. It is shown that the reaction mixture can be deposited by dip or spray coating, providing procedures to coat large surfaces and complex samples such as textiles and wood. The combination of the mussel-inspired chemistry with the pitcher plant-inspired control of wettability provides an experimentally simple coating process to impart efficient repellency and self-cleaning characteristics to virtually any surface material.
CRIS-Team Scopus Importer:2021-05-14
Keywords: liquid infused surfaces; liquid repellency; mussel-inspired chemistry; polydopamine; slippery surfaces; spray coating

Superheated atomization - Günther, Astrid; Wirth, Karl-Ernst (Process-Spray: Functional Particles Produced in Spray Processes, 2016)
The project “Superheated atomization", located at the Institute of Particle Technology (University of Erlangen-Nuremberg), focused on the characterization and evaluation of flash-or superheated-atomization. Flash atomization is based on a phase transition within or outside a nozzle, induced by a superheating prior to spraying. A multiphase flow can exists in the atomizer, containing bubbles with a higher inner pressure (corresponding to the vapor pressure of the sprayed fluid pv) than the ambient pressure p∞. These bubbles burst at the nozzle outlet, thereby disintegrating the fluid and generating a dispersed spray. Dependent on process conditions (e.g., fluid temperature T0), nozzle geometry (e.g., L/D-ratio) and fluid material properties (e.g. shear viscosity η) different spray morphologies occur. Furthermore spray properties like the characteristic mean droplet size (Sauter mean diameter x32) or spray temperature (Tm) are influenced by the flow conditions inside the nozzle. In order to characterize the resulting spray, the flow behavior inside the nozzle has to be analyzed. Therefore, measurements like mass flux determination are conducted. For the general characterization of the superheated atomization, plain water is used. Furthermore, more complex media like polyvinylpyrrolidone solutions are sprayed and differences are monitored. The results are combined with measurement data of the spray itself, like droplet velocities, determined with Particle Image Velocimetry (PIV), allowing a dimensionless description of the whole atomization process. The superheated atomization enables the generation of a finely dispersed spray with a variety of atomizer geometries. Due to the fact that the shear viscosity is lowered with increasing fluid temperature, comparably fine droplets size distributions are formed, even for rather high subcooled shear viscosity values. In respect to particle formation, it its advantageous that 2-10% of the fluid is evaporated as a side effect of the spraying process. Therefore, less liquid has to be removed in a downstream drying step for particle formatio

Superheated Atomization: Influence of Nozzle Geometry on Mass Flux and Spray Characteristics - Wirth, Karl-Ernst; Günther, Astrid (Chemie Ingenieur Technik, 2012)
The atomization of superheated liquids utilizes thermal energy for partial evaporation of flow media, by this enhancing the spray disintegration. The degree of evaporation and the generation of big droplets is a function of the nozzle geometry. By analyzing mass fluxes and by application of optical measurement techniques geometry- dependent modifications of flow characteristics and spray morphology are investigated.
Keywords: Flow rate; Nozzle geometry; Optical measurement techniques; Spray

Supported liquid metals - A new class of robust dehydrogenation catalysts - Taccardi, Nicola; Grabau, Mathias; Debuschewltz, Jonas; Distaso, Monica; Brandl, Marco; Hock, Rainer; Maier, Florian; Papp, Christian; Erhard, Jannis; Neiß, Christian; Peukert, Wolfgang; Görling, Andreas; et al. (12th Natural Gas Conversion Symposium 2019, 2019)
CRIS-Team Scopus Importer:2019-12-10

Suppressing non-controlled leakage of hydrophilic payloads from redox-responsive nanocapsules - Hosseinpour, Saman; Behzadi, Shahed; Stadler, Jochen; Crespy, Daniel; Landfester, Katharina (Colloids and Surfaces A-Physicochemical and Engineering Aspects, 2017)
Nanocapsules with a hydrophilic core are particularly interesting for biomedical and anticorrosion applications since these nanocontainers allow encapsulating a wide range of hydrophilic payloads and controlling their release profiles. However, a major challenge associated with the preparation of these nanocapsules is the non-controlled leakage of hydrophilic payloads from the core due to osmotic pressure. Herein, we present an approach for the preparation of polymer nanocapsules that suppress the non-controlled leakage of payloads and respond to chemical reduction that triggers release of encapsulated payloads. The non-controlled leakage of hydrophilic payloads from the nanocapsules is hindered by increasing the shell thickness. These nanocapsules consisting of reduction-responsive units possess a remarkable release property only under reductive condition while cease non-controlled leakage of the payload in the aqueous release medium. The described nanocapsules can be applied for biomedical and anticorrosion applications in which triggered release of hydrophilic payloads is suitabl
Keywords: Nanocapsules; Controlled-release; Redox-responsive; Shell thickness

Supraparticles: Functionality from Uniform Structural Motifs - Wintzheimer, Susanne; Granath, Tim; Oppmann, Maximilian; Kister, Thomas; Thai, Thibaut; Kraus, Tobias; Vogel, Nicolas; Mandel, Karl (ACS nano, 2018)
Under the right process conditions, nanoparticles can cluster together to form defined, dispersed structures, which can be termed supraparticles. Controlling the size, shape, and morphology of such entities is a central step in various fields of science and technology, ranging from colloid chemistry and soft matter physics to powder technology and pharmaceutical and food sciences. These diverse scientific communities have been investigating formation processes and structure/property relations of such supraparticles under completely different boundary conditions. On the fundamental side, the field is driven by the desire to gain maximum control of the assembly structures using very defined and tailored colloidal building blocks, whereas more applied disciplines focus on optimizing the functional properties from rather ill-defined starting materials. With this review article, we aim to provide a connecting perspective by outlining fundamental principles that govern the formation and functionality of supraparticles. We discuss the formation of supraparticles as a result of colloidal properties interplaying with external process parameters. We then outline how the structure of the supraparticles gives rise to diverse functional properties. They can be a result of the structure itself (emergent properties), of the colocalization of different, functional building blocks, or of coupling between individual particles in close proximity. Taken together, we aim to establish structure-property and process-structure relationships that provide unifying guidelines for the rational design of functional supraparticles with optimized properties. Finally, we aspire to connect the different disciplines by providing a categorized overview of the existing, diverging nomenclature of seemingly similar supraparticle structures.
CRIS-Team Scopus Importer:2020-04-02
Keywords: agglomeration; building blocks; colloids; complex particles; functionality; hierarchy; nanostructures; self-assembly; supraparticles

Surface activity of new invertible amphiphilic polyesters based on poly(ethylene glycol) and aliphatic dicarboxylic acids - Voronov, Andriy; Vasylyev, Serhiy; Kohut, Ananiy; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2008)
The surface active properties of aqueous solutions of invertible amphiphilic alternated polyesters differing by hydrophilic-lipophilic balance (HLB) and molecular weight have been determined over the wide concentration range. The polyesters are based on poly(ethylene glycol) (PEG) of two molecular weights and aliphatic dicarboxylic acids (decanedioic and dodecanedioic). The surface activity of the polyesters and their ability to form micellar assemblies (which was recently shown for organic solvents) has been confirmed in water. The central role of the balance of hydrophilic to hydrophobic groups ratio in the formation of polymeric arrangements having hydrophobic pockets and external hydrophilic shell has been shown. The effect of molecular weight has been found considerable as well. Two changes in slope have been observed for the more hydrophobic polyesters in the surface tension vs log concentration curve. The change at low concentration is believed to originate from the formation of polyester assemblies with a hydrophobic interior and hydrophilic exterior due to the interaction of hydrophobic fragments and macromolecular flexibility. The higher concentration region exhibits behavior consistent with a cmc, which was confirmed by additional dye solubilization experiments. Molecular structure of the polyester micelles is determined by the solubilization of a solvatochromic dye. The experiment confirmed that micellization of polyesters is accompanied by the association of more hydrophobic (aliphatic) constituents forming the micelle interior. The hydrophilic fragments (ethylene oxide groups) are involved in the formation of micelle exterior. © 2008 Elsevier Inc. All rights reserve
Keywords: Assemblies with a hydrophobic interior and hydrophilic exterior; Hydrophobic effect; Invertible amphiphilic polyesters

Surface Charging and Interfacial Water Structure of Amphoteric Colloidal Particles - Peukert, Wolfgang; Braunschweig, Björn; Sauerbeck, Christian (Journal of Physical Chemistry C, 2014)
Colloidal stability and adsorption processes at particle surfaces are controlled by the generation of surface charge and the molecular structure of the resulting electrical double layers. We have applied second-harmonic light scattering (SHS) to address doublelayer charging and the orientation of water molecules at surfaces of amphoteric particles in unprecedented detail. For that purpose we have performed the first SHS experiments of neat polystyrene particles with a mixture of sulfate (R−O−SO3-) and amino (R-NH2) functional groups. Changing the pH has a dramatic effect on the surface potential which can be tuned from positive to negative values and has allowed us to record changes in SHS signal while the isoelectric point of the particles is being crossed. The SHS signal is a function of two contributions which are directly related to the first molecular layer, its orientation, and to a second electric field induced contribution of the unidirectional field within the interfacial electric double layer. Through additional charge screening experiments we measured the surface charge density for positively as well as for negatively charged particle surfaces and confirmed the isoelectric point, where an increase in ionic strength had little effect on the SHS intensity. Furthermore, we have determined the net orientation of water molecules directly adsorbed to the particle surface from pH-dependent changes in the relative phase of the two SHS contributions.
Keywords: colloid; adsorption; particle; surface; charge; electric; ionic; strength; double; layer

Surface decoration of MgO nanocubes with sulfur oxides: Experiment and theory - Sternig, Andreas; Diwald, Oliver; Gross, Silvia; Sushko, Peter V. (Journal of Physical Chemistry C, 2013)

Surface exciton separation in photoexcited MgO nanocube powders - Sternig, Andreas; Stankic, Slavica; Mueller, Markus; Siedl, Nicolas; Diwald, Oliver (Nanoscale, 2012)
In MgO nanocube powders surface excitons can separate and the resulting charge carriers provide reactive adsorption sites at well-defined surface elements. We employed photoluminescence (PL) emission bands originating from the photoexcitation of nanocube corners and edges as quantitative probes to explore their chemical reactivity towards molecular hydrogen. Surface excitons which form at corners and edges exhibit similar cross-sections for separation in vacuum. The separation of edge excitons, however, is significantly enhanced in hydrogen atmosphere when hydrogen adsorption occurs as a simultaneous surface process. The electronic structure of MgO nanocube edges which split hydrogen heterolytically upon generation of surface hydroxyls and hydrides is unaffected by the photoexcitation of corners. Respective edges, however, are efficient absorption sites for UV photons. Transfer of exciton energy to oxygen ions in corners is followed by exciton separation which transforms corner ions into surface radicals leading to a well-defined starting point for the site selective functionalization of metal oxide nanostructures.
Keywords: nanoparticle

Surface functionalization and electronic interactions of ZnO nanorods with a porphyrin derivative - Klaumünzer, Martin; Kahnt, Axel; Burger, Alexandra; Mackovic, Mirza; Muenzel, Corinna; Srikantharajah, Rubitha; Spiecker, Erdmann; Hirsch, Andreas; Peukert, Wolfgang; Guldi, Dirk Michael (ACS Applied Materials and Interfaces, 2014)
To optimize electron transfer and optoelectronic properties in nanoparticulate thin films for electronics we show the surface functionalization of ZnO nanorods by means of replacing surface active 2-[2-(2-methoxyethoxy) ethoxy]acetic acid (TODA) by a redoxactive organic component, that is, 5,10,15,20-(phenoxyacetat)-porphyrin bearing four carboxylic acids as possible ZnO anchors. Microscopy-transmission electron microscopy-And spectroscopy-optical spectroscopy-verifies the successful and homogenous integration of the porphyrin onto the surface of ZnO nanorods, a process that is facilitated by the four anchoring groups. Photophysical investigations based on emission and absorption spectroscopy prompt to distinct electronic interactions between ZnO nanorods and the porphyrins. Consequently, we performed further photophysical studies flanked by pulse radiolysis assays to corroborate the nature of the electronic interactions. © 2014 American Chemical Society.

Surface functionalization of ZnO nanorods with C60 derivatives carrying phosphonic acid functionalities - Voigt, Michael; Klaumünzer, Martin; Ebel, Alexander; Werner, Fabian; Yang, Guang; Marczak, Renata; Spiecker, Erdmann; Guldi, Dirk Michael; Hirsch, Andreas; Peukert, Wolfgang (Journal of Physical Chemistry C, 2011)
ZnO with its wide band gap (3.37 eV) emerged as a promising semiconductor material for applications in the fields of printable and flexible electronics such as field effect transistors, etc. The fact that contacts at particle/particle interfaces exert a limiting impact on device performances motivates research on aligning the electronic levels at particle/particle interfaces. To this end, we focus in the present study on the surface functionalization of ZnO nanorods by a series of C derivatives. The latter share in common (i) a phosphonic acid as an anchor to ZnO, (ii) an alkyl chain as a flexible spacer, and (iii) a C as the headgroup. To shed light onto the electronic interactions between ZnO and C, we vary the alkyl chain length from n = 3 to n = 18. HRTEM and EELS prove the successful surface functionalization. Fundamental to this work are steady state absorption and photoluminescence measurements, which confirm the presence of appreciable electronic couplings between ZnO nanorods and C. Especially the photoluminescence measurements are important since they provide strong support for the dependence between spacer length and strength of electronic communication. In particular, a blue-shift of the ZnO free exciton emission band amounting to as much as 50 meV is observed with a decrease in spacer length. Furthermore, time-resolved absorption measurements corroborate ultrafast charge injection - facilitated by strong coupling - from the photoexcited ZnO nanorods to C. © 2011 American Chemical Society.
Keywords: Functionalization; Oxides; Reaction products; Organophosphorus compounds; Nanorods

Surface Modification of ZnO Nanorods with Hamilton Receptors - Hirsch, Andreas; Peukert, Wolfgang; Zeininger, Lukas; Klaumünzer, Martin (International Journal of Molecular Sciences, 2015)
A new prototype of a Hamilton receptor suitable for the functionalization of inorganic nanoparticles was synthesized and characterized. The hydrogen bonding receptor was coupled to a catechol moiety, which served as anchor group for the functionalization of metal oxides, in particular zinc oxide. Synthesized zinc oxide nanorods [ZnO] were used for surface functionalization. The wet-chemical functionalization procedure towards monolayer-grafted particles [ZnO-HR] is described and a detailed characterization study is presented. In addition, the detection of specific cyanurate molecules is demonstrated. The hybrid structures [ZnO-HR-CA] were stable towards agglomeration and exhibited enhanced dispersability in apolar solvents. This observation, in combination with several spectroscopic experiments gave evidence of the highly directional supramolecular recognition at the surface of nanoparticles.
Keywords: nanorod; functional; particle; ZnO; zinc; oxide; monolayer; stabilization

Surface Patterning with SiO2@PNiPAm Core–Shell Particles - Tang, Jo Sing; Bader, Romina Sigrid; Görlitzer, Eric; Wendisch, Jan Fedja; Bourret, Gilles Remi; Rey, Marcel; Vogel, Nicolas (ACS Omega, 2018)
Colloidal lithography is a cost-efficient method to produce large-scale nanostructured arrays on surfaces. Typically, colloidal particles are assembled into hexagonal close-packed monolayers at liquid interfaces and deposited onto a solid substrate. Many applications, however, require non close-packed monolayers, which are more difficult to fabricate. Preassembly at the oil/water interface provides non close-packed colloidal assemblies but these are difficult to transfer to a solid substrate without compromising the ordering due to capillary forces acting upon drying. Alternatively, plasma etching can reduce a close-packed monolayer into a non close-packed arrangement, however, with limited interparticle distance and compromised particle shape. Here, we present a simple alternative approach toward non close-packed colloidal monolayers with tailored interparticle distance, high order, and retained spherical particle shape. We preassemble poly(N-isopropylacrylamide)-silica (SiO2@PNiPAm) core–shell particles at the air/water interface, transfer the interfacial spacer to a solid substrate, and use the polymer shell as a sacrificial layer that can be thermally removed to leave a non close-packed silica monolayer. The shell thickness, cross-linking density, and the phase behavior upon compression of these complex particles at the air/water interface provide parameters to precisely control the lattice spacing in these surface nanostructures. We achieve hexagonal non close-packed arrays of silica spheres with interparticle distances between 400 and 1280 nm, up to 8 times their diameter. The retained spherical shape is advantageous for surface nanostructuring, which we demonstrate by the fabrication of gold nanocrescent arrays via colloidal lithography and silicon nanopillar arrays via metal-assisted chemical etching.<br

Surface-Plasmon- And Green-Light-Induced Polymerization in Mesoporous Thin Silica Films - John, Daniel; Mohammadi, Reza; Vogel, Nicolas; Andrieu-Brunsen, Annette (Langmuir, 2020)
The near-field of surface plasmon resonances at planar metal surfaces is confined to the nanoscale, but its resonance wavelength is located in the visible light range, making it interesting for confining polymer functionalization of surfaces but incompatible with the majority of polymerization reactions. Here, fluorescein as a polymerization initiator allowing dye-sensitized polymerization with green light (438-540 nm) is demonstrated to allow polymer functionalization of mesoporous films deposited onto planar silver metal layers. The fluorescein-induced polymer functionalization of mesoporous silica films is investigated with respect to the influence of irradiation power and irradiation time and its potential to generate polymer gradients. Finally, the polymer functionalization of mesoporous films upon surface-plasmon-initiated polymerization is demonstrated. Polymer functionalization thereby determines pH-responsive ionic mesopore accessibility. Consequently, these results present a sound basis for further nanoscale near-field-induced polymer functionalization of porous films.
CRIS-Team Scopus Importer:2020-03-06

Surface-specific visible light luminescence from composite metal oxide nanocrystals - Sternig, Andreas; Bernardi, Johannes; Mckenna, Keith; Diwald, Oliver (Journal of Materials Science, 2015)
Low-coordinated surface elements on metal oxide nanoparticles represent the basis for a new concept of luminescent nanoparticles made of abundant, non-toxic, and thermally stable materials. This combined experimental and theoretical study describes the generation and stability of Ba-doped MgO nanoparticle surfaces and their optical absorption and luminescence dependence on Ba loading. It is demonstrated that the vapor phase growth process employed here represents a particularly robust synthesis approach for particle powders with reproducibly adjustable photoluminescence emission properties in the range between blue and yellow light. Moreover, this in-depth characterization also provides an understanding of the electronic and optical characteristics of this nanoparticulate material with a so far unnoticed potential for solid-state light applications that are based on down conversion of UV ligh

Surrogate Modeling for Control of Microbial Biopolymer Production Process - Dürr, Robert; Otto, Eric; Kok, Rudolph L.; Duvigneau, Stefanie; Kienle, Achim; Bück, Andreas (IFAC-PapersOnLine, 2025)
In this contribution, the Dynamic Mode Decomposition with control (DMDc) is used to derive a surrogate model of a continuous PHA biopolymer production process based on a recently published complex process model. Here, snapshot simulation data of the original model is processed to obtain a linear surrogate model formulation using delay coordinates. The quality of the surrogate is statistically validated within simulation studies. Additionally, the influence of the of the order of delay coordinates is investigated. It is shown, that the highly nonlinear dynamics of the PHA-manufacturing process can be approximated accurately by the DMD-based model even for large variations of initial conditions and control variables. This offers the opportunity to apply well-studied and established tools from robust and optimal control in future investigations.
CRIS-Team Scopus Importer:2025-04-18
Keywords: Black-Box-Identification; Dynamic Mode Decomposition; Polymerisation; Surrogate Modeling

Suspension- and powder-based derivation of Hansen dispersibility parameters for zinc oxide quantum dots - Süß, Sebastian; Lin, Wei; Getmanenko, Olga; Pflug, Lukas; Sobisch, Titus; Peukert, Wolfgang; Lerche, Dietmar; Segets, Doris (Particuology, 2019)
For most particle-based applications, formulation in the liquid phase is a decisive step, and thus, particle interactions and stability in liquid media are of major importance. The concept of Hansen solubility parameters (HSP) was initially invented to describe the interactions of (polymer) molecules and their solubility in different liquids and is increasingly being used in particle technology to describe dispersibility. Because dispersions are not thermodynamically stable, the term Hansen dispersibility parameters (HDP) is used instead of HSP (Süß, Sobisch, Peukert, Lerche, & Segets, 2018). Herein, we extend a previously developed standardized and non-subjective method for determination of Hansen parameters based on analytical centrifugation to the important class of quantum materials. As a technically relevant model system, zinc oxide quantum dots (QDs) were used to transfer our methodology to nanoparticles (NPs) with sizes below 10 nm. The results obtained using the standard procedure starting from a dried powder were compared with those obtained through redispersion from the wet sediment produced during the typical washing procedure of QDs, and drying was observed to play an important role. In conclusion, our study reveals the high potential of HDP for quantifying the interfacial properties of NPs as well as their link to dispersibility.
CRIS-Team Scopus Importer:2019-05-09
Keywords: Colloidal stability; Functionalization; Hansen solubility parameter; Quantum material; Semiconductor nanoparticles

Sustainable Repellent Coatings Based on Renewable Drying and Nondrying Oils - Dehm, Katharina; Walter, Teresa; Weichselgartner, Matthias; Crisp, Ryan; Wommer, Kirsten; Aust, Martin; Vogel, Nicolas (Advanced Materials Interfaces, 2022)

Switching light with light – Advanced functional colloidal monolayers - Vogel, Nicolas; et al. (Nanoscale, 2014)

Synergistic effect in Tragacanth Gum-Ceftriaxone hybrid system as an environmentally friendly corrosion inhibitor for mild steel in acidic solutions - Barrodi, Mohammad Reza; Mirzaee, Ali; Kafashan, Azade; Zahedifard, Sina; Majidi, Hoomaan Joz; Davoodi, Ali; Hosseinpour, Saman (Materials Today Communications, 2023)
An environmental-friendly, economical, and easy to fabricate hybrid inhibitor of Tragacanth Gum (TG) and Ceftriaxone (Cef) is introduced for corrosion prevention of mild steel in HCl solution. A thorough experimental characterization of the inhibitors and their interactions with the mild steel is performed by a combination of Fourier transformation infrared spectroscopy, UV-Vis spectroscopy, and scanning electron microscopy analysis. Electrochemical measurements are utilized to determine the optimum concentration of TG, Cef, and TG-Cef hybrid systems with the highest corrosion protection efficiency. The inhibition efficiency of TG, Cef, and TG-Cef at their optimum concentration (600, 400, and 250 ppm) are 92%, 94%, and 98%, respectively. The TG-Cef hybrid system exhibits the highest corrosion protection efficiency at the lowest concentration, indicating the synergic effect in the TG-Cef hybrid system for the corrosion protection of mild steel. The impact of temperature on the corrosion inhibition of TG-Cef is also studied in the 298–328 K range, revealing a decreasing trend in the corrosion inhibition efficiency of TG-Cef with increasing temperature. The adsorption mechanism and most stable adsorption configuration in each system are determined using quantum chemical calculation and molecular dynamic (MD) simulation indicating both physisorption and chemisorption of the inhibitors.
CRIS-Team Scopus Importer:2023-02-03
Keywords: Ceftriaxone; Electrochemical impedance spectroscopy; Hybrid green corrosion inhibition; Molecular dynamic; Tragacanth gum

Synergistic effect of a crystal modifier and screw dislocation step defects on the formation mechanism of nickel micro-nanocone - Rahimi, Ehsan; Rafsanjani-Abbasi, Ali; Imani, Amin; Kiani Rashid, Ali Reza; Hosseinpour, Saman; Davoodi, Ali (Materials Letters, 2019)
Keywords: Crystal modifier; Step edge; DFT and Monte Carlo simulations; Screw dislocation

Synergy of Catechol-Functionalized Zinc Oxide Nanorods and Porphyrins in Layer-by-Layer Assemblies - Burger, Alexandra; Kunzmann, Andreas; Costa, Ruben Dario; Srikantharajah, Rubitha; Peukert, Wolfgang; Guldi, Dirk Michael; Hirsch, Andreas (Chemistry - A European Journal, 2018)
Catechol-functionalized, positively charged ZnO nanorods (NRs) and anionic porphyrins were integrated into layer-by-layer (LbL) assemblies. In general, this study focuses on the impact that different porphyrins, varying in size and number of negative charges, exert on the LbL architecture in terms of morphology and spectroscopy. In particular, through a combination of analytical methods, including UV/Vis spectroscopy, SEM, and profilometry, valuable insights into LbL assembly formation were gathered. A key feature was the surface coverage in the resulting films. Denser films and surface coverages were realized when highly negatively charged and sterically demanding porphyrins were employed. As a complement to basic characterization, the LbL assembled films were used to fabricate proof-of-concept solar cells.
Keywords: porphyrins; solar energy conversion; layer-by-layer assemblies; layered compounds; thin films; ZnO nanorods

Synthesis and Aggregation of In2O3 Nanoparticles: Impact of Process Parameters on Stoichiometry Changes and Optical Properties - Siedl, Nicolas; Gügel, Philipp; Diwald, Oliver (Langmuir, 2013)
Metalorganic chemical vapor synthesis provides agglomerated In2O3 nanoparticles with a low abundance of particleparticle interfaces. Via exposure to bulk water and subsequent dehydration treatment these powders can be transformed into networks of aggregated nanoparticles. Two major effects arise from the associated emergence of particleparticle interfaces: an enhanced susceptibility to annealing induced n-type doping and a significant red-shift of the optical absorption threshold by 0.2 eV. On the basis of control experiments with pure water, we further explored the impact of the environmental gas atmosphere during annealing on the integral ensemble properties. We found that residual water vapor promotes the mutual attraction of particles, facilitates their condensation, and generates particleparticle interfaces. This work may prove to be of great value for the reproducible production and formulation of percolating metal oxide nanoparticle networks with high control over particle aggregation state, on the one hand, and n-type conductivity as well as optical properties, on the other.

Synthesis and characterization of manganese containing mesoporous bioactive glass nanoparticles for biomedical applications - Nawaz, Qaisar; Ur Rehman, Muhammad Atiq; Burkovski, Andreas; Schmidt, Jochen; Beltran, Ana M.; Shahid, Ameen; Alber, Nina K.; Peukert, Wolfgang; Boccaccini, Aldo R. (Journal of Materials Science: Materials in Medicine, 2018)
Mesoporous bioactive glass (BG) nanoparticles based in the system: SiO2-P2O5-CaO-MnO were synthesized via a modified Stober process at various concentrations of Mn (0-7 mol %). The synthesized manganese-doped BG nanoparticles were characterized in terms of morphology, composition, in vitro bioactivity and antibacterial activity. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis confirmed that the particles had spherical morphology (mean particle size: 110 nm) with disordered mesoporous structure. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of Mn, Ca, Si and P in the synthesized Mn-doped BG particles. Moreover, X-ray diffraction (XRD) analysis showed that Mn has been incorporated in the amorphous silica network (bioactive glass). Moreover, it was found that manganese-doped BG particles form apatite crystals upon immersion in simulated body fluid (SBF). Inductively coupled plasma atomic emission spectroscopy (ICP-OES) measurements confirmed that Mn is released in a sustained manner, which provided antibacterial effect against Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus. The results indicate that the incorporation of Mn in the bioactive glass network is an effective strategy to develop novel multifunctional BG nanoparticles for bone tissue engineering.

Synthesis and characterization of manganese containing mesoporous bioactive glass nanoparticles for biomedical applications - Nawaz, Qaisar; Ur Rehman, Muhammad Atiq; Burkovski, Andreas; Schmidt, Jochen; Shahid, Ameen; Peukert, Wolfgang; Boccaccini, Aldo R. (Journal of Materials Science: Materials in Medicine, 2018)
Mesoporous bioactive glass (BG) nanoparticles based in the system: SiO2–P2O5-CaO-MnO were synthesized via a modified Stöber process at various concentrations of Mn (0-7 mol%). The synthesized manganese-doped BG nanoparticles were characterized in terms of morphology, composition, in vitro bioactivity and antibacterial activity. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis confirmed that the particles had spherical morphology (mean particle size: 110 nm) with disordered mesoporous structure. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of Mn, Ca, Si and P in the synthesized Mn-doped BG particles. Moreover, X-ray diffraction (XRD) analysis has shown that Mn has been incorporated into the amorphous silica network (bioactive glass). More over, it was found that manganese-doped BG particles form apatite crystals upon being immersed in simulated body fluid (SBF). Inductively coupled plasma atomic emission spectroscopy (ICP-OES) measurements confirmed that Mn is released in a sustained mannerBacillus subtilis , Pseudomonas aeruginosaaeruginosa Staphylococcus aureus . The multifunctional BG nanoparticles for bone tissue engineering. The results indicate that the incorporation of Mn into the bioactive glass network is effective. and <br

Synthesis and characterization of zinc oxide nanoparticles for dye-sensitized solar cells - Peukert, Wolfgang; Guldi, Dirk Michael; Hirsch, Andreas; Werner, Fabian; Gnichwitz, Jan-Frederik; Marczak, Renata (2008 AIChE Annual Meeting, AIChE 100, 2008)
Stable ZnO nanoparticles suitable for further derivatization of their surface were synthesized in the liquid phase from homogeneous ethanolic solutions of the precursors, lithium hydroxide and zinc acetate. The particle growth was monitored by in situ absorption spectroscopy and dynamic light scattering (DLS). It was found that the growth of the particles was governed by temperature as well as the presence of the reaction by-product lithium acetate during the ripening process. In particular, the reaction could be almost completely arrested by removal of this by-product. The "washing" consisted of repeated precipitation of the ZnO particles by addition of alkanes such as heptane, removal of the supernatant, and redispersion in ethanol. The ZnO nanoparticles, before and after "washing", were characterized by absorption spectroscopy, DLS, thermogravimetric analysis (TGA), X-ray powder diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The functionalization of the ZnO nanoparticles with photoactive organic compounds, i.e., 5-(N-(3,4-dihydroxyphenethyl)-2-phenoxyacetamide)-10, 15, 20-(p-tert-butyl-triphenyl)-porphyrinato-zinc and 5-(3,4-dihydroxy-N- phenylbenzamide)-10,15,20-tris(4-tertbutylphenyl)-porphyrinato-zinc, was examined. Mesoporous films of the ZnO nanoparticles suitable for use as electrodes in dye-sensitized solar cells (DSSCs) were prepared by the doctor blade technique. Following sintering the films were sensitized by the dye molecules mentioned above. The morphology of the films was characterized by using scanning electron microscopy (SEM). The current generated during photoelectrochemical measurements of these films was ascribed to an efficient photoinduced electron transfer from the photoexcited porphyrin to the ZnO moiety.
Keywords: functionalization; ZnO; nanoparticle; growth; light; scattering; solar; call

Synthesis of amphiphilic silver nanoparticles in nanoreactors from invertible polyester - Voronov, Andriy; Kohut, Ananiy; Peukert, Wolfgang (Langmuir, 2007)
A silver complex is transformed into amphiphilic nanoparticles at room temperature using nanoreactors formed from an amphiphilic polyester. It takes a few minutes to form silver nanocolloids with a narrow particle size distribution. Developed silver forms a stable dispersion in both polar and nonpolar media. The amphiphilic polyester acts as a reducing and stabilizing agent simultaneously. The size of the synthesized amphiphilic silver nanoparticles depends on the concentration of the invertible polyester and solvent polarity. © 2007 American Chemical Society.

Synthesis of Goethite α-FeOOH Particles by Air Oxidation of Ferrous Hydroxide Fe(OH)2 Suspensions: Insight on the Formation Mechanism - Klupp Taylor, Robin; Encina, Ezequiel Roberto; Distaso, Monica; Taylor, Robin N. Klupp; Peukert, Wolfgang (Crystal Growth & Design, 2015)
Iron oxide and iron oxyhydroxide particles, particularly, the goethite extgreeka-FeOOH phase, are environmentally friendly materials and are used in various technological applications as adsorbents, precursors of Fe powders for magnetic recording media, and pigments. In this work, the formation process of extgreeka-FeOOH by air oxidation of Fe(OH)2 suspensions has been studied. The effects of the air flow rate, as well as of the reactant concentration ratio, R (=[(OH)-]/[Fe(II)]), on the reaction product were analyzed. It has been found that the morphology and the size of the extgreeka-FeOOH particles can be modified by means of the air flow rate. Furthermore, by performing a detailed microscopic analysis of the morphology of the initial, intermediate, and final reaction products, we have obtained evidence of epitaxial growth of extgreeka-FeOOH on the Fe(OH)2 substrate. It is suggested that the similarity between the anion arrangements in both phases facilitates this process. Based on these results, a pathway for the formation of extgreeka-FeOOH in highly alkaline medium is proposed in which the size and shape of the initial Fe(OH)2 particles plays a significant role in the formation the extgreeka-FeOOH particles obtained upon completion of the oxidation process.
EAM Import::2019-03-12
Keywords: Oxidation reactions; Atmospheric chemistry; Suspensions; Anions; Oxidation

Synthesis of In2Se3 and Cu2-xSe Micro- and Nanoparticles with Microwave-Assisted Solvothermal and Aqueous Redox Reactions for the Preparation and Stabilization of Printable Precursors for a CuInSe2 Solar Cell Absorber Layer - Schuster, Matthias; Distaso, Monica; Möckel, Stefan; Künecke, Ulrike; Peukert, Wolfgang; Wellmann, Peter (2015)
Micro- and nanoparticles were synthesized and stabilized in order to process a copper indium diselenide (CISe) solar cell absorber layer. A microwave assisted solvothermal reaction for In2Se3 particles was performed, finding that smaller particles could be obtained in shorter times and at lower temperatures than with a conventional autoclave based solvothermal synthesis. In a second route In2Se3 and Cu2-xSe nanoparticles have been synthesized via aqueous redox reactions and been Zeta potential-stabilized to acquire a nanoparticulate ink. This ink was drop cast in ambient atmosphere and annealed in N-2-atmosphere leading to the formation of CISe at lower temperatures than with state-of-the-art processing routes. (C) 2015 Published by Elsevier Ltd.
Keywords: In2Se3; Cu2-xSe; nanoparticles; microwave; Zeta potential; low temperature; CuInSe2; solar cell

Synthesis of In2Se3 and Cu2-xSe Micro- and Nanoparticles with Microwave-Assisted Solvothermal and Aqueous Redox Reactions for the Preparation and Stabilization of Printable Precursors for a CuInSe2 Solar Cell Absorber Layer - Schuster, Matthias; Distaso, Monica; Möckel, Stefan; Künecke, Ulrike; Peukert, Wolfgang; Wellmann, Peter (Energy Procedia, 2015)
Micro- and nanoparticles were synthesized and stabilized in order to process a copper indium diselenide (CISe) solar cell absorber layer. A microwave assisted solvothermal reaction for In2Se3 particles was performed, finding that smaller particles could be obtained in shorter times and at lower temperatures than with a conventional autoclave based solvothermal synthesis. In a second route In2Se3 and Cu2-xSe nanoparticles have been synthesized via aqueous redox reactions and been Zeta potential-stabilized to acquire a nanoparticulate ink. This ink was drop cast in ambient atmosphere and annealed in N2 -atmosphere leading to the formation of CISe at lower temperatures than with state-of-the-art processing route
Keywords: In2Se3; Cu2-xSe; nanoparticles; microwave; Zeta potential; low temperature; CuInSe2; solar cell

Synthesis of methanol by hydrogenolysis of biobased methyl formate using highly stable and active Cu-spinel catalysts in slurry and gas phase reactions - Haagen, Vera; Iser, Jakob; Schörner, Markus; Weber, Dennis; Franken, Tanja; Wasserscheid, Peter; Schühle, Patrick (Green Chemistry, 2023)
This contribution deals with a new atom efficient two-stage production route for green methanol (MeOH) from biomass that includes biomass conversion to methyl formate (MF)/formic acid (FA) mixtures followed by hydrogenolysis to MeOH. Herein, we focus on the hydrogenolysis step and propose a materials solution to the problem of catalyst corrosion by the acidic MF/FA mixture formed in the previous biomass oxidation step. We show that Cu0.9Al2O4 spinel materials are very effective hydrogenolysis catalysts for the conversion of MA/FA mixtures to MeOH. Compared to commercial catalysts such as CuO/Cr2O3, the spinel material does not contain hazardous chromium compounds or require them during synthesis. Furthermore, this spinel catalyst shows much lower corrosion than known commercial hydrogenolysis catalysts. By using reactive frontal chromatography, nitrogen sorption, IR-ATR and XRD measurements we show, that CuO/MgO/ZnO/Al2O3 and CuO/Cr2O3 suffer from leaching of copper and chromium in the presence of FA due to the formation of mobile metal formate species. In contrast, the strongly fixed nature of copper in the highly ordered crystal structure of our Cu0.9Al2O4 spinel type catalyst leads to exceptional stability in the presence of FA and in continuous hydrogenolysis experiments for more than 110 h time-on-stream.<br

Synthesis of millimeter-sized polymer particles by seeded polymerization and their use as shape-designable liquid marble stabilizer - Asaumi, Yuta; Fujiwara, Junya; Oyama, Keigo; Rey, Marcel; Vogel, Nicolas; Hirai, Tomoyasu; Nakamura, Yoshinobu; Fujii, Syuji (Chemistry Letters, 2020)
Millimeter-sized polystyrene particles coated with a hydrophobic polypyrrole overlayer were successfully synthesized by aqueous chemical oxidative seeded polymerization. The dried particles could efficiently adsorb to the air-water interface and worked as an effective liquid marble stabilizer visible to the naked eye. The shape of the liquid marbles could be controlled by application of external mechanical stress.
CRIS-Team Scopus Importer:2020-11-06
Keywords: Liquid marble; Millimeter; Polymer particle

Synthesis of silicon nanoparticles with a narrow size distribution: A theoretical study - Peukert, Wolfgang; Körmer, Richard; Menz, William; Shekar, Shraddha; Brownbridge, George; Mosbach, Sebastian; Kraft, Markus (Journal of Aerosol Science, 2012)
This work presents a study of the processes involved in synthesis of narrowly distributed silicon nanoparticles from the thermal decomposition of silane. Two models are proposed, one which simultaneously solves the kinetic mechanism of Swihart & Girshick (1999, Journal of Physical Chemistry B 103, 64–76) while adjusting the sintering parameters; and another which adjusts the kinetic and surface growth mechanisms while neglecting coagulation and sintering. The models are applied to simulate the centreline of the hot-wall reactor and process conditions of Körmer et al. (2010, Journal of Aerosol Science 41, 998–1007). Both models are shown to give good agreement with experimental PSDs at a range of process conditions. However, it is reported that an unphysical sintering process is obtained when attempting to use Swihart & Girshick’s kinetic mechanism, while solving for the sintering parameters. The model with adjusted gas-phase and surface growth processes gives better quantitative and qualitative agreement with experimental results. It is therefore recommended that further study into the kinetic and heterogeneous growth mechanisms be conducted in order to better understand the fundamental processes occurring in this hot-wall reactor.
Keywords: synthesis; nanoparticle; thermal; decomposition; sintering; coagulation

Synthesis of silver nanoparticle necklaces without explicit addition of reducing or templating agents - Hanisch, Mathias; Mackovic, Mirza; Taccardi, Nicola; Spiecker, Erdmann; Klupp Taylor, Robin (Chemical Communications, 2012)
Here we report that silver nanoparticle necklaces can be readily formed by treatment of colloidal silica with ammoniacal silver complex solution followed by washing, deposition and ageing. We investigate the morphology of the produced materials and elucidate the key variables that influence this promising new approach to one-dimensional nanostructuring. © The Royal Society of Chemistry 201
Keywords: templating; agent; nano; particle

Synthesis of silver nanoparticles in melts of amphiphilic polyesters - Vasylyev, Serhiy; Damm, Cornelia; Segets, Doris; Hanisch, Mathias; Taccardi, Nicola; Wasserscheid, Peter; Peukert, Wolfgang (Nanotechnology, 2013)
The current work presents a one-step procedure for the synthesis of amphiphilic silver nanoparticles suitable for production of silver-filled polymeric materials. This solvent free synthesis via reduction of Tollens' reagent as silver precursor in melts of amphiphilic polyesters consisting of hydrophilic poly(ethylene glycol) blocks and hydrophobic alkyl chains allows the production of silver nanoparticles without any by-product formation. This makes them especially interesting for the production of medical devices with antimicrobial properties. In this article the influences of the chain length of the hydrophobic block in the amphiphilic polyesters and the process temperature on the particle size distribution (PSD) and the stability of the particles against agglomeration are discussed. According to the results of spectroscopic and viscosimetric investigations the silver precursor is reduced to elemental silver nanoparticles by a single electron transfer process from the poly(ethylene glycol) chain to the silver ion.

Synthesis of stable and surface functionalized nanoparticles in an amphiphilic block copolymer melt - Klaumünzer, Martin; Distaso, Monica; Hübner, Jakob; Kryschi, Carola; Peukert, Wolfgang; Wolfrum, Christian (Technical Proceedings of the 2013 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2013, 2013)
We report on an ultrafast and simple one pot synthesis of noble metal nanoparticles and semiconducting metaloxide nanoparticles with aminoblockcopolymer O,O'-Bis (2-aminopropyl) polypropylene glycol- block-polyethylene glycol- block- polypropylene glycols. No additional organic or anorganic solvents are used during synthesis. For demonstrating the universal application of the amino block copolymer for multiple nanoparticle formation we present exemplary syntheses and their characterizations for the following precursor metal compounds: HAuCl, AgNO and Zn(Ac) .
Keywords: synthesis; particle; functionalization

Tailored Double Emulsions Made Simple - Wang, Junwei; Hahn, Simon; Amstad, Esther; Vogel, Nicolas (Advanced Materials, 2021)
Double emulsions, such as water-in-oil-in-water droplets, are important material platforms for conducting fundamental research and technological applications. To date, well-defined double emulsion droplets consisting of a single water core and a thin oil shell can be exclusively formed with sophisticated microfluidic devices. The fabrication, preparation and operation of such devices is challenging, which reduces the availability of tailored double emulsions to a limited community of experts. Here, we introduce a simple method to produce tailored single-core double emulsions with high yield in large quantities, using a vortex mixer. Utilizing the density difference between the dispersed droplet and the continuous phase, this two-step emulsification method can achieve very small core droplet diameters below ten micrometers and ultra-thin shells with thicknesses below one micrometer. We provide a detailed picture of the formation mechanism and demonstrate that the process can be extended to produce multi-shell and multi-core emulsions. Finally, we demonstrate its application to produce structurally colored colloidal supraparticles with unprecedented uniformity and yield. Our method allows the creation of tailored double emulsions with minimal time, cost, effort and expertise and may widen its application to non-specialized scientific communities. This article is protected by copyright. All rights reserved.
Keywords: double emulsion; low-cost; microfluidics; scale-up; supraparticle

Tailored modification of flow behavior and processability of polypropylene powders in SLS by fluidized bed coating with in-situ plasma produced silica nanoparticles - Gomez Bonilla, Juan Sebastian; Trzenschiok, Holger; Lanyi, Franz; Schubert, Dirk W.; Bück, Andreas; Schmidt, Jochen; Peukert, Wolfgang (30th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2019, 2019)
The processability of selective laser sintering (SLS) powders and the characteristics of the generated parts depend amongst others on the flowability. To increase the flowability, SLS powders are usually functionalized with flowing agents. Flowing agents are typically applied by dry particle coating. The optimization of the process parameters necessary to achieve a homogenous coating avoiding segregation is still empirical. In this contribution, an alternative process to particle dry coating is presented. This process integrates the synthesis of silica nanoparticles via plasma enhanced chemical vapor deposition (PECVD) and coating of polymer host particles in a fluidized bed in a single process. The influence of the treatment time on the packing density and flow behavior of the powders is investigated. Test specimen are produced to assess the influence of the treatment on the processability of the powders and the mechanical properties of the produced parts. © Solid Freeform Fabrication 2019: Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium - An Additive Manufacturing Conference, SFF 2019. All rights reserve
Keywords: Additives; Coatings; Compressive strength; Fluidized bed process; Laser heating; Nanoparticles; Plasma CVD; Plasma enhanced chemical vapor deposition; Polypropylenes; Powders; Selective laser sintering; Silica; Silica nanoparticles; Sintering; Synthesis (chemical); Alternative process; Dry-particle coating; Fluidized bed coating; Homogenous coatings; Packing density; Process parameters; Selective laser sintering (SLS); Fluidized beds

Tailoring particle size through nanoparticle precipitation - Peukert, Wolfgang; Schwarzer, Hans-Christoph (Chemical Engineering Communications, 2004)
Precipitation of nanoscaled particles and the size-determining precipitation parameters are investigated experimentally as well as numerically using barium sulfate as a reference substance. The objective of this work is to successfully understand and predict precipitation kinetics. Optimization and tailoring of product properties to specific needs would then be possible without the need of extensive experimentation and its costs. Special attention is paid to the influences of mixing as well as stabilization on the formed PSID. To simulate particle formation the population balance equation, including the terms for nucleation, growth, and agglomeration, is coupled with an specially developed extended version for equi-volumetric mixing of the Engulfment-Deformation-Diffusion-model of micromixing of Baldyga and Bourne (1999). The proposed predictive model for nanoparticle precipitation is explained in detail and simulation results are presented, discussed, and compared to experimental results. © Taylor and Francis Inc.
UnivIS-Import:2015-03-09:Pub.2004.tech.ITC.mechve.tailor
Keywords: Barium sulfate; Micromixing; Nanoparticle; Particle size distribution; Population balance; Precipitation

Tailoring re-entrant geometry in inverse colloidal monolayers to control surface wettability - Utech, Stefanie; Bley, Karina; Aizenberg, Joanna; Vogel, Nicolas (Journal of Materials Chemistry A, 2016)
Controlling the microscopic wetting state of a liquid in contact with a structured surface is the basis for the design of liquid repellent as well as anti-fogging coatings by preventing or enabling a given liquid to infiltrate the surface structures. Similarly, a liquid can be confined to designated surface areas by locally controlling the wetting state, with applications ranging from liquid transport on a surface to creating tailored microenvironments for cell culture or chemical synthesis. The control of the wetting of a low-surface-tension liquid is substantially more difficult compared to water and requires surface structures with overhanging features, known as re-entrant geometries. Here, we use colloidal self-assembly and templating to create two-dimensional nanopore arrays with tailored re-entrant geometry. These pore arrays, termed inverse monolayers, are prepared by backfilling a sacrificial colloidal monolayer with a silica sol-gel precursor material. Varying the precursor concentration enables us to control the degree to which the colloids are embedded into the silica matrix. Upon calcination, nanopores with different opening angles result. The pore opening angle directly correlates with the re-entrant curvature of the surface nanostructures and can be used to control the macroscopic wetting behavior of a liquid sitting on the surface structures. We characterize the wetting of various liquids by static and dynamic contact angles and find correlation between the experimental results and theoretical predictions of the wetting state based on simple geometric considerations. We demonstrate the creation of omniphobic surface coatings that support Cassie–Baxter wetting states for liquids with low surface tensions, including octane ( extgreekg = 21.7 mN m-1). We further use photolithography to spatially confine such low-surface-tension liquids to desired areas of the substrate with high accuracy.

Tailoring the properties of micro-particles for industrial applications using dry powder coating - Wirth, Karl-Ernst; Linsenbühler, Markus (Proceedings International Conference for Particle Technology, 2004)
In industry there is a rising demand for fine powders, e.g. for powder coatings or pharmaceutical applications like enhanced dry powder inhalers. However, the processing of fine-grained particles with diameters between 1 and 10 microns is difficult due to strong van-der-Waals attraction forces. With increasing finess of the particles, the van-der-Waals force between the particles increases in comparison to the gravity force. This effect causes the particles to agglomerate or to stick to surfaces. In order to improve the handling properties, the fine-grained particles (host-particles) are coated with various nano-particles (guest-particles). This process can be conducted in various liquids because the attraction forces between the particles are reduced and various effects can be used to tailor the properties of the coated host-particles. By the surface coating both the flow characteristics and other physical properties like solubility and adsorption parameters are changed. The modified properties depend on the coating process and the properties of the host- and guest-particles. By parameter variations the properties of the composite particles, i.e. the coated host-particles, can be systematically adjusted to the requirements of industrial applications. The changed particle-particle interactions can be tested using an atomic force microscope for measuring single-particle forces and both a laboratory bubbling fluidized bed and/or a shear cell to describe the bulk properties. The last mentioned tests describe the silo storage behavior or the conveying behavior of the tailor-made composites, respectively. Changed physical properties can be characterized using both adsorption and solubility tests. The appropriate particle processing and the changed physical properties of the tailor-made particles as well as the methods to characterize the tailor-made functionalized micro-particles are given. The main focus of the presented research is based on the solubility behavior of the tailor-made composite particles.
UnivIS-Import:2015-04-16:Pub.2004.tech.ITC.mechve.proper
Keywords: powder; particle; coating

Tailoring the Reaction Pathway for Control of Size and Composition of Silver-Gold Alloy Nanoparticles - Traore, Nabi; Berthold, Michelle; Hartmann, Lukas; Schmul, Patricia; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Peukert, Wolfgang (Journal of Physical Chemistry C, 2024)
In this work, we independently tune both the particle size and the chemical composition of bimetallic silver−gold alloy nanoparticles (NPs) by carefully controlling the reaction pathway. NP synthesis involves control of the supersaturation profile in time and space. For the reaction-controlled case, this supersaturation profile is determined by a network of reactions leading to the buildup of the monomer concentration. Using a variety of characterization tools, we show how the process conditions influence the coupled reactions in the complex formation mechanism of Ag−Au alloy NPs. Applying a simple mass balance allows for the independent control of size and chemical composition of these NPs, yielding particles with constant composition and varying size in the range of 20 to 40 nm. A series of constant sizes and varying chemical compositions in the range of 10% to 100% molar gold content is also possible. Our new methodology shows an example of how reaction networks can be tailored to achieve targeted NP properties and paves the way for better control in the synthesis of multicomponent NPs.<br

Targeted color design of silver-gold alloy nanoparticles - Traore, Nabi; Spruck, Christina; Uihlein, Andrian; Pflug, Lukas; Peukert, Wolfgang (Nanoscale Advances, 2023)
This research article focuses on the targeted color design of silver-gold alloy nanoparticles (NPs), employing a multivariate optimization approach. NP synthesis involves interconnected process parameters, making independent variation challenging. Data-based property-process relationships are established to optimize optical properties effectively. We define a color target, employ a green chemical co-reduction method at room temperature and optimize process parameters accordingly. The CIEL*a*b* color space (Commission Internationale de l'Éclairage - International Commission on Illumination) and Euclidean distances facilitate accurate color matching to establish the property-process relationship. Concurrently, theoretical Mie calculations explore the structure-property relationship across particle sizes, concentrations, and molar gold contents. The theoretically optimal structure agrees very well with experimental particle structures at the property-process relationship's optimum. The data-driven property-process relationship provides valuable insights into the formation mechanism of a complex particle system, sheds light on the role of relevant process parameters and allows to evaluate the practically available property space. Model validation beyond the original grid demonstrates its robustness, yielding colors close to the target. Additionally, Design of Experiments (DoE) methods reduce experimental work by threefold with slight accuracy trade-offs. Our novel methodology for targeted color design demonstrates how data-based methods can be utilized alongside structure-property relationships to unravel property-process relationships in the design of complex nanoparticle systems and paves the way for future developments in targeted property design.
CRIS-Team Scopus Importer:2023-12-22

Temperature characteristics in a flash atomization process - Günther, Astrid; Bräuer, Andreas; Siegler, Philipp; Köninger, Benedikt; Wirth, Karl-Ernst (Atomization and Sprays, 2016)

Temperature influence on the triboelectric powder charging during dry coating of polypropylene with nanosilica particles - Düsenberg, Björn; Tischer, Florentin; Valayne, Erika; Schmidt, Jochen; Peukert, Wolfgang; Bück, Andreas (Powder Technology, 2022)
The influence of process temperature on the triboelectric charge during dry coating of cohesive polymer powders is investigated. The purpose of heating is to decrease the surface moisture of the powder, which results in an increase of electrical charge of the powder. The effect of the hydrophilicity of the SiO2 guest particles on the quality of the dry coating of PP host particles was investigated with respect to the integral charge of the dry coated powder. Furthermore, the flowability, crystallization behavior and degree of coverage (DOC) were investigated to determine the influence of the increased charge on these topics. Increased process temperature increases the electrical charge of the powder, which leads to a higher DOC with guest particles and, thus, drastically improved flowability compared to dry coating at ambient temperature. Furthermore, changes in the crystallization behavior of polypropylene are observed, due to more nuclei.
CRIS-Team Scopus Importer:2022-03-25
Keywords: Crystallization; Dry coating; Flowability; Mixing; Polymer; Thermal treatment; Triboelectricity

Template-free structuring of colloidal hetero-monolayers by inkjet printing and particle floating - Vogel, Nicolas; et al. (Soft Matter, 2010)
Here we demonstrate the feasibility of a novel approach to simultaneously pattern surfaces with heterogeneous colloidal monolayers on various length scales from tens of mm down to nanometres by a combination of simple inkjet printing and nanosphere lithography. The process involves inkjet printing of different particle types in a pre-pattern with sparsely distributed particles on an initial substrate. After immersion in water the particles float off the substrate and self-assemble into a dense and hexagonally ordered colloidal monolayer, with a concomitant 1D contraction of the pre-pattern along the immersion direction. While nanosphere lithography yields the nanostructures, the superimposed mm scale pattern is defined by the inkjet printing process, leading to hexagonally ordered colloidal monolayers of various particles sizes or materials in parallel. Since the mu m pattern with arbitrary shape is simply designed on a computer and printed, the process does not require any customized template or mask to be fabricated. Due to its simplicity the computer-assisted method shows great potential for automatization, which should substantially improve structure quality and turn it into a technologically promising approach.

TEM preparation method for site- and orientation-specific sectioning of individual anisotropic nanoparticles based on shadow-FIB geometry - Vieweg, Benito; Butz, Benjamin; Peukert, Wolfgang; Klupp Taylor, Robin; Spiecker, Erdmann (Ultramicroscopy, 2012)
For the comprehensive characterization of nanoparticles cross-sectional investigation on the atomic scale by analytical and high-resolution transmission electron microscopy (TEM) is indispensable. Cross-sectioning is especially important for anisotropic nanoparticles to gain information on structure and chemistry along all important projections. We present a focused ion beam (FIB) method for site- and orientation-specific cross-sectioning of arbitrary nanoparticles that are dispersed on a substrate. By adopting a shadow geometry originally developed for thin sensitive films' protection of the specimen by a platinum layer is avoided. This enables simultaneous observation (from the front side) by the electron beam and ion-beam sectioning (from the back side of the supporting substrate) of individually selected particles with excellent accuracy on the nanometer scale. The feasibility and general applicability of the method is demonstrated by site-specific sectioning and cross-section HRTEM investigation of two types of anisotropic nanostructures: silver nanorods with five-fold twin structure and Janus-type silver patchy particles. © 2011 Elsevier B.V.
Keywords: FIB; High-resolution transmission electron microscopy; Nanoparticles; Nanorods; Patchy particles; TEM preparation

The Beginner's Guide to Chiral Plasmonics: Mostly Harmless Theory and the Design of Large-Area Substrates - Görlitzer, Eric; Puri, Aniket S.; Moses, Jebin J.; Poulikakos, Lisa V.; Vogel, Nicolas (Advanced Optical Materials, 2021)
Chiral plasmonics is a fascinating research field that is attractive to scientists from diverse backgrounds. Physicists study light–matter interactions, chemists seek ways to analyze enantiomeric molecules, biologists study living objects, and material engineers focus on scalable production processes. Successful access to this emergent field for an interdisciplinary community depends on overcoming three main issues. First, understanding the physical background of chiral plasmonics requires proper introduction in easy language. Second, pitfalls in the characterization of chiroplasmonic features can prevent accurate interpretation. Third, simple and robust methods capable of covering macroscopic substrate areas must be available. This tutorial-style review addresses these issues with the goal to provide a comprehensive introduction into chiral plasmonic nanostructures. It starts with a brief introduction of the relevant physics involved in chiral light−matter interactions. A brief guide about how to adequately characterize samples follows. Subsequently, an overview of fabrication techniques that produce chiral substrates over large areas is given, and the strengths and weaknesses of the different approaches are discussed. The focus is on simple and robust processes that do not require clean room facilities and can be implemented by a much larger scientific audience.
Created from Fastlane, Scopus look-up
Keywords: chirality; colloidal lithography; large-area substrates; plasmonics; surface patterning

The effect of mixing on silver particle morphology in flow synthesis - Yang, Tao; Segets, Doris; Thajudeen, Thaseem; Han, Yongsheng; Peukert, Wolfgang (Chemical Engineering Science, 2018)
Keywords: Anisotropic silver particles; Dendrites; Analytical centrifugation; Mixing time; Plates

The Effect of the Presence of Very Cohesive Geldart C Ultra-Fine Particles on the Fluidization of Geldart A Fine Particle Beds - Marnani, Abbas Kamranian; Bück, Andreas; Antonyuk, Sergiy; Van Wachem, Berend; Thevenin, Dominique; Tomas, Juergen (Processes, 2019)
The effect of the presence of ultra-fines (d < 10 mu m) on the fluidization of a bed containing fine particles (d < 100 mu m), is the subject of this paper. Practically, it can happen due to breakage or surface abrasion of the fine particles in some processes which totally changes the size distribution and also fluidization behaviour. The materials used in this study are both ground calcium carbonate (GCC); fine is CALCIT MVT 100 (Geldart's group A) and ultra-fine is CALCIT MX 10 (group C). The experimental results for different binary mixtures of these materials (ultra-fines have 30%, 50%, or 68% of the total mixture weight) show that the physical properties of the mixtures are close to those of pure ultra-fine powders. Using mean values of the bed pressure drop calculated from several independent repetitions, the fluidization behaviour of different mixtures are compared and discussed. The fluidization behaviour of the mixtures is non-reproducible and includes cracking, channelling and agglomeration (like for pure ultra-fine powders). Increasing the portion of ultra-fine materials in the mixture causes a delay in starting partial fluidization, an increase in the bed pressure drop as well as a delay in reaching the peak point.
CRIS-Team WoS Importer:2019-02-21

The effect of very cohesive ultra-fine particles in mixtures on compression, consolidation, and fluidization - Marnani, Abbas Kamranian; Bück, Andreas; Antonyuk, Sergiy; van Wachem, Berend; Thévenin, Dominique; Tomas, Jürgen (Processes, 2019)
This paper focuses on the effect of ultra-fine (d < 10 μm) powders in mixtures with fine (d < 100 μm) bulk material on compression processes and also evaluates the re-fluidization behavior of the compressed bed (history effect). Achieving this goal, different mixtures of fine and ultra-fine Ground-Carbonate-Calcium were compressed at three pressure levels. The results show that by increasing the applied pressure, the compressibility decreases due to change in compaction regime. Subsequently, for the higher pressure, the slope of packing density versus applied stress curves is noticeably different. However, this slope does not depend on the size distribution of mixtures, but on the type of material. Comparing fluidization and re-fluidization curves (bed pressure drop vs. gas velocity) shows an increase in the maximum bed pressure drop (DPpeak) for re-fluidization. By increasing the portion of ultra-fine particles in the binary mixture, DPpeak increases in a non-linear manner. Furthermore, the incipient fluidization point moves to a higher gas velocity. After compression, the peak of the bed pressure drop in the re-fluidization test happens at a lower gas velocity than in the initial fluidization test. Thus, the slope of the loading curve is much larger for re-fluidization. The opposite is observed for the unloading curves.
CRIS-Team Scopus Importer:2019-07-23
Keywords: Binary mixtures; Compression; Consolidation; Fine and ultra-fine particles; Fluidization; History effect

The effects of post-processing on the surface and the optical properties of copper indium sulfide quantum dots - Akdas, Tugce; Distaso, Monica; Kuhri, Susanne; Winter, Benjamin; Birajdar, Balaji; Spiecker, Erdmann; Guldi, Dirk Michael; Peukert, Wolfgang (Advances in Colloid and Interface Science, 2015)
In the current contribution we report on investigations regarding the surface of CuInS2 quantum dots and on different strategies to control the amount of surface ligands in a post-processing step. In particular, the reactivity of the organic components, that is, 1-dodecanthiol and 1-octadecene as ligand and solvent, respectively, during nanocrystal formation was studied. A new method to remove residuals from the reaction mixture and to detach excess organics from the surface of the nanocrystals is reported. Our new method, which is based on the utilization of acids, is compared with standard purification procedures by means of thermogravimetric analysis (TGA) with particular focus on its efficiency to remove organics. As a complement, the surface chemistry is analyzed by nuclear magnetic resonance spectroscopy (NMR) to shed light on the nature of the organic components still present after purification. Further analysis of the product by inductively coupled plasma optical emission spectroscopy (ICP-OES) is performed to verify the influence of the new purification method on surface composition and properties. Moreover, steady state and time resolved spectroscopies give insights into excitonic behavior as well as recombination processes. Finally, the new method is optimized for the purification of CuInS2-ZnS nanocrystals, which show enhanced optical properties.

The first sixty years of professor Evangelos Tsotsas—or: A quarter-century of combining drying and particle formation - Bück, Andreas; Metzger, Thomas; Schönherr, Michael (Drying Technology, 2019)
CRIS-Team Scopus Importer:2019-05-02

The flow field in the mill - a key factor for the prediction of the comminution result - Epple, Philipp; Breuer, Michael; Peukert, Wolfgang; Toneva, Petya Ivanova; Wirth, Karl-Ernst (AIChE Annual Meeting, Conference Proceedings, 2006)
Measurements of the mean and time dependent velocity profile were obtained for the first time in an air classifier mill using particle image velocimetry (PIV). Detailed measurements in the vicinity of the impact elements and in the region of the internal classifier are presented. Different pin geometries have been studied at various circumferential velocities of the grinding disk and the classifier. Regions with high turbulence have been observed for all investigated pin geometries at the flow off side of the impact element. The classifier velocity doesn't influence the velocity profiles near the impact elements in main flow direction. The velocity profile on the front sight of the impact element, where the comminution process takes place, is constant with time and preserves a characteristic form with varying operational conditions. The one phase flow field in the complete mill geometry has been modelled by CFX.
UnivIS-Import:2015-04-16:Pub.2006.tech.ITC.stmmec.theflo
Keywords: Air classifier mill; CFX; Flow investigations; PIV; Turbulence modeling

The influence of dispersing and stabilizing of indium tin oxide nanoparticles upon the characteristic properties of thin films - Peukert, Wolfgang; Reindl, Armin; Mahajeri, Mahdi; Hanft, J (Thin Solid Films, 2009)
Stable suspensions of indium tin oxide nanoparticles were prepared by dispersing for 1 h in ethanol and stabilizing with 2-[2-(2-Methoxyethoxy)ethoxy]acetic acid. Particle size, morphology, and structure were characterized by a combination of dynamic light scattering, high resolution transmission electron microscopy, and X-ray diffraction. Spin coating of the stable suspensions resulted in densely packed films with a high transparency. Dispersing times exceeding 1 h led to a significant "overdispersing" effect, i.e. an increasing aggregate size of the suspensions was observed. Zeta-potential, pH, and X-ray photoelectron spectroscopy measurements were conducted to achieve a detailed understanding of the effect of "overdispersing". With an increasing time of dispersion, i.e. with a decreasing stability of the suspensions, the thin films fabricated by spin coating displayed an increasing pore size distribution and surface roughness. In addition a strong decrease in transmittance and in conductivity was observed. © 2008 Elsevier B.V. All rights reserved.
Keywords: Conductivity; Dispersion; Indium tin oxide; ITO; Morphology; Nanoparticles; Stability; Thin films; Transmittance

The influence of particle charge and roughness on particle-substrate adhesion - Peukert, Wolfgang; Zhou, Hongben; Götzinger, Martin (Powder Technology, 2003)
In the electrophotographic process, charged toner particles are transferred from the bulk to the photoreceptor drum and from there to the paper. In high performance printing systems, more than 1000 pages/min are printed, equivalent to the transfer of more than 10 particles/min. The key to understand and to improve the printing system is particle-particle and particle-substrate interactions, respectively. We study the adhesion forces by means of atomic force microscopy (AFM) measurements complemented by centrifugal detachment measurements in an ultracentrifuge. The interpretation of AFM measurements requires careful calibration of the used cantilevers together with a sound statistical analysis. Particle charges have been determined from force-displacement curves. Silicon wafers, polished and PVD-coated aluminum substrates with tailored roughness are chosen as model materials. Spherical, smooth polystyrene and specially prepared alumina particles as well as rugged toner particles of irregular shape are investigated. We proceed from well-defined model systems (flat smooth substrate interacting with spherical particles) to technical systems where rugged particles adhere to rough substrates. The adhesion forces consist of electrostatic and of non-electrostatic (e.g. van der Waals forces) components. We show how the influence of electrostatic forces relative to the van der Waals forces can be controlled. © 2003 Elsevier B.V. All rights reserved.
Keywords: Adhesion; AFM; Electrostatic force; Toner

The Influence of Pipe Geometry on the Critical Velocity of Horizontal Pneumatic Conveying of Coarse Particles. - Wirth, Karl-Ernst; Molerus, Otto (Powder Technology, 1985)
With single-phase flow a circular pipe cross-section is optimal, since the ratio of wetted perimeter to cross-sectional area is minimal. Similar arguments also hold good in the case of fully suspended solid loaded flow. Under those circumstances, however, in which in horizontal pipes more or less separation of flow occurs, i.e. in the case of strand flow, one may ask whether pipe profiles other than circular could be more suited. For circular and semicircular pipes with identical cross-sectional areas, theory and experiments yield critical velocities in the semicircular pipe which are about 25% smaller. © 1985.
UnivIS-Import:2015-03-05:Pub.1985.tech.ITC.mechve.theinf
Keywords: flow; fluidization; powder

The influence of suspension properties on the grinding behavior of alumina particles in the submicron size range in stirred media mills - Peukert, Wolfgang; Stenger, Frank; Mende, Stefan; Schwedes, Jörg (Powder Technology, 2005)
The paper shows the possibility to produce alumina nanoparticles in a stirred media mill by an appropriate adjustment of the suspension properties and the milling parameters. Besides a high electrostatic suspension stability that can be realised for metal oxides by means of pH value adjustment small grinding beads favour the production of alumina particles with a median particle size of around 10 nm. In addition to size reduction mechanochemical changes and the formation of alumina hydroxide are detected during wet grinding of alumina. This is analysed by means of X-ray diffraction analysis (XRD), thermogravimetry (TG) and dynamic scanning calorimetry (DSC) measurement and a quantitatively good agreement between the three methods could be obtained. Further, it is proved that the hydroxide produced dissolves at pH values lower than 5 thus influencing the grinding process under these conditions.
Keywords: Mechanochemical effects; Nanosized alumina; Stirred media mill; Suspension properties

The influence of thickness of stearic acid self-assembled film on its protective properties - Hosseinpour, Saman; et al. (Journal of The Electrochemical Society, 2016)

The low Reynolds number turbulent flow and mixing in a confined impinging jet reactor - Schwertfirm, Florian; Gradl, Johannes; Schwarzer, Hans-Christoph; Peukert, Wolfgang; Manhart, Michael (International Journal of Heat and Fluid Flow, 2007)
Turbulent mixing takes an important role in chemical engineering, especially when the chemical reaction is fast compared to the mixing time. In this context a detailed knowledge of the flow field, the distribution of turbulent kinetic energy (TKE) and its dissipation rate is important, as these quantities are used for many mixing models. For this reason we conduct a direct numerical simulation (DNS) of a confined impinging jet reactor (CUR) at Re = 500 and Sc = 1. The data is compared with particle image velocimetry (PIV) measurements and the basic flow features match between simulation and experiment. The DNS data is analysed and it is shown that the flow is dominated by a stable vortex in the main mixing duct. High intensities of turbulent kinetic energy and dissipation are found in the impingement zone which decrease rapidly towards the exit of the CUR. In the whole CIJR the turbulence is not in equilibrium. The strong mixing in the impingement zone leads to a rapid development of a monomodal PDF. Due to the special properties of the flow field, a bimodal PDF is generated in cross-sections downstream the impingement zone, that slowly relaxes under relaminarising conditions. The time required for meso-mixing is dominating the overall mixing performance.
Keywords: direct numerical simulation; confined impinging jet reactor; particle image velocimetry; opposing jets; turbulent mixing

The mass transfer at Taylor cones - Lübbert, Christian; Peukert, Wolfgang (Journal of Aerosol Science, 2018)

The morphology of integrated self-assembled monolayers and their impact on devices – A computational and experimental approach - Novak, Michael; Jäger, Christof; Rumpel, Armin; Kropp, Henning; Peukert, Wolfgang; Clark, Timothy; Halik, Marcus (Organic Electronics, 2010)
We report on a combined experimental and computational study on self-assembled monolayers (SAMs). The dielectric properties of SAMs based on n-alkyl phosphonic acids in large area thin film devices (organic field-effect transistors with good hole mobilities up to 0.3 cm² V−1 s−1 at −1 V and capacitors) depend on their chain length, but not consistently to theoretical pictures of tunneling through saturated n-alkanes. An unexpected saturation of current density with increasing chain length was obtained in devices, what impact on the leakage current in transistors and current density in capacitors. This is attributed to different self-assembled monolayer morphology ranging from an amorphous state for short alkyl chains to a quasi-crystalline state for longer alkyl chains. Molecular dynamics (MD) simulations provide a deeper insight into the nature of the three-dimensional intermolecular interactions and support the proposed SAM morphology. The change in morphology leads to a reduced effective SAM thickness in devices, which could be described by a Simmons approach quantitatively. The morphological aspect of self-assembled molecules is of enormous importance beyond the applications of SAMs in low-voltage, high mobility organic transistors because of it’s relevance for the hole field of molecular scale electronics. It demonstrates that even small changes in the molecular design can change the molecular interactions and monolayer assembly.

The nature of self-assembled octadecylphosphonic acid (ODPA) layers on copper substrates - Zhao, Weijie; Göthelid, Mats; Hosseinpour, Saman; Johansson, Malin B.; Li, Gen; Leygraf, Christofer; Johnson, C. Magnus (Journal of Colloid and Interface Science, 2021)
Hypothesis: The self-assembly of amphiphilic molecules onto solid substrates can result both in the formation of monolayers and multilayers. However, on oxidized and non-oxidized copper (Cu), only monolayer formation was reported for phosphonic acids possessing one phosphate head group. Here, the adsorption of octadecylphosphonic acid (ODPA) on Cu substrates through a self-assembly process was investigated with the initial hypothesis of monolayer formation. Experiments: The relative amount of ODPA adsorbed on a Cu substrate was determined by infrared reflection/absorption spectroscopy (IRRAS) and by atomic force microscopy (AFM) investigations before and after ODPA deposition. X-ray photoelectron spectroscopy (XPS) with sputtering was used to characterize the nature of the layers. Findings: The results show that the thickness of the ODPA layer increased with deposition time, and after 1 h a multilayer film with a thickness of some tens of nm was formed. The film was robust and required long-time sonication for removal. The origin of the film robustness was attributed to the release of Cu ions, resulting in the formation of Cu-ODPA complexes with Cu ions in the form of Cu(I). Preadsorbing a monolayer of octadecylthiol (ODT) onto the Cu resulted in no ODPA adsorption, since the release of Cu(I) ions was abolished.
CRIS-Team Scopus Importer:2020-08-28
Keywords: Atomic force microscopy; Copper leaching; Infrared reflection/absorption spectroscopy; Octadecylphosphonic acid; Self-assembled monolayers; X-ray photoelectron spectroscopy

The Optical Janus Effect: Asymmetric Structural Color Reflection Materials - England, Grant T.; Russell, Calvin; Shirman, Elijah; Kay, Theresa; Vogel, Nicolas; Aizenberg, Joanna (Advanced Materials, 2017)
Structurally colored materials are often used for their resistance to photobleaching and their complex viewing-direction-dependent optical properties. Frequently, absorption has been added to these types of materials in order to improve the color saturation by mitigating the effects of nonspecific scattering that is present in most samples due to imperfect manufacturing procedures. The combination of absorbing elements and structural coloration often yields emergent optical properties. Here, a new hybrid architecture is introduced that leads to an interesting, highly directional optical effect. By localizing absorption in a thin layer within a transparent, structurally colored multilayer material, an optical Janus effect is created, wherein the observed reflected color is different on one side of the sample than on the other. A systematic characterization of the optical properties of these structures as a function of their geometry and composition is performed. The experimental studies are coupled with a theoretical analysis that enables a precise, rational design of various optical Janus structures with highly controlled color, pattern, and fabrication approaches. These asymmetrically colored materials will open applications in art, architecture, semitransparent solar cells, and security features in anticounterfeiting materials.
Keywords: absorption; multilayers; photonic crystals; structural color; thin films

Theoretical and experimental investigations on sintering kinetics of silica nanoparticles - Peukert, Wolfgang; Schmid, Hans-Joachim; Kirchhof, Martin; Förster, Henning (2006 AIChE Spring National Meeting - 5th World Congress on Particle Technology, 2006)
The sintering kinetics of single silica nanoparticle contacts in the gas phase is investigated experimentally and theoretically. Experiments are conducted in a high-temperature short-time flow reactor allowing for precise control of temperature and residence time. Sintering experiments have been conducted for temperatures up to 1600 °C and residence times down to 5 ms. Results show significantly shorter sintering times than predicted by macroscopic sintering models. For vitreous materials such as silica the predominant sintering mechanism is supposed to be viscous flow. Therefore, three dimensional simulations of the sintering process have been conducted by solving the free surface viscous flow process using a volume-of-fluid (VOF) method. Additionally, van der Waals interactions have been considered as momentum source. The results suggest that molecular van der Waals interactions have great influence on the sintering kinetics of nanoparticles which is insufficiently described by macroscopic models.
Keywords: Silica; Sintering; Viscous flow; Volume-of-fluid method (VOF)

The Properties of Iron Oxide Nanoparticle Pigments - Klupp Taylor, Robin (Metal oxide nanoparticles - Formation, functional properties, and interfaces, 2021)

The relevance of interactions in nanoparticulate systems - Peukert, Wolfgang (World Congress Particle Technology 4, 2002)
In the field of Particle Technology, processes cannot yet be designed from basic molecular understanding. Nanotechnology, however, begins to bridge this gap between molecules and particles and may thus open up new ways not only for the production and handling of particulate matter but also for the engineered design of advanced material properties. The visions and applications in nanoparticle technology cover a broad range, for instance quantum dots in information technology, refractory particles for advanced ceramics, highly active substances in pharmacy, catalysts or micro- and mesoporous adsorbents, to name only a few applications. Starting from the concept of product engineering, we investigate the basic preconditions for tailoring nanoparticulate properties, i.e. the control of the particle interactions. This concept is then applied to particulate thin film formation as an example of structure formation. The structure of dip-coated samples, defined as the order of particles within the layer, was found to vary with the pH and the ion concentration adjusted in the sol bath. It was observed that the surface roughness scanned by an atomic force microscope increased with increasing electrolyte concentration. The structural evolution of the particulate network was studied by measuring the viscosity as a function of shear rate and solid concentration. Finally, the influence of coating structures on the transmission properties was determined. Especially in the case of LaCl3 a strong dependence was observed. The results explicitly confirm a correlation between microscopic structure and macroscopic propertie
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.therel_5
Keywords: nanotechnology; particle; interaction

The relevance of particle interactions in nanoparticulate systems - Application to particulate thin films - Günther, Lydia; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2002)
In the field of Particle Technology, processes cannot yet be designed from basic molecular understanding. Nanotechnology, however, begins to bridge this gap between molecules and particles and may thus open up new ways not only for the production and handling of particulate matter but also for the engineered design of advanced material properties. The visions and applications in nanoparticle technology cover a broad range, for instance quantum dots in information technology, refractory particles for advanced ceramics, highly active substances in pharmacy, catalysts or micro- and mesoporous adsorbents, to name only a few applications. Starting from the concept of product engineering, we investigate the basic preconditions for tailoring nanoparticulate properties, i.e. the control of the particle interactions. This concept is then applied to particulate thin film formation as an example of structure formation. The structure of dip-coated samples, defined as the order of particles within the layer, was found to vary with the pH and the ion concentration adjusted in the sol bath. It was observed that the surface roughness scanned by an atomic force microscope increased with increasing electrolyte concentration. The structural evolution of the particulate network was studied by measuring the viscosity as a function of shear rate and solid concentration. Finally, the influence of coating structures on the transmission properties was determined. Especially in the case of LaCl3 a strong dependence was observed. The results explicitly confirm a correlation between microscopic structure and macroscopic properties.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.therel

Thermal rounding for shape modification of high-performance polyetherketoneketone and reinforced polyetherketoneketone-carbon fiber composite particles - Unger, Laura; Fischer, Sybille; Sesseg, Jens P. W.; Pfister, Andreas; Schmidt, Jochen; Bück, Andreas (Journal of Polymer Research, 2023)
This study presents shape transformation of anisotropic high-performance thermoplastic polyetherketoneketone (PEKK) and carbon fiber reinforced powder composite particles (HT-23) by thermal rounding. The shape transformation is achieved by (partial) melting of the high-temperature thermoplast microparticles. Three different process setups are presented, investigating the impact of the source of heat supply on the resulting shape modification: using a directly heated sheath gas flow, an indirect heat supply through the reactor wall and a combined approach. Regardless of the chosen setup, a modification of the particle shape was observable. The most advantageous shape transformation was observed in the indirect heating approach. In addition, the enhanced shape transformation yields an improved free flow behaviour of the powders, as quantified by ring-shear experiments. Reductions of the unconfined yield strengths of the powders for high consolidation stresses as high as 18 percent for PEKK and 30 percent for the HT-23 are achieved. Thereby, processability of the powder in laser based powder bed fusion is enhanced, extending the range of available (composite) polymer materials.
CRIS-Team Scopus Importer:2023-06-02
Keywords: Downer reactor; Polyetherketoneketone; Polyetherketoneketone-carbon fiber composites; Spheronization; Thermal rounding

Thermal rounding of micron-sized polymer particles in a downer reactor: direct vs indirect heating - Gomez Bonilla, Juan Sebastian; Dechet, Maximilian; Schmidt, Jochen; Peukert, Wolfgang; Bück, Andreas (Rapid Prototyping Journal, 2020)
Purpose: The purpose of this paper is to investigate the effect of different heating approaches during thermal rounding of polymer powders on powder bulk properties such as particle size, shape and flowability, as well as on the yield of process. Design/methodology/approach: This study focuses on the rounding of commercial high-density polyethylene polymer particles in two different downer reactor designs using heated walls (indirect heating) and preheated carrier gas (direct heating). Powder bulk properties of the product obtained from both designs are characterized and compared. Findings: Particle rounding with direct heating leads to a considerable increase in process yield and a reduction in powder agglomeration compared to the design with indirect heating. This subsequently leads to higher powder flowability. In terms of shape, indirect heating yields not only particles with higher sphericity but also entails substantial agglomeration of the rounded particles. Originality/value: Shape modification via thermal rounding is the decisive step for the success of a top-down process chain for selective laser sintering powders with excellent flowability, starting with polymer particles from comminution. This report provides new information on the influence of the heating mode (direct/indirect) on the performance of the rounding process and particle properties.
CRIS-Team Scopus Importer:2020-08-28
Keywords: Crystallinity; Particle shape; Particle size; Polymers; Powder flowability; Selective laser sintering; Shape modification; Thermal rounding

Thermodynamic characterization of water and alcohol sprays using Raman spectroscopy - Schuster, Julian; Siegler, Philipp; Bräuer, Andreas; Will, Stefan (28th European Symposium on Applied Thermodynamics, 2015)

Thermo‐Optical Analysis of Surface‐ and Volume‐Additivated Polymer Powders for Near‐Infrared Laser Powder Bed Fusion - Sommereyns, Alexander; Schmidt, Jochen; Leong, Cheechau; Tischer, Florentin; Schmidt, Michael (Advanced Photonics Research, 2025)
Near-infrared laser sources have the potential to change the process dynamics in laser powder bed fusion of polymers. To take full advantage of the shorter processing laser wavelength, the addition of absorbing additives, such as carbon black nanoparticles, becomes inevitable. Many nanoparticle characteristics can influence the laser-material interaction, such as quantity, dispersion, and position relative to the polymer matrix, but have not been investigated under processing conditions. Therefore, this study improves the understanding of the optical material properties present in laser powder bed fusion by quantifying the thermo-optical properties of PA11 powder, melt and solid, additivated with minute amounts of carbon black nanoparticles on the surface and throughout the volume of the particles. Surface-additivation results in the highest increase in laser attenuation overall and creates a segregated network that acts as a barrier to laser penetration in the molten and solid state. By contrast, the random distribution of agglomerated nanoparticles throughout the particle volume allows most of the laser radiation to pass through. Other nanoparticle effects, such as thermal stabilization and crystal formation, affect the volume-additivated particles the most. The thermo-optical results are complemented by analysis of process-relevant powder, thermal, structural, and compositional material propertie
Keywords: attenuation coefficient; carbon black; dry coating; laser powder bed fusion; matrix incorporation; polymer nanocomposites; thermo-optical characterization

The role of Ca/Zr ratio on the local structure and phase transitions in lead-free (Ba,Ca)(Zr,Ti)O3 - Dobesh, David; Gadelmawla, Ahmed; Miyazaki, Hidetoshi; Hinterstein, Manuel; Kimura, Koji; Maier, Juliana; Banerjee, Semanti; Zeair, Omar; Mehta, Sharly; da Silva, Lucas Lemos; Khansur, Neamul Hayet; Hayashi, Koichi; et al. (Journal of the European Ceramic Society, 2024)
In this study, the structural phase transitions are investigated as a function of composition and temperature for polycrystalline x(Ba0.7Ca0.3)TiO3-(1 − x)Ba(Zr0.2Ti0.8)O3 (x = 0.40, 0.45, 0.50, 0.55, and 0.60) through a combination of Raman spectroscopy, synchrotron X-ray diffraction, and dielectric spectroscopy. The aim is to gain insight into the complex phase boundary region responsible for the excellent electromechanical properties. The results demonstrate the correlation between local site substitutions based on the stoichiometric variations to the microstructure and dielectric properties. The dielectric response has been correlated with the BCT/BZT content displaying a maximum depending on the phase content. Additionally, in situ temperature-dependent Raman, permittivity, and pair distribution function (PDF) studies were performed from −60 °C to 130 °C to highlight the structure and phase evolution. In particular, the in situ temperature-dependent Raman measurements reveal sudden discontinuities in the vibrational modes that correspond to the structural changes in the perovskite structure. Therefore, the results of the permittivity response, based on the average of a large volume, are consistent with the local structural changes obtained by other techniques. Indeed, correlations of Raman, X-ray diffraction, and PDFs obtained from synchrotron X-ray total scattering data, along with permittivity measurements allowed the identification of the discrete ferro- to paraelectric phase transitions and a more robust characterization. The rotation and distortion of the octahedral caused by oxygen displacement are driving forces behind symmetry changes and phase transitions, explaining the mechanism of polymorphic phase transition based on A- and B-site substitution. Therefore, this work provides a comprehensive understanding of temperature and composition-dependent phase transitions in BCZ

The role of particle interactions on suspension rheology - Application to submicron grinding in stirred ball mills - Stenger, Frank; Peukert, Wolfgang (Chemical Engineering & Technology, 2003)
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.therol

The significance of the second osmotic virial coefficients for protein crystallization Die Bedeutung des zweiten osmotischen Virialkoeffizienten für die Proteinkristallisation - Wanka, Johanna; Peukert, Wolfgang (Chemie Ingenieur Technik, 2006)
Die Kristallisation der Proteine bietet eine gute und quantitative Möglichkeit zu ihrer Ab- trennung und Aufreinigung. Wichtigster und zeitaufwändigster Schritt der Kristallisation ist das Auffinden geeigneter Kristallisationsbedingungen meist über ein groß angelegtes Screening. Als prädiktiver Parameter für die Proteinkristallisation zur Reduzierung der not- wendigen Experimente wurde der zweite osmotische Virialkoeffizient B22 erkannt. Der Zu- sammenhang zwischen B22 und den Präzipitateigenschaften wurde bisher nur qualitativ hergestellt, es ist deshalb Thema dieser Untersuchungen, ihn zu quantifizieren.<br
Keywords: Kristallisation; Proteine; Prozessoptimierung

The Stokes–Einstein–Sutherland Equation at the Nanoscale Revisited - Baer, Andreas; Wawra, Simon; Bielmeier, Kristina; Uttinger, Maximilian; Smith, David M.; Peukert, Wolfgang; Walter, Johannes; Smith, Alexander Kingsbury (Small, 2023)
The Stokes–Einstein–Sutherland (SES) equation is at the foundation of statistical physics, relating a particle's diffusion coefficient and size with the fluid viscosity, temperature, and the boundary condition for the particle-solvent interface. It is assumed that it relies on the separation of scales between the particle and the solvent, hence it is expected to break down for diffusive transport on the molecular scale. This assumption is however challenged by a number of experimental studies showing a remarkably small, if any, violation, while simulations systematically report the opposite. To understand these discrepancies, analytical ultracentrifugation experiments are combined with molecular simulations, both performed at unprecedented accuracies, to study the transport of buckminsterfullerene C60 in toluene at infinite dilution. This system is demonstrated to clearly violate the conditions of slow momentum relaxation. Yet, through a linear response to a constant force, the SES equation can be recovered in the long time limit with no more than 4% uncertainty both in experiments and in simulations. This nonetheless requires partial slip on the particle interface, extracted consistently from all the data. These results, thus, resolve a long-standing discussion on the validity and limits of the SES equation at the molecular scale.
CRIS-Team Scopus Importer:2023-10-20
Keywords: analytical ultracentrifugation; boundary condition; Green–Kubo formalism; molecular dynamics; Stokes–Einstein–Sutherland equation

The synthesis of luminescent adenosine triphosphate passivated cadmium sulfide nanoparticles - Klupp Taylor, Robin; et al. (Journal of Materials Chemistry, 2003)

The synthesis of silica nanospheres doped with polyoxometalates - Klupp Taylor, Robin; et al. (Journal of the American Chemical Society, 2005)

Thin water films and magnesium hydroxide fiber growth - Gheisi, Amirreza; Sternig, Andreas; Redhammer, Guenther J.; Diwald, Oliver (RSC Advances, 2015)
Thin films of water covering highly dispersed metal oxides can give rise to the spontaneous and spatially controllable growth of hydroxide fibers in ambient air. Knowledge about the underlying formation mechanisms is key to the rational development of metal oxide nanomaterials and associated microstructures. We used SiCl4 as a water free chlorine ion source for the surface functionalization of MgO nanocubes and explored their subsequent transformation into magnesium oxychloride Mg3(OH)5Cl·4H2O fibers upon contact with water vapor. Specifically we show how the temperature of the functionalization process and material dispersion control the reaction pathway that can lead to very different products like Mg(OH)2, MgCl2·6H2O, or Mg3(OH)5Cl·4H2O and delineate a reaction mechanism. Lessons to be learned from this unique route to form hydroxide fibers under ambient conditions can be applied to a variety of microstructural evolution processes that involve metastable solids and superficial water acting both as a reactant and as a reaction medium for the hydration of metal oxide particle

Thin water films and particle morphology evolution in nanocrystalline MgO - Thomele, Daniel; Gheisi, Amirreza; Niedermaier, Matthias; Elsaesser, Michael S.; Bernardi, Johannes; Gronbeck, Henrik; Diwald, Oliver (Journal of the American Ceramic Society, 2018)
A key question in the field of ceramics and catalysis is how and to what extent residual water in the reactive environment of a metal oxide particle powder affects particle coarsening and morphology. With X‐ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), we investigated annealing‐induced morphology changes on powders of MgO nanocubes in different gaseous H2O environments. The use of such a model system for particle powders enabled us to describe how adsorbed water that originates from short exposure to air determines the evolution of MgO grain size, morphology, and microstructure. While cubic nanoparticles with a predominant abundance of (100) surface planes retain their shape after annealing to T = 1173 K under continuous pumping with a base pressure of water p(H2O) = 10−5 mbar, higher water partial pressures promote mass transport on the surfaces and across interfaces of such particle systems. This leads to substantial growth and intergrowth of particles and simultaneously favors the formation of step edges and shallow protrusions on terraces. The mass transfer is promoted by thin films of water providing a two‐dimensional solvent for Mg2+ ion hydration. In addition, we obtained direct evidence for hydroxylation‐induced stabilization of (110) faces and step edges of the grain surface
Keywords: interfaces; magnesium oxide; coarsening; grain growth

Three-dimensional and quantitative reconstruction of non-accessible internal porosity in hematite nanoreactors using 360 degrees electron tomography - Distaso, Monica; Apeleo Zubiri, Benjamin; Mohtasebi, Amirmasoud; Inayat, Alexandra; Dudak, Michal; Koci, Petr; Butz, Benjamin; Klupp Taylor, Robin; Schwieger, Wilhelm; Spiecker, Erdmann; Peukert, Wolfgang (Microporous and Mesoporous Materials, 2017)
In the current paper, mesocrystals are used as effective precursors to design nanoreactors with different kinds of enclosed porosity. The thermal treatment of hematite mesocrystalline nanoparticles is investigated as a post-processing tool for the engineering of internal organization of hierarchical structures. The porosity of starting materials and of particles thermally treated at different temperatures is investigated by transmission electron microscopy, nitrogen sorption and 360 degrees electron tomography. Virtual Capillary Condensation and Maximum Sphere Inscription are used as independent approaches for the quantitative assessment of internal porosity. The combination of experimental evidences and simulations provides a deep understanding of the internal topology of nanoreactors upon thermal treatment of mesocrystalline particles. This new design strategy may pave the way for exploring the use of the post treated mesocrystals as carriers to encapsulate materials for optoelectronic applications. (C) 2017 Elsevier Inc. All rights reserve
Keywords: Mesocrystals; Inorganic hollow nanoparticles; Compartmentalization; Encapsulation

Three-Dimensional Electrochemical Axial Lithography on Si Micro- and Nanowire Arrays - Rey, Marcel; Wendisch, Jan Fedja; Vogel, Nicolas; Diwald, Oliver; Bourret, Gilles Remi; Saller, Michael; Eadie, Alex; Reyer, Andreas; Musso, Maurizio (Nano Letters, 2018)
A templated electrochemical technique for patterning macroscopic arrays of single-crystalline Si micro- and nanowires with feature dimensions down to 5 nm is reported. This technique, termed three-dimensional electrochemical axial lithography (3DEAL), allows the design and parallel fabrication of hybrid silicon nanowire arrays decorated with complex metal nano-ring architectures in a flexible and modular approach. While conventional templated approaches are based on the direct replication of a template, our method can be used to perform high-resolution lithography on pre-existing nanostructures. This is made possible by the synthesis of a porous template with tunable dimensions that guides the deposition of well-defined metallic shells around the Si wires. The synthesis of a variety of ring architectures composed of different metals (Au, Ag, Fe, and Ni) with controlled sequence, height, and position along the wire is demonstrated for both straight and kinked wires. We observe a strong enhancement of the Raman signal for arrays of Si nanowires decorated with multiple gold rings due to the plasmonic hot spots created in these tailored architectures. The uniformity of the fabrication method is evidenced by a homogeneous increase in the Raman signal throughout the macroscopic sample. This demonstrates the reliability of the method for engineering plasmonic fields in three dimensions within Si wire array
Keywords: lithography; nano-rings; surface-enhanced Raman spectroscopy; plasmonics; Si nanowires

Three-dimensional simulation of viscous-flow agglomerate sintering - Peukert, Wolfgang; Kirchhof, Martin; Schmid, Hans-Joachim (Physical Review E, 2009)
The viscous-flow sintering of different agglomerate particle morphologies is studied by three-dimensional computer simulations based on the concept of fractional volume of fluid. For a fundamental understanding of particle sintering characteristics, the neck growth kinetics in agglomerate chains and in doublets consisting of differently sized primary particles is investigated. Results show that different sintering contacts in agglomerates even during the first stages are not completely independent from each other, even though differences are small. The neck growth kinetics of differently sized primary particles is determined by the smaller one up to a size difference by a factor of approximately 2, whereas for larger size differences, the kinetics becomes faster. In particular, the agglomerate sintering kinetics is investigated for particle chains of different lengths and for different particle morphologies each having ten primary particles and nine initial sintering contacts. For agglomerate chains, the kinetics approximately can be normalized by using the radius of the fully coalesced sphere. In general, different agglomerate morphologies show equal kinetics during the first sintering stages, whereas during advanced stages, compact morphologies show significantly faster sintering progress than more open morphologies. Hence, the overall kinetics cannot be described by simply using constant morphology correction factors such as fractal dimension or mean coordination number which are used in common sintering models. However, for the first stages of viscous-flow agglomerate sintering, which are the most important for many particle processes, a sintering equation is presented. Although we use agglomerates consisting of spherical primary particles, our methodology can be applied to other aggregate geometries as well. © 2009 The American Physical Society.
Keywords: sintering; agglomerate; simulation; kinetic; model

Tissue engineering of electrically responsive tissues using polyaniline based polymers: A review - Qazi, Taimoor Hasan; Rai, Ranjana; Boccaccini, Aldo R. (Biomaterials, 2014)
Conducting polymers have found numerous applications as biomaterial components serving to effectively deliver electrical signals from an external source to the seeded cells. Several cell types including cardiomyocytes, neurons, and osteoblasts respond to electrical signals by improving their functional outcomes. Although a wide variety of conducting polymers are available, polyaniline (PANI) has emerged as a popular choice due to its attractive properties such as ease of synthesis, tunable conductivity, environmental stability, and biocompatibility. PANI in its pure form has exhibited biocompatibility both invitro and invivo, and has been combined with a host of biodegradable polymers to form composites having a range of mechanical, electrical, and surface properties. Moreover, recent studies in literature report on the functionalization of polyaniline oligomers with end segments that make it biodegradable and improve its biocompatibility, two properties which make these materials highly desirable for applications in tissue engineering. This review will discuss the features and properties of PANI based composites that make them effective biomaterials, and it provides a comprehensive summary of studies where the use of PANI as a biomaterial component has enhanced cellular function and behavior. We also discuss recent studies utilizing functionalized PANI oligomers, and conclude that electroactive PANI and its derivatives show great promise in eliciting favorable responses from various cell lines that respond to electrical stimuli, and are therefore effective biomaterials for the engineering of electrically responsive biological tissues and organs. © 2014 Elsevier Ltd.
Keywords: Conducting polymers; Electrical stimulation; Polyaniline; Polyaniline oligomers; Tissue engineering

Top-down processing of submicron 45S5 Bioglass® for enhanced in vitro bioactivity and biocompatibility - Romeis, Stefan; Hoppe, Alexander; Detsch, Rainer; Boccaccini, Aldo R.; Schmidt, Jochen; Peukert, Wolfgang (Procedia Engineering, 2015)
45S5 Bioglass® (45S5BG - 45 wt.% SiO, 24.5 wt.% CaO, 24.5 wt.% NaO and 6 wt.% PO glass forming system) is a frequently applied type A bioactive material, forming an inherent bond to bone and soft tissue. Recent studies for nanometer sized bioactive glasses (nBG) have indicated their great potential for several biomedical applications. It is recognized that cost-efficient processing routes are required for the development of submicron bioactive glasses, given the advantages associated with the nanoscale. In this study, the potential of top-down processing of 45S5BG by wet comminution in a stirred media mill is investigated and the key importance of the used solvents is revealed: whereas bioactive submicron particles can be produced in organic solvents, as shown exemplarily for n-pentanol, bioactivity is lost after processing in water. Analysis of the elemental constituents in the solid phase by ICP-OES indicates enhanced dissolution during processing in water, i.e. The glass composition is changing during processing. In n-pentanol the overall composition and structure is maintained and only the formation of surface carbonates is observed; flake-like particles are obtained. As a marker for bioactivity in vitro hydroxycarbonate apatite formation as determined by FTIR is used; biocompatibility is addressed by in vitro incubation with osteoblast like MG-63 cells. All-together, we propose wet comminution under controlled conditions as an appropriate technique to produce submicrometer bioactive glass particles with enhanced bioactivit
Keywords: in vitro bioactivity and biocompatibility; solvent influence; submicron 45S5 Bioglass®; top-down

Top-down processing of submicron 45S5 Bioglass (R) for enhanced in vitro bioactivity and biocompatibility - Romeis, Stefan; Hoppe, Alexander; Detsch, Rainer; Boccaccini, Aldo R.; Schmidt, Jochen; Peukert, Wolfgang (2015)
45S5 Bioglass (R) (45S5BG - 45 wt.% SiO2, 24.5 wt.% CaO, 24.5 wt.% Na2O and 6 wt.% P2O5 glass forming system) is a frequently applied type A bioactive material, forming an inherent bond to bone and soft tissue. Recent studies for nanometer sized bioactive glasses (nBG) have indicated their great potential for several biomedical applications. It is recognized that cost-efficient processing routes are required for the development of submicron bioactive glasses, given the advantages associated with the nanoscale. In this study, the potential of top-down processing of 45S5BG by wet comminution in a stirred media mill is investigated and the key importance of the used solvents is revealed: whereas bioactive submicron particles can be produced in organic solvents, as shown exemplarily for n-pentanol, bioactivity is lost after processing in water. Analysis of the elemental constituents in the solid phase by ICP-OES indicates enhanced dissolution during processing in water, i.e. the glass composition is changing during processing. In n-pentanol the overall composition and structure is maintained and only the formation of surface carbonates is observed; flake-like particles are obtained. As a marker for bioactivity in vitro hydroxycarbonate apatite formation as determined by FTIR is used; biocompatibility is addressed by in vitro incubation with osteoblast like MG-63 cells. All-together, we propose wet comminution under controlled conditions as an appropriate technique to produce submicrometer bioactive glass particles with enhanced bioactivity. (C) 2015 The Authors. Published by Elsevier Ltd.
Keywords: submicron 45S5 Bioglass (R); top-down; solvent influence; in vitro bioactivity and biocompatibility

Topology-dependent light transport in planar plasmonic-photonic architectures - Tuzakli, Refik; Vogel, Nicolas; Romanova, Alexandra; Romanov, Sergei G.; Peschel, Ulf (European Conference on Lasers and Electro-Optics, CLEO 2015, 2014)

Towards a generally applicable methodology for the characterization of particle properties relevant to processing in powder bed fusion of polymers – from single particle to bulk solid behavior - Hesse, Nicolas; Winzer, Bettina; Peukert, Wolfgang; Schmidt, Jochen (Additive Manufacturing, 2021)
The majority of additively manufactured plastic parts built with powder bed fusion (PBF) processes are made of polyamide 12. Since only a fraction of powder ends up in the components built, part cake material and overflow powder has to be re-used for economic and ecologic reasons, even though its material properties are altered by thermo-mechanical stress during processing. Changes in bulk solid properties play a key role for the stability of the PBF process and the quality of manufactured parts. However, there is still no generally accepted method for the evaluation of used powders with respect to their processability and a lack of understanding of underlying bulk material mechanics. The aim of this study, exemplified for polyamide 12, is to assess widely applicable, standardized and process-adapted characterization methods in additive manufacturing and to shed light on the underlying phenomena causing the changes in flowability and packing properties of used powders.<br
Keywords: Powder bed fusion; Powder characterization; Powder flowability; Powder aging; Polyamide 12

Towards recombinantly produced milk proteins: Physicochemical and emulsifying properties of engineered whey protein beta-lactoglobulin variants - Keppler, Julia K.; Heyse, Anja; Scheidler, Eva; Uttinger, Maximilian; Fitzner, Laura; Jandt, Uwe; Heyn, Timon R.; Lautenbach, Vanessa; Loch, Joanna I.; Lohr, Jonas; Kieserling, Helena; Günther, Gabriele; et al. (Food Hydrocolloids, 2021)
CRIS-Team Scopus Importer:2020-08-07

Transfer of fracture mechanical concepts to bulk solids attrition in pneumatic conveying - Peukert, Wolfgang; Frye, Lars (International Journal of Mineral Processing, 2004)
In the present project, attrition in pneumatic conveying—as in <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/fracture-mechanics" title="Learn more about Fracture Mechanics from ScienceDirect's AI-generated Topic Pages">fracture mechanics and comminution—is regarded as a result of a process function (stress conditions) and a material function (influence of material properties). The first part of the paper describes the results of the determination of the stress conditions, where special emphasis is put on the numerical simulation of dilute-phase conveying. In the second part, results of single-particle tests are discussed. They simulate the two basic stress modes: impact and friction. The results show that the attrition behavior of the polymers tested changes between both stress modes. It is currently evaluated which material properties are suitable to describe this experimentally observed behavio
Keywords: Fracture mechanics: Computational fluid dynamics; Solid degradation; Pneumatic transport

Transfer of Individual Micro- and Nanoparticles for High-Precision 3D Analysis Using 360° Electron Tomography - Przybilla, Thomas; Apeleo Zubiri, Benjamin; Maria Beltran, Ana; Butz, Benjamin; Machoke, Albert; Inayat, Alexandra; Distaso, Monica; Peukert, Wolfgang; Schwieger, Wilhelm; Spiecker, Erdmann (Small Methods, 2017)
A versatile approach is demonstrated, providing a general routine for an extensive and advanced 3D characterization of individually selected micro- and nanoparticles, enabling the combination of complementary and scale-bridging techniques. Quintessential to the method is the transfer of individual particles onto tailored tips using a conventional scanning electron microscope equipped with a suitable micromanipulator. The method enables a damage- and contamination-free preparation of freestanding particles. This is of significant importance for applications addressing the measurement of structural, physical, and chemical properties of specifically selected particles, such as 360° electron tomography, atom probe tomography, nano X-ray tomography, or optical near-field measurements. In this context, the method is demonstrated for 360° electron tomography of micro-/macroporous zeolite particles with sizes in the micrometer range and mesoporous alpha-hematite nanoparticles exhibiting sizes of 50–100 nm, including detailed pre- and post-characterization on the nanoscal
Keywords: 360 degrees electron tomography; dual-beam SEM/FIB; micromanipulation; pick and place; sample preparation

Translational and Rotational Diffusion Coefficients of Gold Nanorods Dispersed in Mixtures of Water and Glycerol by Polarized Dynamic Light Scattering - Bioucas, Francisco; Damm, Cornelia; Peukert, Wolfgang; Rausch, Michael Heinrich; Koller, Thomas Manfred; Giraudet, Cédric; Fröba, Andreas Paul (Journal of Physical Chemistry B, 2019)
Polarized dynamic light scattering (DLS) gives access to orientation-averaged translational and rotational diffusion coefficients of anisotropic particles dispersed in fluids in a single experiment. As the combination of both diffusivities contains information on the morphology of the particles, their simultaneous and accurate measurement for the same sample and thermodynamic state is beneficial for particle characterization. For nontransparent model suspensions of gold nanorods in water and water-glycerol mixtures, a scattering geometry in reflection direction was realized, which minimizes multiple scattering and allows using low laser powers to avoid laser heating. Furthermore, a heterodyne detection scheme was guaranteed by superimposing much stronger reference light to the scattered light. This ensures an unambiguous data evaluation and reduces the uncertainties for the rotational and the translational diffusivity, where the latter is accessible with smaller uncertainty. For the water-based suspensions, both diffusivities agree well with the stick hydrodynamic theory for rods and show an Andrade-type behavior in the studied temperature range from 271 to 323 K. The measured results for both diffusivities, particularly for the rotational diffusivity, indicate a breakdown of the stick boundary conditions for dynamic viscosities larger than 4 mPa·s.
CRIS-Team Scopus Importer:2019-11-08

Transmission electron microscopy and time resolved optical spectroscopy study of the electronic and structural interactions of ZnO nanorods with bovine serum albumin - Klaumünzer, Martin; Weichsel, Ulrike; Mackovic, Mirza; Spiecker, Erdmann; Peukert, Wolfgang; Kryschi, Carola; Spiecker, Erdmann; Mackovic, Mirza (Journal of Physical Chemistry B, 2013)
The adsorption behavior and electronic interactions of bovine serum albumin (BSA) with ZnO nanorod surfaces were investigated using high-resolution transmission electron microscopy as well as stationary and time-resolved optical spectroscopy techniques. Transmission electron microscopy shows that ZnO nanorod surfaces are surrounded by a homogeneous amorphous BSA film with thicknesses between ∼2.5 and 5.0 nm. The electronic structure and adsorption geometry of BSA were examined using high-angle annular dark field scanning transmission electron microscopy combined with electron energy loss spectroscopy. The adsorption process was observed to result into an unfolded conformation of BSA becoming predominantly bound in the side-on orientation at the ZnO surface. This adsorption mode of the BSA molecules allows for a strong interaction with surface states of the ZnO nanorods. This is obvious from its efficient quenching of the defect-center photoluminescence of ZnO. Complementary information of electronic interactions across the ZnO nanorod interface was obtained from femtosecond transient absorption spectroscopy experiments. The rise dynamics of the measured transients revealed altered hole trapping dynamics and, thus, indicated to heterogeneous charge transfer as emerging from adsorbed BSA molecules to defect centers of the ZnO interface. © 2013 American Chemical Society.

Transparency and damage tolerance of patternable omniphobic lubricated surfaces based on inverse colloidal monolayers - Vogel, Nicolas; et al. (Nature Communications, 2013)

Transparent antifouling material for improved operative field visibility in endoscopy - Sunny, Steffi; Cheng, George; Daniel, Daniel; Lo, Peter; Ochoa, Sebastian; Howell, Caitlin; Vogel, Nicolas; Majid, Adnan; Aizenberg, Joanna (Proceedings of the National Academy of Sciences of the United States of America, 2016)
Camera-guided instruments, such as endoscopes, have become an essential component of contemporary medicine. The 15-20 million endoscopies performed every year in the United States alone demonstrate the tremendous impact of this technology. However, doctors heavily rely on the visual feedback provided by the endoscope camera, which is routinely compromised when body fluids and fogging occlude the lens, requiring lengthy cleaning procedures that include irrigation, tissue rubbing, suction, and even temporary removal of the endoscope for external cleaning. Bronchoscopies are especially affected because they are performed on delicate tissue, in high-humidity environments with exposure to extremely adhesive biological fluids such as mucus and blood. Here, we present a repellent, liquid-infused coating on an endoscope lens capable of preventing vision loss after repeated submersions in blood and mucus. The material properties of the coating, including conformability, mechanical adhesion, transparency, oil type, and biocompatibility, were optimized in comprehensive in vitro and ex vivo studies. Extensive bronchoscopy procedures performed in vivo on porcine lungs showed significantly reduced fouling, resulting in either unnecessary or 10-15 times shorter and less intensive lens clearing procedures compared with an untreated endoscope. We believe that the material developed in this study opens up opportunities in the design of next-generation endoscopes that will improve visual field, display unprecedented antibacterial and antifouling properties, reduce the duration of the procedure, and enable visualization of currently unreachable parts of the body, thus offering enormous potential for disease diagnosis and treatment.
Keywords: Antifouling materials; Biopsy; Endoscopy; Surface wetting

Treatment of polymer powders by combining an atmospheric plasma jet and a fluidized bed reactor - Sachs, Marius; Schmidt, Jochen; Peukert, Wolfgang; Wirth, Karl-Ernst (Powder Technology, 2018)
Keywords: Atmospheric pressure plasma; Fluidized bed reactor; Additive manufacturing; Polymers; Secondary gas injection

Tunable Anisotropy in Inverse Opals and Emerging Optical Properties - Vogel, Nicolas; et al. (Chemistry of Materials, 2014)
Using self-assembly, nanoscale materials can be fabricated from the bottom up. Opals and inverse opals are examples of self-assembled nanomaterials made from crystallizing colloidal particles. As self-assembly requires a high level of control, it is challenging to use building blocks with anisotropic geometry to form complex opals, which limits the possible structures. Typically, spherical colloids are employed as building blocks, leading to symmetric, isotropic superstructures. However, a significantly richer palette of directionally dependent properties are expected if less symmetric, anisotropic structures can be created, especially originating from the assembly of regular, spherical particles. Here we show a simple method for introducing anisotropy into inverse opals by subjecting them to a post-assembly thermal treatment that results in directional shrinkage of the silica matrix caused by condensation of partially hydrated sol gel silica structures. In this way, we can tailor the shape of the pores, and the anisotropy of the final inverse opal preserves the order and uniformity of the self-assembled structure. Further, we prevent the need to synthesize complex oval-shaped particles and crystallize them into such target geometries. Detailed X-ray photoelectron spectroscopy and infrared spectroscopy studies clearly identify increasing degrees of sol-gel condensation in confinement as a mechanism for the structure change. A computer simulation of structure changes resulting from the condensation-induced shrinkage further confirmed this mechanism. As an example of property changes induced by the introduction of anisotropy, we characterized the optical spectra of the anisotropic inverse opals and found that the optical properties can be controlled in a precise way using calcination temperature.

Tunable conduction type of solution-processed germanium nanoparticle based field effect transistors and their inverter integration - Peukert, Wolfgang; Meric, Zeynep; Mehringer, Christian; Jank, Michael; Frey, Lothar; Karpstein, Nicolas (Physical Chemistry Chemical Physics, 2015)
In this work we demonstrate the fabrication of germanium nanoparticle (NP) based electronics. The whole process chain from the nanoparticle production up to the point of inverter integration is covered. Ge NPs with a mean diameter of 33 nm and a geometric standard deviation of 1.19 are synthesized in the gas phase by thermal decomposition of GeH4 precursor in a seeded growth process. Dispersions of these particles in ethanol are employed to fabricate thin particulate films (60 to 120 nm in thickness) on substrates with a pre-patterned interdigitated aluminum electrode structure. The effect of temperature treatment, polymethyl methacrylate encapsulation and alumina coating by plasma-assisted atomic layer deposition (employing various temperatures) on the performance of these layers as thin film transistors (TFTs) is investigated. This coating combined with thermal annealing delivers ambipolar TFTs which show an Ion/Ioff ratio in the range of 102. We report fabrication of n-type, p-type or ambipolar Ge NP TFTs at maximum temperatures of 450 °C. For the first time, a circuit using two ambipolar TFTs is demonstrated to function as a NOT gate with an inverter gain of up to 4 which can be operated at room temperature in ambient ai
Keywords: nanoparticle; electronic; thermal; decomposition; growth; particulate; film

Tuning photoluminescence properties of alkaline-earth oxide nanoparticles by site-selective functionalization and doping - Sushko, P. V.; McKenna, K. P.; Shluger, A. L.; Diwald, Oliver (ECS Transactions, Volume 25, Number 9, 2009)
We investigate theoretically the effects of isovalent substitutional doping on the optical properties of cubic MgO nanoparticles. The Ca, Sr, and Ba impurities preferentially occupy the three-coordinated cation sites and counterbalance the lattice strain induced by the finite size of the host particles. The lowest optical absorption band shifts to the lower energies as the radius of the substitutional species increases. Two types of nearly iso-energetic triplet excitons are found: the symmetric and asymmetric configurations correspond to the hole component being delocalized over three four-coordinated anion and localized on a single anion, respectively. The photoluminescence energies strongly depend on the exciton configuration and can be controlled by the judicious choice of the dopans

Tuning surface wettability of Al and its correlation with short and long term corrosion resistance in saline solutions - Khajavian, Ehsan; Attar, Mohammad Reza; Mohammadi-Zahrani, Ehsan; Liu, Wei; Davoodi, Ali; Hosseinpour, Saman (Surface & Coatings Technology, 2021)
In this work, we fabricated superhydrophilic aluminum alloy (AA 6063) with a hierarchical labyrinth-like structure using a facile and environmentally benign chemical etching method. The patterned samples were functionalized by stearic acid molecules to obtain superhydrophobic samples with water contact angle (CA) >160°, at optimum conditions. Although the superhydrophobic samples initially exhibited up to two orders of magnitude better corrosion resistance compared to as-received samples, their corrosion performance and CA gradually reduced upon prolonged exposure to 3.5 wt% NaCl solution. Hence, the initial high CA in superhydrophobic surface layers cannot be used as a measure of their long-term corrosion stability.

Tuning the Molecular Order of C60 Functionalized Phosphonic Acid Monolayers - Rumpel, Armin; Novak, Michael; Walter, Johannes; Braunschweig, Björn; Halik, Marcus; Peukert, Wolfgang (Langmuir, 2011)
Mixed self-assembled monolayers (SAM) of alkyl phosphonic acids and C60 functionalized octadecyl phosphonic acids (C60C18–PA) are deposited on alumina substrates from solution and are shown to form wellordered structures with an insulating layer of alkyl chains and a semiconducting layer that comprises mainly C60. Such an ordered structure is a necessity for the application of SAMs in organic transistors but is difficult to obtain since C60C18–PA without additional support do self-assemble in dense packaging but not in a well-ordered fashion. To avoid disordering of the SAM and to gain a better control of the interfacial properties we have investigated the stabilizing effects of fluorinated dodecyl phosphonic acids (FC12–PA) on the C60C18–PA monolayer. Vibrational sum-frequency (SFG) spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and electrical measurements were applied to study the mixed monolayers. Here, we make use of the differently labeled PA to determine surface coverages and molecular properties of the two species independently. Adsorption of FC12–PA gives rise to vibrational bands at 1344 cm-1 and 1376 cm-1 in SFG spectra, while a pronounced vibrational band centered at 1465 cm-1 is attributable to C60 vibrations. The coexistence of the bands is indicative for the presence of a mixed monolayer that is composed of both molecular species. Furthermore, a pronounced maximum in SFG intensity of the C60 band is observed for SAMs, which are deposited from solutions with  75% C60C18–PA and  25% FC12–PA. The intensity maximum originates from successful stabilization of C60 modified C60C18–PA by FC12–PA and a significantly improved molecular order. Conclusions from SFG spectra are corroborated by electric measurements that show best performance at these concentrations. Our results provide new information on the morphology and composition of C60 modified SAMs and establish a route to fabricate well-defined layers for molecular scale organic electronics.
Keywords: Thickness; Nonlinear optics; Layers; Monolayers

Tuning the molecular order of C-60 functionalized phosphonic acids - Rumpel, Armin; Novak, Michael; Walter, Johannes; Braunschweig, Björn; Halik, Marcus; Peukert, Wolfgang (2012)

Tuning the Properties of CZTS Films by Controlling the Process Parameters in Cost-Effective Non-vacuum Technique - Abdelhaleem, Soraya; Hassanien, A.E.; Ahmad, Rameez; Schuster, Matthias; Ashour, A.H.; Distaso, Monica; Peukert, Wolfgang; Wellmann, Peter (Journal of Electronic Materials, 2018)
Highly dispersive Cu2ZnSnS4 (CZTS) nanoparticles were successfully synthesized by a simple solvothermal route. A low cost, non-vacuum method was used to deposit CZTS nanoparticle ink on glass substrates by a doctor blade process followed by selenization in a tube furnace to form Cu2ZnSn (S,Se)4 (CZTSSe) layers. Different selenization conditions and particle concentrations were considered in order to improve the crystallinity and surface morphology; the annealing temperature was varied between 400C and 550C and the annealing time was varied between 5 min and 20 min in a seleniumnitrogen atmosphere. The influence of annealing conditions on structural, compositional, optical and electrical properties of CZTSSe thin films was studied. An improvement in the structural and surface morphology was observed with increasing of annealing temperature (up to 500C). An enhancement in the crystallinity and surface morphology were observed for thin films annealed for 10–15 min. Absorption study revealed that the band gap energy of as-deposited CZTS thin film was approximately 1.43 eV, while for CZTSSe thin films it ranged from 1.15 eV to 1.34 eV at different annealing temperatures, and from 1.33 eV to 1.38 eV for different annealing times.<br
Keywords: CZTSSe; selenization; solvothermal; thin films; doctor blade; resistivity

Tuning the size and the optical properties of ZnO mesocrystals synthesized under solvothermal conditions - Distaso, Monica; Segets, Doris; Wernet, Ruth; Peukert, Wolfgang; Klupp Taylor, Robin (Nanoscale, 2012)
Mesocrystals are a promising class of nanomaterials enabling new optical and mechanical properties due to their three dimensional organization of primary crystallites sharing a common crystallographic orientation. In the present article, the influence of process parameters such as temperature profile and stirring on the primary and secondary size of ZnO mesocrystals synthesized under solvothermal conditions has been investigated. In general, small but noticeable lattice strain is introduced to the particles during the synthesis process. Additionally, with increasing mass transport the fusion of primary crystallites due to coarsening is enhanced. A closer analysis revealed an influence of the polymer chain length on the final particle structure throughout different hierarchical levels. Based on our findings a reaction mechanism with nucleation and growth taking place embedded in poly-N-vinylpyrrolidone (PVP), followed by a polymer-mediated step of oriented aggregation and subsequent coarsening is proposed. In consequence, the careful control throughout all hierarchical levels of particle synthesis allows fine-tuning of the optical properties of ZnO mesocrystals which show a high UV absorption and minimal scattering in the visible region. © 2012 The Royal Society of Chemistry.

Ultrafast excitation energy transfer in vinylpyridine terminated silicon quantum dots - Sommer, Anja; Cimpean, Carla Ramona; Kunz, Michael; Oelsner, Christian; Kupka, Hans J.; Kryschi, Carola (Journal of Physical Chemistry C, 2011)
Water-soluble 2- and 4-vinylpyridine terminated silicon quantum dots (SiQDs) with sizes between 2 and 3 nm were obtained by HF etching of oxidized SiQDs and subsequently passivating with vinylpyridine ligands via thermal hydrosilylation. The functionalized SiQDs emit photoluminescence in the blue-green spectrum with quantum yields around 30%. The photoluminescence is ascribed to radiative recombination of excitons confined to the SiQD core. Indication of efficient electronic interactions between excited ligand states and SiQD conduction band states has been achieved by real-time monitoring excitation relaxation dynamics on the subpicosecond time scale using time-resolved laser spectroscopy techniques. The observed ultrafast excitation relaxation dynamics involving decay and rise dynamics faster than 1 ps were ascribed to electronic excitation energy transfer from an initially photoexcited ligand state to SiQD conduction band states. These results were analyzed by performing a state population analysis on the basis of electron exchange interactions. © 2011 American Chemical Society.

Ultrafast exciton relaxation dynamics in silicon quantum dots - Cimpean, Carla Ramona; Groenewegen, Vincent; Kuntermann, Volker; Sommer, Anja; Kryschi, Carola (Laser & Photonics Reviews, 2009)
The photoluminescence properties of silicon quantum dots may be tailored by surface states via efficient coupling to resonant bulk states. Therefore various wet-chemistry procedures were developed to fabricate silicon quantum dots with adjustable sizes and surface properties. While the energy gap of the Si core is tuned by the size, resonant electronic surface states may be attained by varying the structure and chemical composition of the grafting. The strength of electronic couplings between surface and bulk states determines the timescale of both photo-induced electron transfer from excited surface states to conduction band states and capture of conduction band electrons by surface states. Whereas the origin of photoluminescence and therewith the quantum dot size distribution may be elucidated by stationary luminescence spectroscopy, ultrafast optical spectroscopy techniques, for instance the femtosecond transient absorption spectroscopy, allow to monitor photo-induced electron transfer between surface and bulk states and carrier trapping on the subpicosecond timescale. © 2009 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Silicon quantum dots; photoluminescence; thermal hydrosilylation; femtosecond spectroscopy; photo-induced electron transfe

Ultrasensitive Ultraviolet Chiral Plasmonic Biosensor Based on Passivated Al Shells - Huang, Shanshan; Wang, Siyi; Yang, Xiu; Görlitzer, Eric; Peng, Jialong; Liu, Zhuang; Chikkaraddy, Rohit; Du, Jinglei; Vogel, Nicolas; Hou, Yidong (ACS Applied Materials and Interfaces, 2025)
Chiroptical spectroscopic techniques offer a nondestructive means of elucidating the stereochemical structures of biomolecules and have demonstrated significant applications across diverse fields, including bioscience, biomedicine, and clinical diagnosis, among others. However, the inherently weak chiroptical effects exhibited by natural chiral molecules pose a significant challenge to detection sensitivity. In this study, we demonstrate an ultrasensitive ultraviolet chiral plasmonic biosensor (CPB) that leverages a self-assembled metasurface composed of passivated aluminum chiral shells (ACSs). By meticulously optimizing the geometry and size of these shells, we achieve a uniform, large, and readily accessible superchiral field on the top surface of the ACSs, thereby enhancing their interaction with chiral biomolecules. In addition, the abundant surface lattice resonance (SLR) modes excited in the ultraviolet waveband narrow the chiroptical resonance peaks and improve the identifiability of sensor pointers. In experiments, large-area ACSs with strong chiroptical effects were realized by depositing Al on a colloidal monolayer with hexagonal order and then passivating it with ozone to improve stability. When immersed in solutions containing chiral molecules, the g-factor maxima of the ACSs exhibit a notable peak shift that correlates with both the stereochemical structures and the concentrations of the biomolecules. Notably, the consistency chiral sensor parameter U reaches 10.9095 for the null point and 0.1739 for peaks of g-factor spectra, which makes a record in the field CPBs. The systematic analysis of the SLR modes, superchiral field, and chiral sensor parameters further rationalizes the record chiral sensor performance realized in this work.
CRIS-Team Scopus Importer:2025-05-09
Keywords: chiral biosensor; chiral field; chiroptical effect; glancing angle deposition; microsphere lithography; ultraviolet chiral metamaterials

Unified Design Strategies for Particulate Products - Peukert, Wolfgang; Segets, Doris; Pflug, Lukas; Leugering, Günter (Academic Press Inc., 2015)
Unit operations and product design are the two most important pillars of chemical engineering. Product design is the formation, formulation, handling, manufacturing, and characterization of complex multiphase products with specific properties and is thus at the core of mesoscale science and engineering. The applications define the required product properties which cover both classical fields of process technology in the chemical industry as well as new emerging fields of electronics, energy and environmental technologies, life sciences, materials science and engineering, nanotechnology, and photonic technologies highlighting the broad relevance of mesoscale science. Unifying principles of product design are proposed which are widely applicable to many different kinds of products including solid, liquid, and even gaseous particles. Results from the Erlangen Cluster of Excellence "Engineering of Advanced Materials" show that the joint venture of chemical engineering with materials science in concert with the basic sciences opens new prospects for all involved disciplines. In particular, chemical and biochemical engineering expands through particle technologies also in physics-related fields of technology such as electronics, photonics, or 3D printing. Rigorous mathematical optimization methods based on predictive models for products, structures, and processes catalyze new possibilities for true design of particulate products which is at the core of mesoscale science and technolog
Keywords: Bottom up; Hierarchical systems; Multiscale; Optimization; Product design; Structure formation; Top down; Unifying principles

Unraveling Complexity: A Strategy for the Characterization of Anisotropic Core Multishell Nanoparticles - Lin, Wei; Greve, Christoph; Härtner, Sebastian; Götz, Klaus; Walter, Johannes; Wu, Mingjian; Rechberger, Stefanie; Spiecker, Erdmann; Busch, Sebastian; Schmutzler, Tilo; Avadhut, Yamini; Hartmann, Martin; et al. (Particle & Particle Systems Characterization, 2020)
In this work, a widely applicable routine to characterize the core, surface, stability, and optical properties of CdSe/CdS/ZnS core–shell–shell nanorods after multiple growth steps is established. First, size, shape, and shell thickness of the nanorods are characterized by transmission electron microscopy (TEM), analytical ultracentrifugation (AUC), and small angle X-ray/neutron scattering (SAXS/SANS). In the next step, Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and SANS measurements are applied to determine the surface species of nanorods. Then, the colloidal stability of the nanorods is investigated by UV–vis spectroscopy and dynamic light scattering (DLS) after different washing cycles. Finally, photoluminescence quantum yield (PLQY) of the nanorods during washing and sample storage is determined. With this highly complementary routine for particle characterization, the core, surface, stability, and optical properties of nanorods after multiple growth steps are resolved. The results demonstrate the importance of the developed toolbox to characterize such highly complex, anisotropic nanorods for a technical environment. This is of major importance for the handling of colloidal quantum materials and their quality control in industrial applications.
CRIS-Team Scopus Importer:2020-09-11
Keywords: anisotropic; characterization; core multishell; nanoparticles

Untersuchungen zum Einfluß der Strömungsstruktur auf den wandseitigen Wärmeübergang in Downer-Reaktoren - Wirth, Karl-Ernst; Lehner, Peter (Chemie Ingenieur Technik, 1999)
Im Bereich der heterogen katalysierten Reaktionen nehmen Gas-Feststoff-Reaktionen eine wichtige  Stellung ein. Bei diesen Reaktionen  ist die  Umwandlung der Edukte in das gewünschte Zielprodukt oft von Folge- und Parallelreaktionen begleitet,  die zu einer reduzierten  Produktausbeute fihren. Mit einer im Hinblick auf den Reaktionsablauf optimierten Stromungsfuhrung im Reaktor kann man dem entgegenwirken und zur Erhohung der Produktausbeute entscheidend beitragen. So ist z. B. eine enge Verweilzeitverteilung bei vielen Reaktionen unerlaRlich, um die oben angesprochenen Nebenreaktionen zu minimieren. Diese Anforderung kann von den momentan eingesetzten GadFeststoff- Reaktoren, wie  z. B. den blasenbildenden Wirbelschichten oder  Riser-Reaktoren, meistens nicht  erfüllt werden. In der Fachwelt wird aus diesem Grund das Konzept des Downer-Reaktors  diskutiert, bei dem Gas und Feststoff gleichsinnig in Richtung der Erdschwere strömen. Bisher durchgeführte Untersuchungen haben sich auf den Einlaufbereich des Reaktors  konzentriert, da der Stromungszustand  und damit auch die Effizienz des Downers schon durch die Feststoffaufgabe entscheidend beeinflufit werden kann. Zur  verlaglichen  Auslegung eines chemischen Reaktors  sind aber  auch Informationen  über das Warmeübertragungsverhalten   notwendig.  Untersuchungen zum Warmeubergang im Aufstromteil von  zirkulierenden Wirbelschichten  zeigen, dass das  wandseitige  Warmeiibertragungsverhalten von der Feststoffkonzentration an der Rohrwand entscheidend beeinflusst wird. Es steht zu vermuten, dass die Verteilung der Feststoffkonzentration im Querschnitt des Downer-Reaktors fur den wandseitigen Warme- übergang von besonderer Bedeutung  ist.  Eine Untersuchung  des Warmeübergangsverhaltens von Downer-Reaktoren ist deshalb nur unter gleichzeitiger Betrachtung der Konzentrationsverteilung des Feststoffs  über  dem  Rohrquerschnitt sinnvoll.
UnivIS-Import:2015-03-05:Pub.1999.tech.ITC.mechve.unters_29
Keywords: wirbelschicht; pulver; partikel; strömung

Use of COSMO-RS for the prediction of adsorption equilibria - Peukert, Wolfgang; Mehler, Carsten; Klamt, Andreas (Aiche Journal, 2002)
The novel method COSMO-RS for the calculation of thermodynamic partition equilibria based on quantum chemical calculations is applied for the first time to the correlation and prediction of adsorption equilibria. In the limit of small adsorbate concentrations, very good predictions have been achieved for adsorption equilibria of activated carbon for both the phase and the aqueous phase.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.useofc
Keywords: thermodynamic; simulation; equilibrium

Using carbon nanodots as inexpensive and environmentally friendly sensitizers in mesoscopic solar cells - Margraf, Johannes; Lodermeyer, Fabian; Strauß, Volker; Haines, Philipp; Walter, Johannes; Peukert, Wolfgang; Costa, Ruben Dario; Clark, Timothy; Guldi, Dirk Michael (Nanoscale Horizons, 2016)
We discuss the use of carbon nanodots (CNDs) as sensitizers in mesoscopic solar cells. The CNDs are synthesized using a one-step, bottom-up microwave approach with citric acid, urea, and formic acid as precursors in aqueous media. Their light-harvesting capabilities can be tuned by adjusting the synthetic parameters. Comprehensive spectroscopic and theoretical studies allow us to rationalize the nature of their absorption features. Promising power conversion efficiencies ( extgreekh) of 0.24% can be achieved from these cheap and eco-friendly sensitizers by optimizing the solar-cell assembly process. Interestingly, we found that extending the light absorption towards longer wavelengths does not necessarily improve the performance of the solar cells, since the longer-wavelength absorption features hardly contribute to the cells' photo-action spectra, so that the overall power conversion efficiency is actually worse. The origin of the lower performance is corroborated in transient absorption spectroscopy and photovoltage decay measurements. Our work points, on one hand, to the limits of as-synthesized CNDs as photosensitizers and, on the other hand, to possible improvements.

Versatile strategy for homogeneous drying patterns of dispersed particles - Rey, Marcel; Walter, Johannes; Harrer, Johannes; Perez, Carmen Morcillo; Chiera, Salvatore; Nair, Sharanya Sukumar; Ickler, Maret; Fuchs, Alesa; Michaud, Mark; Uttinger, Maximilian; Schofield, Andrew B.; Thijssen, Job H. J.; et al. (Nature Communications, 2022)
After spilling coffee, a tell-tale stain is left by the drying droplet. This universal phenomenon, known as the coffee ring effect, is observed independent of the dispersed material. However, for many technological processes such as coating techniques and ink-jet printing a uniform particle deposition is required and the coffee ring effect is a major drawback. Here, we present a simple and versatile strategy to achieve homogeneous drying patterns using surface-modified particle dispersions. High-molecular weight surface-active polymers that physisorb onto the particle surfaces provide enhanced steric stabilization and prevent accumulation and pinning at the droplet edge. In addition, in the absence of free polymer in the dispersion, the surface modification strongly enhances the particle adsorption to the air/liquid interface, where they experience a thermal Marangoni backflow towards the apex of the drop, leading to uniform particle deposition after drying. The method is independent of particle shape and applicable to a variety of commercial pigment particles and different dispersion media, demonstrating the practicality of this work for everyday processes.
CRIS-Team WoS Importer:2022-06-10

Vibrational Spectroscopy in Studies of Atmospheric Corrosion - Hosseinpour, Saman; Johnson, Magnus (Materials, 2017)
Vibrational spectroscopy has been successfully used for decades in studies of the atmospheric corrosion processes, mainly to identify the nature of corrosion products but also to quantify their amounts. In this review article, a summary of the main achievements is presented with focus on how the techniques infrared spectroscopy, Raman spectroscopy, and vibrational sum frequency spectroscopy can be used in the field. Several different studies have been discussed where these instruments have been used to assess both the nature of corrosion products as well as the properties of corrosion inhibitors. Some of these techniques offer the valuable possibility to perform in-situ measurements in real time on ongoing corrosion processes, which allows the kinetics of formation of corrosion products to be studied, and also minimizes the risk of changing the surface properties which may occur during ex-situ experiments. Since corrosion processes often occur heterogeneously over a surface, it is of great importance to obtain a deeper knowledge about atmospheric corrosion phenomena on the nano scale, and this review also discusses novel vibrational microscopy techniques allowing spectra to be acquired with a spatial resolution of 20 nm.
Keywords: atmospheric corrosion; infrared spectroscopy; Raman spectroscopy; vibrational sum frequency spectroscopy; VSFS; SFG

Vibrational sum-frequency generation at protein modified air–water interfaces: Effects of molecular structure and surface charging - Engelhardt, Kathrin; Peukert, Wolfgang; Braunschweig, Björn (Current Opinion in Colloid & Interface Science, 2014)
Protein and surfactant modified air–water interfaces are an important model system for colloid science as many applications for example aqueous foams in food products rely on our knowledge and ability to tune molecular structures at these interfaces. That is because interfaces are a fundamental building block in the hierarchical structure of foam, where in fact the molecular level can determine properties on larger length scales. For that reason it is of great importance to increase our ability to study air–water interfaces with molecular level probes and to obtain not only information on coverage but also direct information on interfacial composition, molecular order, orientations as well as information on the charged state of an interface. Vibrational sum-frequency generation (SFG) is a powerful tool that can help to address these issues and is inherently surface sensitive. In this contribution we will review recent developments in the use of SFG for studies of biomolecules at aqueous interfaces and discuss current issues with the interpretation of SFG spectra from electrified interfaces. In order to guide interpretations from interface spectroscopy we invoke the use of complementary methods such as ellipsometry and zetapotential measurements of bulk molecules.
Keywords: Surfactants; Interface spectroscopy; Foam; Sum-frequency generation; Proteins

Wafer-Scale Fabrication of Ordered Binary Colloidal Monolayers with Adjustable Stoichiometries - Vogel, Nicolas; et al. (Advanced Functional Materials, 2011)
Colloidal monolayers with high order and increased complexity beyond plain hexagonal packing geometries are useful for 2D templating of surface nano-structures and lithographic applications. Here, binary colloidal monolayers featuring a close-packed monolayer of large spheres (L) with a superlattice of small particles (S) are prepared in a single step using a Langmuir trough. Adjustment of the stoichiometry of the two particle types at the air-water interface leads to a high degree of control over the occupation of the interstitial sites in the close-packed layer of large spheres by the small colloids. Thus, large areas of binary 2D crystals with LS 2, LS 6, and LS 9 structures are fabricated in a controlled way. The process allows the formation of binary crystals over a wide range of particle size ratios from 0.19 to 0.40. The pH value of the subphase can be used to enhance the crystallization process by changing the contact angle of the particles at the interface. An interfacial polymerization of butyl cyanoacrylate is used to directly image the contact angle of the colloids at the interface. Transfer to solid substrates is achieved by a surface lowering technique. A variety of substrates with arbitrary topographies can thus be decorated with colloidal monolayers. Applied to a lithographic process, such monolayer architectures allow the generation of complex patterns, not accessible with conventional close-packed monolayers.

Wall-to-Suspension Heat Transfer in Circulating Fluidized Beds - Wirth, Karl-Ernst (Preprints 13th International Conference on Fluidized Bed Combustion, 1995)
The wall-to-suspension heat transfer in circulating fluidized beds depends on the fluid mechanics immediately near the wall and on the thermal properties of the gas used. Experimental investigations of circulating fluidized beds of low dimensionless pressure gradients with different solid particles such as bronze, glass, and polystyrene at ambient temperatures showed no influence of the conductivity and the heat capacity of the solids on the heat transfer coefficient. Consequently the heat transfer coefficient in the form of the dimensionless Nusselt number can be described by the dimensionless numbers which characterize the gas-solid-flow near the wall. With the aid of a model of segregated vertical gas-solid flow, the flow pattern in the wall region can be calculated and thus the wall heat transfer which depends only on heat conduction in the gas and on the convective heat transfer by the gas. A simple correlation is presented for calculating the wall-to-suspension heat transfer in circulating fluidized beds.
UnivIS-Import:2015-04-16:Pub.1995.tech.ITC.mechve.wallto
Keywords: fluidization; bed; heat; transfer

Water Orientation at the Calcite-Water Interface - Söngen, Hagen; Schlegel, Simon J.; Jaques, Ygor Morais; Tracey, John; Hosseinpour, Saman; Hwang, Doyk; Bechstein, Ralf; Bonn, Mischa; Foster, Adam S.; Kühnle, Angelika; Backus, Ellen H.G. (Journal of Physical Chemistry Letters, 2021)
Mineral-water interfaces play an important role in many natural as well as technological fields. Fundamental properties of these interfaces are governed by the presence of the interfacial water and its specific structure at the surface. Calcite is particularly interesting as a dominant rock-forming mineral in the earth’s crust. Here, we combine atomic force microscopy, sum-frequency generation spectroscopy, and molecular dynamics simulations to determine the position and orientation of the water molecules in the hydration layers of the calcite surface with high resolution. While atomic force microscopy provides detailed information about the position of the water molecules at the interface, sum-frequency generation spectroscopy can deduce the orientation of the water molecules. Comparison of the calcite-water interface to the interfaces of magnesite-water, magnesite-ethanol, and calciteethanol reveals a comprehensive picture with opposite water orientations in the first and second layer of the interface, which is corroborated by the molecular dynamics simulation

Wear and tribological characterization of nickel matrix electrodeposited composites: A review - Sajjadnejad, Mohammad; Haghshenas, Seyyed Mohammad Saleh; Badr, Parnia; Setoudeh, Nader; Hosseinpour, Saman (Wear, 2021)
Electrodeposited metal matrix composite coatings (MMCs) often exhibit superior surface characteristics including corrosion resistance in a wide range of temperatures, improved physical, mechanical, and tribological properties, tunable surface hydrophobicity, and desirable look. Therefore a wide range of studies has been performed so far to assess the diverse physical, mechanical, chemical, electrochemical, and thermal properties of electrodeposited composite coatings that are fabricated on various substrates, under different electrodeposition conditions. In particular, nickel-based composite coatings reinforced with embedded particles (e.g., oxides, carbides, nitrides, and solid-state lubricants) are among the most studied MMCs because of their industrial applications as protective and corrosion-resistant coatings with desirable wear and friction properties. In this review, we provide an extensive overview of the fabricated electrodeposited nickel-based composite coatings which are assessed for their improved wear resistance. The tribological and wear properties of the composite coatings such as weight loss, wear rate, friction coefficient, surface hardness and roughness, as well as their underlying wear mechanisms, will be discussed as a function of the type, content, size, and distribution of the reinforced particles under different electrodeposition parameters such as type and magnitude of applied current, bath composition, pH, temperature, ultrasonication, and presence of surfactants. The quantitative coating characteristics that are tabulated in this review serve as a reference for the researchers in this field and enable the quick selection of coatings and electrodeposition parameters for the desired application.
Keywords: Electrodeposition; Composite coatings; Wear; Tribology

Wear behavior of alkaline pulsed electrodeposited nickel composite coatings reinforced by ZnO nanoparticles - Sajjadnejad, Mohammad; Haghshenas, Seyyed Mohammad Saleh; Tavakoli Targhi, Vahid; Setoudeh, Nader; Hadipour, Ali; Moghanian, Amirhossein; Hosseinpour, Saman (Wear, 2021)
Nickel-ZnO nanocomposite coatings were fabricated by pulse electrodeposition in an alkaline bath. The effect of different deposition parameters such as current density, duty cycle, and pulse frequency as well as the impact of addition of 10 g/l ZnO nanoparticles into the nickel matrix on the friction behavior of fabricated coatings were investigated. X-ray diffraction, atomic force microscopy, scanning electron microscopy, microhardness test, and pin-on-disk wear test were utilized to assess the coatings characteristics, mechanical behavior, and wear resistance and a thorough comparison was performed between the pure nickel coating and its reinforced composite counterpart, with respect to their surface morphology, surface topography, and wear resistance properties. Our results indicate that by ZnO incorporation into the coating, the number of nucleation sites for nickel crystals increases, the crystal growth is retarded, and a nanocomposite coating with smaller grains can be fabricated. The incorporation of ZnO led to significantly increase in microhardness, changed the wear mechanism from adhesion to abrasion, and improved the wear rate. By increasing the electrodeposition current density (from 4 to 10 A/dm2), the wear rate was noticeably decreased while the friction coefficient was significantly enhanced. As the electrodeposition duty cycle and pulse frequency were increased to 75% and 100 Hz, respectively, wear rate of the composite coating increased noticeably as a consequence of the changes in the coating properties. The optimum electrodeposition condition for Ni–ZnO nanocomposite coatings was achieved at 10 A/dm2, γ = 50% and f = 10 Hz resulting in a coating with the lowest wear rate (3.2539 × 10−4 mm3/Nm), minimum weight loss (0.0014 gr), highest microhardness (290 Hv), maximum ZnO incorporation rate (4.04 vol% ZnO), and highest friction coefficient (0.972) among all investigated coatings. It was concluded that increasing current density improved the wear resistance while the enhancement of duty cycle and pulse frequency led to worsen it.
CRIS-Team Scopus Importer:2021-01-08
Keywords: Electrodeposition; Morphology; Nanocomposite; Nickel; Wear; ZnO

Well-separated water-soluble carbon dots via gradient chromatography - Michaud, Vanessa; Pracht, Jonas; Schilfarth, Fabian; Damm, Cornelia; Platzer, Benedikt; Haines, Philipp; Harreiß, Christina; Guldi, Dirk Michael; Spiecker, Erdmann; Peukert, Wolfgang (Nanoscale, 2021)
Carbon dots (CDs) are strongly fluorescent advanced materials that are promising for applications in bio-imaging, sensors or luminescent displays. One of the most-widely used class of CDs is synthesized via an aqueous, bottom-up technique starting from citric acid (CA) and an amino-precursor. Very high fluorescence quantum yields (QY) are reported for the resulting CDs. The as-synthesized raw suspensions, however, are crude mixtures of many components: bare carbon cores, carbon cores functionalized with fluorophores, freely floating molecular fluorophores, and several other by-products. In this study, we synthesized CDs from CA and amino acid cysteine (Cys) hydrothermally and demonstrate a complete separation of all components by means of two step gradient chromatography. In the first step, the separation was carried out on a normal-pressure preparative silica-gel column to get sufficient amounts of material to investigate structure and optical properties of the collected fractions. This preparative gradient elution method enabled us to separate moderately-fluorescent CDs from freely floating molecular fluorophores, polymeric fluorophores and CDs with built-in fluorophores. Here, we evidenced that amorphous CDs co-exist with crystalline CDs in one and the same suspension and showed that the amount of crystalline CDs increases with the synthesis temperature. In the second step, we turned to high performance liquid chromatography (HPLC) to further improve and optimize the efficiency of purification and automate it. Via HPLC, we were able to well-separate of up to six components. Within this work, we laid the foundation for CD purification with the highest possible purity for aqueous, bottom-up synthesized CDs and quantified the true quantum yield of CDs.
Keywords: Graphene quantum dots; Photoluminescence mechanism; Polymer dots; Citric-acid; Nanodots; Fluorescence; Yield; Nitrogen; Light; Reduction

Wet milling of H-ZSM-5 zeolite and its effects on direct oxidation of benzene to phenol - Gopalakrishnan, Saiprasath; Yada, S.; Münch, Jörg; Selvam, Thangaraj; Schwieger, Wilhelm; Sommer, Marc; Peukert, Wolfgang (Applied Catalysis A-General, 2007)
The direct oxidation of benzene to phenol with NO over ZSM-5 catalysts suffers from the problem of rapid catalyst deactivation mainly due to the secondary transformation of phenol into heavier hydrocarbon compounds leading to the catalyst coking. In order to investigate the deactivation behavior of the ZSM-5 catalysts during this reaction, a comparative study was performed over ZSM-5 catalysts having different crystal sizes. The original catalyst was milled to two different periods of time to obtain catalysts having various crystal sizes. The original and the milled catalysts were tested for the benzene to phenol reaction to get an insight into the effect of crystal size on the catalyst deactivation. There was a decrease in catalyst deactivation with a decrease in crystal size. An indirect dependence of catalyst deactivation with total acidity was observed. © 2007 Elsevier B.V. All rights reserved.
Keywords: Benzene oxidation; Crystal size; Microreactor; Nitrous oxide; Phenol; ZSM-5

Wet nanomilling of naproxen using a novel stabilization mechanism via zirconium complexation - Maar, Scott; Damm, Cornelia; Peukert, Wolfgang (Advanced Powder Technology, 2022)
Using a novel electrostatic stabilization mechanism that utilizes complexation of Zr(IV) species by car-boxylic acid groups at the particle surface, the true grinding limit of monocrystalline naproxen nanopar-ticles was identified at 30 nm under an optimized naproxen/Zr(IV)-salt formulation. In a stirred media mill, we studied the influence of stress energy and number of stress events by varying the milling bead diameter. Small milling beads provide a compromise between sufficiently high stress energy and stress number and are beneficial for nanomilling of naproxen in terms of grinding kinetics. It is shown that the product particle size can be controlled by adjusting the colloidal stability via the Zr(IV) concentration. Regardless of formulation properties, particle fracture propagates along the grain boundaries as revealed by crystallite size analysis. Investigations of the solvent phase and the particle geometry reveal that mechanical stress leads to enhanced solubility of the drug, which in return promotes recrystallization and thus particle growth. The solubility can be reduced by lowering the process temperature and stabi-lizer concentration. In contrast to inorganic nanoparticles, which are almost free of lattice imperfections at the true grinding limit, we find a clear indication of lattice strain in the stressed naproxen nanoparti-cles. Since the nanoparticle yield is still limited to 40% due to particle ripening, fast removal of the nanoparticles from the mill must be a further next step to be solved in nanoparticle processing.
Keywords: Grinding limit; Colloidal stability; Stirred media ball mill; Solubility; Naproxen

Wet nanomilling of naproxen using a novel stabilization mechanism via zirconium complexation - Maar, Scott; Damm, Cornelia; Peukert, Wolfgang (Advanced Powder Technology, 2022)
Using a novel electrostatic stabilization mechanism that utilizes complexation of Zr(IV) species by carboxylic acid groups at the particle surface, the true grinding limit of monocrystalline naproxen nanoparticles was identified at 30 nm under an optimized naproxen/Zr(IV)-salt formulation. In a stirred media mill, we studied the influence of stress energy and number of stress events by varying the milling bead diameter. Small milling beads provide a compromise between sufficiently high stress energy and stress number and are beneficial for nanomilling of naproxen in terms of grinding kinetics. It is shown that the product particle size can be controlled by adjusting the colloidal stability via the Zr(IV) concentration. Regardless of formulation properties, particle fracture propagates along the grain boundaries as revealed by crystallite size analysis. Investigations of the solvent phase and the particle geometry reveal that mechanical stress leads to enhanced solubility of the drug, which in return promotes recrystallization and thus particle growth. The solubility can be reduced by lowering the process temperature and stabilizer concentration. In contrast to inorganic nanoparticles, which are almost free of lattice imperfections at the true grinding limit, we find a clear indication of lattice strain in the stressed naproxen nanoparticles. Since the nanoparticle yield is still limited to 40% due to particle ripening, fast removal of the nanoparticles from the mill must be a further next step to be solved in nanoparticle processing.
CRIS-Team Scopus Importer:2022-08-12
Keywords: Colloidal stability; Grinding limit; Naproxen; Solubility; Stirred media ball mill

Wetting Behavior and Support Interactions in Imidazolium-Based Supported Ionic Liquid Phase Materials-A Systematic Study by Solid-State Nuclear Magnetic Resonance Spectroscopy - Frosch, Matthias; Tavera Méndez, Cindy Ly; Koch, Angela Barbara; Schörner, Markus; Haumann, Marco; Hartmann, Martin; Wisser, Dorothea (Journal of Physical Chemistry C, 2023)
Supported ionic liquid phase (SILP) catalysts are an extremely promising class of materials that combine advantageous concepts from both homogeneous and heterogeneous catalysis. Optimized SILP catalysts should exhibit a thin, homogeneous, and continuous film of the ionic liquid (IL) to avoid pore blocking and to ensure a good accessibility of the catalyst. Yet, the interactions between the IL and the support, which determine the formation of such a film, are still poorly understood. We investigate here in a systematic way the deposition of three imidazolium-based ILs on silica supports with different surface areas and morphologies using 1H magic angle spinning solid-state nuclear magnetic resonance spectroscopy. We demonstrate that the point of complete surface wetting can be determined by the disappearance of the 1H resonance of isolated silanol groups and that this point depends both on the textural properties of the support material and the chemical properties of the IL.1H chemical shifts also provide valuable insight into hydrogen bonding interactions within the IL and between the IL and the support. They indicate cleavage of the anion-cation hydrogen bonds upon IL deposition and the formation of new hydrogen bonds with the silica surface.
CRIS-Team WoS Importer:2023-05-26

Wetting-Controlled Localized Placement of Surface Functionalities within Nanopores - Ochs, Maria; Mohammadi, Reza; Vogel, Nicolas; Andrieu-Brunsen, Annette (Small, 2020)
In the context of sensing and transport control, nanopores play an essential role. Designing multifunctional nanopores and placing multiple surface functionalities with nanoscale precision remains challenging. Interface effects together with a combination of different materials are used to obtain local multifunctionalization of nanoscale pores within a model pore system prepared by colloidal templating. Silica inverse colloidal monolayers are first functionalized with a gold layer to create a hybrid porous architecture with two distinct gold nanostructures on the top surface as well as at the pore bottom. Using orthogonal silane- and thiol-based chemistry together with a control of the wetting state allows individual addressing of the different locations within each pore resulting in nanoscale localized functional placement of three different functional units. Ring-opening metathesis polymerization is used for inner silica-pore wall functionalization. The hydrophobized pores create a Cassie–Baxter wetting state with aqueous solutions of thiols, which enables an exclusive functionalization of the outer gold structures. In a third step, an ethanolic solution able to wet the pores is used to self-assemble a thiol-containing initiator at the pore bottom. Subsequent controlled radical polymerization provides functionalization of the pore bottom. It is demonstrated that the combination of orthogonal surface chemistry and controlled wetting states can be used for the localized functionalization of porous materials.
CRIS-Team Scopus Importer:2020-03-27
Keywords: colloidal monolayers; nanolocal functionalization; nanopores; surface functionalization; wetting

When Fewer Photons Do More: A Comparative O2 Photoadsorption Study on Vapor-Deposited TiO2 and ZrO2 Nanocrystal Ensembles - Siedl, Nicolas; Elser, Michael J.; Halwax, Erich; Bernardi, Johannes; Diwald, Oliver (Journal of Physical Chemistry C, 2009)
The charge separation properties of TiO_2 and ZrO_2 nanocrystal powders which were produced by metal organic chemical vapor phase deposition were compared by means of O_2 photoadsorption. Prior to the UV excitation experiments, we carefully explored the structure and morphology as well as the spectroscopic properties of the dehydroxylated nanoparticles in controlled gas atmospheres using UV diffuse reflectance, FT-IR, and electron paramagnetic resonance spectroscopy. On the basis of this information, we utilized the photogeneration of surface-adsorbed O_2- radicals and their detection by EPR spectroscopy to quantify the concentration of separated charges and to relate these figures to the number of oxide particles that were exposed to known numbers of UV photons with defined energies. The results presented in this study reveal that upon band-gap excitation, ZrO_2 nanoparticles are by 2 orders of magnitude more efficient in oxygen-assisted charge separation than TiO_2. The dramatically diminished charge separation yield in TiO_2 is attributed to the existence of deep trap states which persistently stabilize paramagnetic holes and at the same time act as recombination centers. Their absence in ZrO_2 nanocrystals gives rise to a comparable performance in terms of photoadsorbed O_2 and essentially compensates for the significantly wider optical band gap in relation to TiO_2.
EAM Import::2019-03-12

Whey protein (amyloid)-aggregates in oil-water systems: The process-related comminution effect - Heyn, Timon R.; Uttinger, Maximilian; Kwade, Arno; Peukert, Wolfgang; Keppler, Julia K.; Schwarz, Karin (Journal of Food Engineering, 2021)
Whey protein fibrils are excellent emulsifiers. However, the emulsification process significantly alters the size of the aggregates and thus their functionality. It is not yet known how strongly the disperse phase (oil) contributes to the size change. Furthermore, it is unknown whether the aggregate morphologies (semi-flexible amyloid-, and flexible amyloid-like aggregates) differ in their size reduction during emulsification. Therefore, both types of aggregates were processed under different stress levels and in the presence and absence of an oil phase by rotor-stator dispersion, ultrasonication and high-pressure homogenisation. The size reduction exponent for each aggregate type was determined by atomic force microscopy, analytical ultracentrifugation and dynamic light scattering. Semi-flexible fibrils decreased in length by rotor-stator shear from 6200 to a minimum of 190 nm, but sonication resulted in even greater shortening (150 - 84 nm) and is comparable to high pressure homogenisation (283 - 111 nm). Worm-like flexible aggregates are only affected by sonication (98 - 46 nm). The addition of oil resulted in a further reduced aggregate length with lower energy input for all aggregates. Overall, these results provide new insights about the emulsion processing behaviour of different amyloid aggregates, which should be taken into account when preparing emulsions
Keywords: Length reduction; Processing; Emulsification; Fibrils; Rotor-stator shear; Beta-lactoglobulin; Amyloid aggregates

X-Ray Computed Tomography - A Non-intrusive Technique to Characterize Local Solids Distribution in a Circulating Fluidized Bed (CFB). - Wirth, Karl-Ernst; Graßler, Thomas (Circulating Fluidized Bed Technology VI, 1999)
UnivIS-Import:2015-04-20:Pub.1999.tech.ITC.mechve.xrayco_41
Keywords: fluidized; bed; circculation; Wirbelschichtfeuerung; Wirbelschichtreaktor

X-Ray Computed Tomography in Mechanical Engineering - a Non intrusive Technique to Characterize Vertical Multiphase Flows - Wirth, Karl-Ernst; Graßler, Thomas (Computerized Tomography for Industrial Applications and Image Processing in Radiology, 1999)
UnivIS-Import:2015-04-16:Pub.1999.tech.ITC.mechve.xrayco_64