Investigation of the Relationship between the 2D and 3D Box-Counting Fractal Properties and Power Law Fractal Properties of Aggregates - Wang, Rui; Singh, Abhinandan Kumar; Kolan, Subash Reddy; Tsotsas, Evangelos (Multimodal Technologies and Interaction, 2022)
The fractal dimension has been widely used to describe the structural and morphological characteristics of aggregates. Box-counting (BC) and power law (PL) are the most common methods to calculate the fractal dimension of aggregates. However, the prefactor , as another important fractal property, has received less attention. Furthermore, there is no relevant research about the BC prefactor ( ). This work applied a tunable aggregation model to generate a series of three-dimensional aggregates with different input parameters (power law fractal properties: and , and the number of primary particles ). Then, a projection method is applied to obtain the 2D information of the generated aggregates. The fractal properties ( and ) of the generated aggregates are estimated by both, for 2D and 3D BC methods. Next, the relationships between the box-counting fractal properties and power law fractal properties are investigated. Notably, 2D information is easier achieved than 3D data in real processes, especially for aggregates made of nanoparticles. Therefore, correlations between 3D BC and 3D PL fractal properties with 2D BC properties are of potentially high importance and established in the present work. Finally, a comparison of these correlations with a previous one (not considering ) is performed, and comparison results show that the new correlations are more accurate<br

Investigation of the size-property relationship in CuInS2 quantum dots - Akdas, Tugce; Walter, Johannes; Segets, Doris; Distaso, Monica; Winter, Benjamin; Birajdar, Balaji; Spiecker, Erdmann; Peukert, Wolfgang (Nanoscale, 2015)
In this work we investigated fundamental properties of CuInS2 quantum dots in dependence of the particle size distribution (PSD). Size-selective precipitation (SSP) with acetone as poor solvent was performed as an adequate post-processing step. Our results provide deep insight into the correlation between particle size and various optical characteristics as bandgap energy, absorption and emission features and the broadness of the emission signal. These structure-property relationships are only achieved due to the unique combination of different analytical techniques. Our study reveals that the removal of 10 wt% of smallest particles from the feed results in an enhancement of the emission signal. This improvement is ascribed to a decreased quenching of the emission in larger particles. Our results reveal the impact of PSDs on the properties and the performance of an ensemble of multicomponent QDs and anticipate the high potential of controlling PSDs by well-developed post-processing.

In vitro reactivity of Cu doped 45S5 Bioglass® derived scaffolds for bone tissue engineering - Hoppe, Alexander; Meszaros, Robert; Staehli, Christoph; Romeis, Stefan; Schmidt, Jochen; Peukert, Wolfgang; Marelli, Benedetto; Nazhat, Showan N.; Wondraczek, Lothar; Lao, Jonathan; Jallot, Edouard; Boccaccini, Aldo R. (Journal of Materials Chemistry B, 2013)
Cu-doped 45S5 bioactive glasses with varying Cu contents were fabricated and used to process 3D porous scaffolds via the foam replica technique. Cu-doping results in the weakening of the glass network and a decrease in its glass transition temperature. Acellular in vitro studies revealed very high bioactivity independent of Cu doping as indicated by the fast formation of a carbonated hydroxyapatite layer (CHA) on scaffold surfaces after immersion in simulated body fluid (SBF). The kinetics of the glass-ceramic scaffold's transition to an amorphous calcium phosphate layer (ACP) and the crystallisation of CHA were explored by FT-IR and SEM analyses. The elemental distribution in the scaffold/fluid interface region was monitored by the advanced micro-PIXE-RBS (particle induced X-ray emission/Rutherford backscattering spectrometry) method. Cu-containing glasses showed slower release of Si, Ca and P from the scaffold periphery, whereas traces of Cu were found incorporated in the CaP layer on the scaffold surface. Cu release kinetics from the scaffolds in SBF were found to depend on culturing conditions while highest Cu concentrations of ∼3.1 ppm and ∼4.6 ppm under static and quasi-dynamic conditions, respectively, were observed. Since Cu exhibits potential angiogenic and osteogenic properties, the Cu-containing scaffolds are suggested as promising materials for bone tissue engineering applications. © 2013 The Royal Society of Chemistry.
UnivIS-Import:2015-03-09:Pub.2013.tech.IW.LM.invitr_2

Ionic-Liquid-Infused Nanostructures as Repellent Surfaces - Galvan, Yaraset; Phillips, Katherine R.; Haumann, Marco; Wasserscheid, Peter; Zarraga, Ramon; Vogel, Nicolas (Langmuir, 2018)
In order to prepare lubricant-infused repellent coatings on silica nanostructures using low vapor pressure ionic liquids as lubricants, we study the wetting behavior of a set of imidazolium-based ionic liquids with different alkyl side chains as a function of the applied surface functionalities. We take advantage of the structural color of inverse opals prepared from a colloidal coassembly technique to study the infiltration of ionic liquids into these nanoporous structures. We find that the more hydrophobic ionic liquids with butyl and hexyl side chains can completely infiltrate inverse opals functionalized with mixed self-assembled monolayers composed of imidazole groups and aliphatic hydrocarbon chains, which we introduce via silane chemistry. These molecular species reflect the chemical nature of the ionic liquid, thereby increasing the affinity between the liquid and solid surface. The mixed surface chemistry provides sufficiently small contact angles with the ionic liquid to infiltrate the nanopores while maximizing the contact angle with water. As a result, the mixed monolayers enable the design of a stable ionic liquid/solid interface that is able to repel water as a test liquid. Our results underline the importance of matching chemical affinities to predict and control the wetting behavior in complex, multiphase systems
Keywords: Coating materials; Salts; Liquids; Wetting; Solvents

Ionomer and protein size analysis by analytical ultracentrifugation and electrospray scanning mobility particle sizer - Wawra, Simon; Thoma, Martin; Walter, Johannes; Lübbert, Christian; Thajudeen, Thaseem; Damm, Cornelia; Peukert, Wolfgang (European Biophysics Journal, 2018)
Keywords: Analytical ultracentrifugation; Scanning mobility particle sizer; Combined analysis; Multiwavelength detector

Iron Precursor Decomposition in the Magnesium Combustion Flame: A New Approach for the Synthesis of Particulate Metal Oxide Nanocomposites - Gheisi, Amirreza; Niedermaier, Matthias; Tippelt, Gerold; Lottermoser, Werner; Bernardi, Johannes; Diwald, Oliver (Particle & Particle Systems Characterization, 2017)
Powders of Fe–Mg–O nanocomposite particles have been grown using a novel chemical vapor synthesis approach that employs the decomposition of a metalorganic precursor inside the metal combustion flame. After annealing in controlled gas atmospheres composition distribution functions, structure and phase stability of the obtained magnesiowüstite nanoparticles are measured with a combination of techniques such as inductively coupled plasma‐optical emission spectroscopy, energy dispersive X‐ray spectroscopy, X‐ray diffraction, and scanning and transmission electron microscopy. Complementary Mössbauer spectroscopy measurements reveal that depending on Fe loading and temperature of annealing either metastable and superparamagnetic solid solutions of Fe3+ ions in periclase (MgO) or phase separated mixtures of MgO and ferrimagnetic magnesioferrite (MgFe2O4) nanoparticles can be obtained. The described combustion technique represents a novel concept for the production of mixed metal oxide nanoparticles. Adressing the impact of selected annealing protocols, this study underlines the great potential of vapor phase grown non‐equilibrium solids, where thermal processing provides means to trigger phase separation and, concomitantly, the emergence of new magnetic propertie
Keywords: metal oxide nanoparticles; metastability; ferrimagnetism; iron admixture; phase separation; combustion synthesis

Isoelectric Point of Proteins at Hydrophobic Interfaces - Lautenbach, Vanessa; Hosseinpour, Saman; Peukert, Wolfgang (Frontiers in Chemistry, 2021)
Structural and colloidal stability of proteins at different surfaces and interfaces is of great importance in many fields including medical, pharmaceutical, or material science. Due to their flexibility, proteins tend to respond to their environmental conditions and can undergo structural and conformational changes. For instance, alterations in physiological factors such as temperature, ions concentration, or pH as well as the adsorption to an interface can initiate protein aggregation. Therefore, at different surfaces and interfaces the characterization of the structural and colloidal stability of proteins, which is mainly influenced by their electrostatic and hydrophobic interactions, is of fundamental importance. In this study, we utilized sum frequency generation (SFG) spectroscopy to assess the role of solution pH on the polarity and magnitude of the electric field within the hydration shell of selected model proteins adsorbed to a hydrophobic surface. We used polystyrene (PS) as a model hydrophobic surface and determined the isoelectric point (IEP) of four structurally different model proteins. Comparing the measured IEP of proteins at the PS/solution or air/solution interface with that determined in the bulk solution via zeta potential measurement, we found significant similarities between the IEP of surface adsorbed proteins and those in the bulk aqueous phase. The pH dependence behavior of proteins was correlated to their amino acid composition and degree of hydrophobicit
Keywords: proteins; isoelectric point; sum frequency generation spectroscopy; surface hydrophobicity; zeta potential

Isoelectric points of proteins at the air/liquid interface and in solution - Guckeisen, Tobias; Hosseinpour, Saman; Peukert, Wolfgang (Langmuir, 2019)
Electrostatic interactions play essential roles in determining the function, colloidal stability, and adsorption of proteins on different surfaces and interfaces. Therefore, a molecular level understanding of the charge state of the proteins under different conditions is required to explain their macroscopic properties. In this study we have employed an inherently surface sensitive spectroscopic tool, sum frequency generation spectroscopy, to determine the charge state of a wide range of proteins as a function of pH at the liquid/air interface via measurement of the degree of orientation of water molecules. We compared the isoelectric point of the 12 investigated proteins at the liquid/air interface with that in the bulk solution obtained through zeta potential measurements. Ellipsometry is performed to determine the film thickness at the liquid/air interface at different charge states. In particular, protein aggregation at the isoelectric point is reflected by increased film thickness. For all proteins, the interfacial point of zero charge is close (with less than 1 pH unit variation) to that in the bulk solution.
Keywords: protein; potential; charge; surface

Isolation and Purification of Single Gold Nanoclusters by Alternate Pumping Chromatography - Supper, Malvina; Birner, Virginia; Gromotka, Lukas; Peukert, Wolfgang; Kaspereit, Malte (Separations, 2023)
Alternate pumping chromatography is applied to obtain atomically precise glutathione-stabilized gold nanoclusters in high purity from synthesized mixtures. On the basis of anion exchange chromatography, the feasibility of isolating a single cluster, Au10 GSH10, as well as two different clusters simultaneously (Au25 GSH18 and Au29 GSH20) is demonstrated. In addition, Au18 GSH14, which is present only in trace amounts, is successfully enriched. A simple design procedure is proposed that allows using columns with different retention behavior. Successful experiments with large injection amounts confirm the potential of the concept for preparative-scale productions of high-quality nanoparticulate product

Kernel identification in continuous fluidized bed spray agglomeration from steady state data - Otto, Eric; Dürr, Robert; Strenzke, Gerd; Palis, Stefan; Bück, Andreas; Tsotsas, Evangelos; Kienle, Achim (Advanced Powder Technology, 2021)
Fluidized bed spray agglomeration is an important industrial particle formation process. In particular, the continuous operation mode is able to provide a constant stream of product particles with constant quality in terms of particle properties. Mathematical process modeling represents a valuable tool for a thorough analysis of the involved mechanistic processes and can further be used for process intensification and control. Sophisticated models describing the quantitative effect of process conditions on particle properties are particularly important. Therefore, in this contribution the influence of the seven most important operational parameters on the particle size distribution is modeled, including fluidization and binder properties. To this end, a population balance process model with the three-parametric Kapur kernel is fitted to experimental data. The first main result of this contribution is the quantitative description of the dependency between the agglomeration rate and the process conditions by multidimensional paraboloids. The second main result is the introduction of a general method by which this quantitative formulation is obtained.
CRIS-Team Scopus Importer:2021-06-18
Keywords: Agglomeration kernel; Continuous spray agglomeration; Kapur kernel; Parameter identification; Population balance equation

Key Role of Binders to Anchor Nanoparticle-Based Supraparticles on Spherical Substrates with Preserved Functionality - Zimmermann, Thomas; Fischer, Christopher; Oppmann, Maximilian; Wenderoth, Sarah; Winzer, Bettina; Somorowsky, Ferdinand; Vogel, Nicolas; Mandel, Karl; Wintzheimer, Susanne (ACS Applied Nano Materials, 2025)
Supraparticles, particles composed of individual nanoparticles, have attractive properties, but their applicability in real-world applications is often restricted by their comparably small dimensions. Suprabeads, in which individual supraparticles are fixed to a larger support bead with the help of a binder, have been proposed to address this challenge. These suprabeads retain the the unique functionalities of both the nanoparticles and supraparticles while offering millimeter-sized dimensions for facilitated handling. Here, we investigate the role of the binder in the formation and functionalization of suprabeads. First, we focus on the thermal, mechanical, and chemical stabilities of suprabeads as a function of their binder composition. Our results show that binders containing organic groups offer room-temperature curability, while the chemical and thermal stability of the resulting suprabeads is limited and their mechanical stability depends on the flexibility of the binder. Inorganic binders drastically increase the temperature stability but are inherently more brittle. Second, we demonstrate that wetting the supraparticle with the binder layer enables us to tailor the resultant suprabead functionality. While a low degree of embedding provides accessible supraparticles, a larger degree of embedding induces tunable protection of the supraparticles from the environment. To highlight the versatility of the suprabead concept, we demonstrate that the ideal binder material can be identified for a specific application, such as ammonia indication or propane dehydrogenation.
CRIS-Team Scopus Importer:2025-02-28
Keywords: binder; gas detection; mechanical stability; suprabeads; supraparticles

Kinetics of radical formation during the mechanical activation of quartz - Damm, Cornelia; Peukert, Wolfgang (Langmuir, 2009)
The kinetics of radical formation during the mechanical activation of quartz by wet grinding or sonication was investigated using 2,2-diphenyl-1- picrylhydrazyl (DPPH) as a scavenger. The consumption of DPPH during the sonication of quartz in an ethanol suspension is a zeroth-order process. A linear relationship between the rate constant of the DPPH consumption and the quartz concentration in the suspension indicates that radical formation under sonication increases with the growing total surface area of the quartz particles. Sonication leads to the formation of free radicals by the mechanical activation of the particle surface. The kinetics of the DPPH consumption during wet grinding of quartz in a stirred media mill is described successfully by a modified zeroth-order rate law taking the total surface area of the quartz particles into account. The surface-normalized rate constant of the DPPH consumption decreases from 1.8 × 10 mol L h m to 4.8 × 10 mol L h m if the specific surface area of the feed material increases from 0.5 to 84 m/g. This finding indicates that the breakage of the quartz particles contributes much more to radical formation than does the mechanical activation of the particles in the mill because the breakage rate increases with growing particle diameter. Ethanol but not DPPH was found on the surface of the ground quartz particles. From this finding, it can be concluded that radicals on the surface of the quartz particles react with ethanol, leading to the formation of ethanol radicals and H radicals. DPPH reacts with the H radicals. As a side reaction, radicals can react with oxygen, leading to the formation of peroxides. © Copyright 2009 American Chemical Society.

Kunststoffpulver für die Additive Fertigung: Vorhersage des Prozessverhaltens mittels prozessangepasster Analyse / Plastic powder for Additive Manufacturing: Prediction of process behavior based on process adapted characterization - Wudy, Katrin; Schmidt, Jochen; Lanzl, Lydia; Zhao, Meng; Jaksch, Andreas; Dechet, Maximilian; Hesse, Nicolas; Drummer, Dietmar; Peukert, Wolfgang (Vom Pulver zum multifunktionalen Bauteil, 2019)

Large-Area 3D Plasmonic Crescents with Tunable Chirality - Görlitzer, Eric; Mohammadi, Reza; Nechayev, Sergey; Banzer, Peter; Vogel, Nicolas (Advanced Optical Materials, 2019)
Chiral plasmonic nanostructures hold promise for enhanced chiral sensing and circular dichroism spectroscopy of chiral molecules. It is therefore of interest to fabricate chiral plasmonic nanostructures with tailored chiroptical properties over large areas with reasonable effort. Here, a colloidal lithography approach is used to produce macroscopic arrays of sub-micrometer 3D chiral plasmonic crescent structures over areas >1 cm 2 . The chirality originates from symmetry breaking by the introduction of a step within the crescent structure. This step is produced by an intermediate layer of silicon dioxide onto which the metal crescent structure is deposited. It is experimentally demonstrated that the chiroptical properties in such structures can be tailored by changing the position of the step within the crescent. These experiments are complemented by finite element simulations and the application of a multipole expansion to elucidate the physical origin of the circular dichroism of the crescent structures.
CRIS-Team Scopus Importer:2019-06-04
Keywords: chirality; colloidal lithography; multipole decomposition; plasmonics; split-ring resonator

Large-Scale Synthesis of Highly Uniform Silicon Nanowire Arrays Using Metal-Assisted Chemical Etching - Wendisch, Fedja J.; Rey, Marcel; Vogel, Nicolas; Bourret, Gilles Remi (Chemistry of Materials, 2020)
The combination of metal-assisted chemical etching (MACE) with colloidal lithography has emerged as a simple and cost-effective approach to nanostructure silicon. It is especially efficient at synthesizing Si micro- and nanowire arrays using a catalytic metal mesh, which sinks into the silicon substrate during the etching process. The approach provides a precise control over the array geometry, without requiring expensive nanopatterning techniques. Although MACE is a high-throughput solution-based approach, achieving large-scale homogeneity can be challenging because of the instability of the metal catalyst when the experimental parameters are not set appropriately. Such instabilities can lead to metal film fracture, significantly damaging the substrate and thus compromising the nanowire array quality. Here, we report on the critical parameters that influence the stability of the metal catalyst layer for achieving large-scale homogeneous MACE: etchant composition, metal film thickness, adhesion layer thickness, nanowire diameter and pitch, metal film coverage, Si/Au/etchant interface length, and crystalline quality of the colloidal template (grain size and defects). Our results investigate the origin of the catalyst film fracture and reveal that MACE experiments should be optimized for each Si wire array geometry by keeping the etch rate below a certain threshold. We show that the Si/Au/etchant interface length also affects the etch rate and should thus be considered when optimizing the MACE experimental parameters. Finally, our results demonstrate that colloidal templates with small grain sizes (i.e., <100 μm2) can yield significant problems during the pattern transfer because of a high density of defects at the grain boundaries that negatively affects the metal film stability. As such, this work provides guidelines for the large-scale synthesis of Si micro- and nanowire arrays via MACE, relevant for both new and experienced researchers working with MAC
Keywords: Etching; Metals; Gold; Nanowire arrays; Silicon

Laser-Activated Self-Assembled Thermoplasmonic Nanocavity Substrates for Intracellular Delivery - Madrid, Marinna; Saklayen, Nabiha; Shen, Weilu; Huber, Marinus; Vogel, Nicolas; Mazur, Eric (ACS Applied Bio Materials, 2018)
Intracellular delivery is crucial for cellular engineering and the development of therapeutics. Laser-activated thermoplasmonic nanostructured surfaces are a promising platform for high-efficiency, high-viability, high-throughput intracellular delivery. Their fabrication, however, typically involves complicated nanofabrication techniques, limiting the approach's applicability. Here, colloidal self-assembly and templating are used to fabricate large arrays of thermoplasmonic nanocavities simply and cost-effectively. These laser-activated substrates are used to deliver membrane-impermeable dye into cells at an efficiency of 78% and throughput of 30â»000 cells min-1 while maintaining 87% cell viability. Proof-of-concept data show delivery of large cargoes ranging from 0.6 to 2000 kDa to cells without compromising viability.
CRIS-Team Scopus Importer:2023-03-29
Keywords: colloidal templating; intracellular delivery; pulsed lasers; self-assembly; thermoplasmonics

Laser Beam Melting in Powder Bed of nonspherical aluminium microparticles dry coated with metal nanoparticles - Karg, Michael; Ahuja, Bhrigu; Schmidt, Jochen; Winzer, Bettina; Wirth, Karl-Ernst; Peukert, Wolfgang; Schmidt, Michael (Proceedings [Elektronski vir] / 6th International Conference on Additive Technologies iCAT2016, 2016)
Out of all Al alloys, Laser Beam Melting in Powder Bed (LBM) is almost exclusively used to process Al-Si cast alloys today. Feasibility of LBM of high-performance Al-Cu wrought alloys was published previously by the authors. Prealloyed powders are used for LBM. Small amounts or less common application-specific alloys must be atomized on request which is expensive, time consuming and of varying quality. Instead, during LBM alloys might form from mixtures of few basic powders. If density differs strongly as e. g. with Al and Cu, powders de-mix uncontrollably due to gravity. In LBM, spherical inert gas atomized powders are used. Cheaper non-spherical air atomized Al powders deposit insufficiently homogeneous in thin powder layers. LBM of Metal Matrix Composites (MMC) was shown using mechanical alloying that was time-consuming, affected particle size and shape. The goal of this contribution is to investigate the feasibility of an approach towards larger freedom of choice in LBM regarding all aforementioned dimensions of alloy composition, MMC creation and non-spherical base powders. Metal nanoparticles (np) were dry coated onto air atomized Al alloy micro particles. Powders with adhering np and LBM products were analyzed and compared to previous results.</
Keywords: metal nanoparticle adhesion; air atomized aluminium powder Metal Matrix Composite MMC; in-situ alloying; Selective Laser Melting SLM; powder bed fusion

Lasergestützte Verbindungstechnik für räumliche, spritzgegossene Schaltungsträger (3D-MID) für Gebrauchstemperaturen über 150°C - Eßer, Gerd; Horn, Michael (PLUS-Produktion von Leiterplatten und Systemen, 2003)
LFT Import::2019-07-15 (988)

Laser Spot Welding and Soldering of Micro Components to 3-Dimensional Circuit Substrates - Ostendorf, A.; Kulik, C.; Zeadan, M.; Schmidt, Michael; Horn, Michael (5th International Congress on Molded interconnect Devices (MID), 2002)
LFT Import::2019-08-05 (1716)

Laterally patterned ultraflat surfaces - Vogel, Nicolas; et al. (Small, 2009)
Keywords: Electrodes; Lithography; Patterning; Self-assembled monolayers; Surfaces

Layer-by-Layer Assemblies of Catechol-Functionalized TiO2 Nanoparticles and Porphyrins through Electrostatic Interactions - Burger, Alexandra; Costa, Ruben Dario; Lobaz, Volodymyr; Peukert, Wolfgang; Hirsch, Andreas; Guldi, Dirk Michael (Chemistry - A European Journal, 2015)
In the current work, we present the successful functionalization and stabilization of P-25 TiO2 nanoparticles by means of N1,N7-bis(3-(4-tert-butyl-pyridium-methyl)phenyl)-4-(3-(3-(4-tert-butyl-pyridinium-methyl)phenylamino)-3-oxopropyl)-4-(3,4-dihydroxybenzamido)heptanediamide tribromide (1). The design of the latter is aimed at nanoparticle functionalization and stabilization with organic building blocks. On one hand, 1 features a catechol anchor to enable its covalent grafting onto the TiO2 surface, and on the other hand, positively charged pyridine groups at its periphery to prevent TiO2 agglomeration through electrostatic repulsion. The success of functionalization and stabilization was corroborated by thermogravimetric analysis, dynamic light-scattering, and zeta potential measurements. As a complement to this, the formation of layer-by-layer assemblies, which are governed by electrostatic interactions, by alternate deposition of functionalized TiO2 nanoparticles and two negatively charged porphyrin derivatives, that is, 5,10,15,20-(phenoxyacetic acid)-porphyrin (2) and 5,10,15,20-(4-(2-ethoxycarbonyl)-4-(2-phenoxyacetamido)heptanedioic acid)-porphyrin (3), is documented. To this end, the layer-by-layer deposition is monitored by UV/Vis spectroscopy, scanning electron microscopy, ellipsometry, and profilometry techniques. The resulting assemblies are utilized for the construction and testing of novel solar cells. From stable and repeatable photocurrents generated during several ön-offc̈ycles of illumination, we derive monochromatic incident photo-to-current conversion efficiencies of around 3 \

Levitating the future: light, magnet, and fiber unite - Chakraborty, Soumya; Wong, Gordon Kwan Leung; Oda, Ferdi; Wachter, Vanessa; Kusminskiy, Silvia Viola; Yokosawa, Tadahiro; Hübner, Sabine; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Distaso, Monica; Russell, Philip St. J.; Joly, Nicolas (Proceedings Volume PC12991, Nanophotonics X, 2024)
We report the first-ever observation of optomagnetically-driven rotation of a magnetic particle, optically levitated inside a chiral hollow-core photonic crystal fibre (HC-PCF). Rotation of the optically biaxial particle causes a change in the transmitted power and ellipticity of a linearly polarised probe beam at 632.8 nm. HC-PCF offers a versatile platform for investigating the optomechanical response of levitated magnetic particle

Ligand-assisted thickness tailoring of highly luminescent colloidal CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets - Levchuk, Ievgen; Herre, Patrick; Brandl, Marco; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Schweizer, Peter; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph (Chemical Communications, 2017)
Quantum size-confined CHNHPbX (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

Light interaction between gold nanoshells plasmon resonance and planar optical waveguides - Lal, Surbhi; Westcott, Sarah; Klupp Taylor, Robin; Jackson, Joseph; Nordlander, Peter; Halas, Naomi (Journal of Physical Chemistry B, 2002)
We have studied the experimental and theoretical aspects of the interaction of gold nanoshells on a waveguiding structure. Gold nanoshells are core−shell particles consisting of a silica core surrounded by a thin gold shell. The waveguiding structure consists of a 2 μm thick layer of gold with a dielectric layer of varying thickness deposited on it. Light scattering experiments performed on gold nanoshells randomly deposited on the dielectric layer show a change in the scattering spectrum of the nanoshells because of coupling of light with the waveguide modes. Comparison of experimental data with theoretical calculations based on the classic theory of point dipoles placed over a conducting surface shows a significant shift in the dipole resonance position. A simple image charge calculation taking into consideration finite size effects explains the red shift observed in the experimental data for the smallest dielectric layer thickness. Observed deviations from the theoretical models are attributable to nanoshell aggregate
Keywords: plasmon; nanoparticle; optics; shell; core; particle

Light matters: Quantifiable optical interaction between near-infrared laser radiation and nano-additivated polymers in all states of matter present in laser powder bed fusion - Sommereyns, Alexander; Leupold, Simon; Rudlof, Frederic; Willeke, Michael; Ghosh, Anindya; Ohannessian, Ben; Merwin, Daniella; Elahi, Reza; Barcikowski, Stephan; Vogel, Nicolas; Schmidt, Michael (Additive Manufacturing, 2024)
Comprehending the interaction between light and material is crucial to the success of various laser-based processes, including laser powder bed fusion of polymers. The use of the promising near-infrared laser wavelength in laser powder bed fusion of polymers is limited by the need for absorption-enhancing (nano-) additives and insufficient knowledge of the (nano-) particulate impact on the material and process behavior. The presented study lays the groundwork for an improved understanding of the laser-material interaction at different states of matter in laser powder bed fusion by means of thermo-optical measurements with a double integrating sphere setup. The authors characterize polyamide 12 and its nanocomposite powder surface-coated with carbon black nanoparticles by two different additivation methods. The attenuation coefficient and penetration depth of each material were calculated based on the measured transmittance and reflectance in all relevant states of matter. The effects of the feedstock particle size, the nano-additivation method, and the nanoparticle quantity were evaluated. The optical results of resolidified samples were validated using a commercially available spectrophotometer. Finally, the authors were able to qualitatively correlate the thermo-optical results with the depth of fusion of specimens processed at 808 nm.<br
Keywords: laser powder bed fusion; polymer nanocomposite; thermo-optical property; near-infrared laser; attenuation coefficient

Liquid filtration of nanoparticles through track-etched membrane filters under unfavorable and different ionic strength conditions: Experiments and modeling - Peukert, Wolfgang; Segets, Doris; Süß, Sebastian; Chen, Sheng-Chieh; Pui, David; Lee, Handol (Journal of Membrane Science, 2017)
Nanoparticle deposition experiments under unfavorable conditions were conducted experimentally and theoretically. The 0.2 and 0.4 µm rated track-etched membrane filters were challenged with 60, 100, 147, 220, 350 and 494 nm polystyrene latex (PSL) particles with different ionic strengths ranging from 0.005 to 0.05 M. The capillary tube model, with replacing the viscosity of air to water, was used to estimate the initial efficiency, or the transport efficiency of the particles to the filter surface, which was corrected in a second step by allowing the detachment of the nanoparticles according to the sum of adhesive and hydrodynamic torques. The adhesive torques were derived from surface interactions accessed by the extended DLVO theory. Calculation results showed that the adhesive torque of a particle located in the calculated primary minimum was slightly larger than the hydrodynamic torque, resulting in particle deposition. However, experimental data clearly indicated that detachment occurred. This could only be explained by the presence of additional hydration forces, leading to a larger separation which became relevant at high ionic strengths. By including hydration into our theoretical framework, experiment and theory were in very good agreement under all different ionic strength conditions. The findings allow a basic understanding of surface interactions between nanoparticles and membranes in micro- and ultra-filtration applications for drinking water production, wastewater treatment and particle free water production in industries.
Keywords: Adhesive and hydrodynamic torque; Derjaguin-Landau-Verwey-Overbeek (DLVO) theory; Microfiltration; Short range hydration effects; Track-etched polycarbonate membrane filter

Liquid phase temperature determination in dense water sprays using linear Raman scattering - Hankel, Robert; Günther, Astrid; Wirth, Karl-Ernst; Leipertz, Alfred; Bräuer, Andreas (Optics Express, 2014)

Local densification of a single micron sized silica sphere by uniaxial compression - Romeis, Stefan; Paul, Jonas; Herre, Patrick; de Ligny, Dominique; Schmidt, Jochen; Peukert, Wolfgang (Scripta Materialia, 2015)

London-van der Waals adhesiveness of rough particles - Lin, Qi; Rudolph, Victor; Peukert, Wolfgang (Powder Technology, 2006)
Van der Waals forces often dominate interactions and adhesion between fine particles and, in turn, decisively influence the bulk behaviour of powders. However, so far there is no effective means to characterize the adhesive behaviour of such particles. A complication is that most powder particles have rough surfaces, and it is the asperities on the surfaces that touch, confounding the actual surface that is in contact. Conventional approaches using surface energy provide limited information regarding adhesion, and pull-off forces measured through atomic force microscope (AFM) are highly variable and difficult to interpret. In this paper we develop a model which combines the Rumpf-Rabinovich and the JKR-DMT theories to account simultaneously for the effects of surface roughness and deformation on adhesion. This is applied to a 'characteristic asperity' which may be easily obtained from AFM measurements. The concept of adhesiveness, a material property reflecting the influences of elastic deformability, surface roughness, and interfacial surface energy, is introduced as an efficient and quantitative measure of the adhering tendency of a powder. Furthermore, a novel concept of specific adhesiveness is proposed as a convenient tool for characterizing and benchmarking solid materials. This paper provides an example to illustrate the use of the proposed theories. © 2005 Elsevier B.V. All rights reserve
Keywords: Adhesion; Adhesiveness; Effective contact area; Fine particles; Specific adhesiveness; Van der Waals force

Longitudinal eigenvibration of multilayer colloidal crystals and the effect of nanoscale contact bridges - Ghanem, Maroun Abi; Khanolkar, Amey; Wallen, Samuel P.; Helwig, Mary; Hiraiwa, Morgan; Maznev, Alexei A.; Vogel, Nicolas; Boechler, Nicholas (Nanoscale, 2019)
Longitudinal contact-based vibrations of colloidal crystals with a controlled layer thickness are studied. These crystals consist of 390 nm diameter polystyrene spheres arranged into close packed, ordered lattices with a thickness of one to twelve layers. Using laser ultrasonics, eigenmodes of the crystals that have out-of-plane motion are excited. The particle-substrate and effective interlayer contact stiffnesses in the colloidal crystals are extracted using a discrete, coupled oscillator model. Extracted stiffnesses are correlated with scanning electron microscope images of the contacts and atomic force microscope characterization of the substrate surface topography after removal of the spheres. Solid bridges of nanometric thickness are found to drastically alter the stiffness of the contacts, and their presence is found to be dependent on the self-assembly process. Measurements of the eigenmode quality factors suggest that energy leakage into the substrate plays a role for low frequency modes but is overcome by disorder- or material-induced losses at higher frequencies. These findings help further the understanding of the contact mechanics, and the effects of disorder in three-dimensional micro- and nano-particulate systems, and open new avenues to engineer new types of micro- and nanostructured materials with wave tailoring functionalities via control of the adhesive contact properties.
CRIS-Team WoS Importer:2019-05-17

Low temperature formation of CuIn1 - xGaxSe2solar cell absorbers by all printed multiple species nanoparticulate Se + Cu-In + Cu-Ga precursors - Möckel, Stefan; Wernicke, Tobias; Arzig, Matthias; Köder, Philipp; Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Peukert, Wolfgang; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2015)
In this work an all nanoparticulate precursor for application in Cu(InGa)Sesolar cell absorbers is presented. Binary Cu-In nanoparticles, Cu-Ga powder and elemental Se nanoparticles were mixed in dispersion and deposited on Mo-coated substrates. Research was focused on Cu(InGa)Selayer formation kinetics, phase composition characterised by differential scanning calorimetry and in-situ X-ray diffraction (XRD). Furthermore phase composition and morphology were studied by ex-situ XRD, Raman spectroscopy and scanning electron microscopy. The results revealed a fast consumption of the precursor and the formation of CuInSebelow 340 °C. Binary secondary phases were not observed at any temperature.
Keywords: Low-temperature; Copper indium gallium diselenide; Chalcopyrite; Nanoparticulate precursors; In-situ X-ray diffraction; Bimetallic nanoparticles

Lubricant-Infused Nanoparticulate Coatings Assembled by Layer-by-Layer Deposition - Vogel, Nicolas; et al. (Advanced Functional Materials, 2014)
Omniphobic coatings are designed to repel a wide range of liquids without leaving stains on the surface. A practical coating should exhibit stable repellency, show no interference with color or transparency of the underlying substrate and, ideally, be deposited in a simple process on arbitrarily shaped surfaces. We use layer-by-layer (LbL) deposition of negatively charged silica nanoparticles and positively charged polyelectrolytes to create nanoscale surface structures that are further surface-functionalized with fluorinated silanes and infiltrated with fluorinated oil, forming a smooth, highly repellent coating on surfaces of different materials and shapes. We show that four or more LbL cycles introduce sufficient surface roughness to effectively immobilize the lubricant into the nanoporous coating and provide a stable liquid interface that repels water, low-surface-tension liquids and complex fluids. The absence of hierarchical structures and the small size of the silica nanoparticles enables complete transparency of the coating, with light transmittance exceeding that of normal glass. The coating is mechanically robust, maintains its repellency after exposure to continuous flow for several days and prevents adsorption of streptavidin as a model protein. The LbL process is conceptually simple, of low cost, environmentally benign, scalable, automatable and therefore may present an efficient synthetic route to non-fouling materials.
Keywords: colloids; layer-by-layer; nanostructures; wetting; omniphobicity

Lubrication of Individual Microcontacts by a Self-Assembled Alkyl Phosphonic Acid Monolayer on α-Al2O3(0001) - Paul, Jonas; Meltzer, Christian; Braunschweig, Björn; Peukert, Wolfgang (Langmuir, 2016)
We report on the tribological behavior of a self-assembled alkyl phosphonic acid monolayer on the microscale using the colloidal probe technique. Friction-load data and adhesion forces were measured with borosilicate glass particles on uncoated and octadecylphosphonic acid (ODPA) coated α-AlO(0001) surfaces. A significant decrease in friction force was observed after surface coating, while the adhesion force was only moderately reduced. We assume the lubrication effect of the ODPA self-assembled monolayer (SAM) to be close to the maximum obtainable of alkyl phosphonic acids in the studied system due to the high molecular order which was confirmed by vibrational sum-frequency generation. At small loads, a nonlinear dependence of friction force to load was maintained after surface coating. However, a shift from a contact behavior well described by the DMT model toward the JKR model occurred that is possibly related to the altered elastic properties of the coated surface. With increasing load, a linear friction-load behavior was observed on the coated samples. Molecular plowing and adhesive interactions were identified as responsible mechanisms. In all friction experiments, we could not detect any wear neither of the colloidal probes nor at the surfaces of uncoated and coated samples. This proves the high wear resistivity of the studied ODPA SAM.

Luminescent down-shifting layers with Eu2+ and Eu3+ doped strontium compound particles for photovoltaics - Solodovnyk, Anastasiia; Hollmann, Andre; Osvet, Andres; Forberich, Karen; Stern, Edda; Batentschuk, Miroslaw; Klupp Taylor, Robin; Brabec, Christoph (Next Generation Technologies for Solar Energy Conversion V, 2014)
In this contribution we discuss luminescent down-shifting (LDS) systems consisting of a polymer matrix filled with phosphor particles. It is an elegant approach to make a use of potentially destructive or otherwise wasted high energy photons and diminish charge carrier losses caused by thermalization in photovoltaics. Sub-micron and micron sized particles of strontium aluminate doped with Eu2+ and strontium carbonate doped with Eu3+ ions are chosen for the application due to their suitable absorption in UV spectral region. These particles exhibit strong luminescence in the visible range between 520 and 650 nm. The systems are carefully designed to meet critical optical requirements such as high transparency in the visible spectrum as well as sufficient absorption of UV light. They are coated on quartz glass substrates (20 x 20 x 1 mm) and can be easily laminated to different kinds of solar cells without any modification to well-established device fabrication processes. Optical characterization further confirms that particles of a few microns in size generate strong light scattering in layers due to the sizes slightly larger than visible light wavelengths. Dried thick layers of 20 to 100 μm are tested with CIGS and organic cells. The concept of light conversion is experimentally proven. However, optical losses cause a reduction in the overall performance of the tested devices. Possible ways to bring down the amount of light scattering and, thus, to increase optical transmission for the studied system are also addressed, and are a subject of future research.
Keywords: Light absorption; Light scattering; Luminescent down-shifting; Phosphor particles; Polymer matrix; Solar cell; Solution processed layers

Magic number colloidal clusters as minimum free energy structures - Wang, Junwei; Mbah Chrameh, Fru; Przybilla, Thomas; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Engel, Michael; Vogel, Nicolas (Nature Communications, 2018)
Clusters in systems as diverse as metal atoms, virus proteins, noble gases, and nucleons have properties that depend sensitively on the number of constituent particles. Certain numbers are termed ‘magic’ because they grant the system with closed shells and exceptional stability. To this point, magic number clusters have been exclusively found with attractive interactions as present between atoms. Here we show that magic number clusters exist in a confined soft matter system with negligible interactions. Colloidal particles in an emulsion droplet spontaneously organize into a series of clusters with precisely defined shell structures. Crucially, free energy calculations demonstrate that colloidal clusters with magic numbers possess higher thermodynamic stability than those off magic numbers. A complex kinetic pathway is responsible for the efficiency of this system in finding its minimum free energy configuration. Targeting similar magic number states is a strategy towards unique configurations in finite self-organizing systems across the scale

Magnéli Phases Doped with Pt for Photocatalytic Hydrogen Evolution - Wierzbicka, Ewa; Domaschke, Maximilian; Denisov, Nikita; Fehn, Dominik; Hwang, Imgon; Kaufmann, Marlena; Kunstmann, Babette; Schmidt, Jochen; Meyer, Karsten; Peukert, Wolfgang; Schmuki, Patrik (ACS Applied Energy Materials, 2019)
Defined TiOx suboxides (Magnéli phases) have rarely been investigated in photocatalysis. In the current work we describe a one-step synthesis of Magnéli-containing mixed phase nanoparticles that carry directly integrated minute amounts with a few hundred ppm of Pt. Nanoparticles can act as highly effective photocatalysts, e.g., mixed phase particles of 32% anatase, 11% rutile, and 57% Magnéli phases loaded with 290 ppm of Pt which provide a 50-100 times higher H2 evolution than plain anatase loaded with a similar amount of Pt. This high photocatalytic efficiency is ascribed to a multijunction of various Magnéli titania species and Pt.
CRIS-Team Scopus Importer:2019-12-20
Keywords: H; Magnéli phase; multiphase titania; photocatalysis; Pt cocatalyst

Magneli-Phases in Anatase Strongly Promote Cocatalyst-Free Photocatalytic Hydrogen Evolution - Domaschke, Maximilian; Zhou, Xuemei; Wergen, Lukas; Romeis, Stefan; Miehlich, Matthias; Meyer, Karsten; Peukert, Wolfgang; Schmuki, Patrik (ACS Catalysis, 2019)
Magneli phases of titanium dioxide (such as Ti4O7, Ti5O9, etc.) provide electronic properties, namely, a stable metallic behavior at room temperature. In this manuscript, we demonstrate that nanoscopic Magneli phases, formed intrinsically in anatase during a thermal aerosol synthesis, can enable significant photocatalytic H-2 generation-this without the use of any extrinsic cocatalyst in anatase. Under optimized conditions, mixed-phase particles of 30% anatase, 25% Ti4O7, and 20% Ti5O9 are obtained that can provide, under solar light, direct photocatalytic H-2 evolution at a rate of 145 mu mol h(-1) g(-1). These anatase particles contain 5-10 nm size intergrown phases of Ti4O7 and Ti5O9. Key is the metallic band of Ti4O7 that induces a particle internal charge separation and transfer cascade with suitable energetics and favorable dimensions that are highly effective for H-2 generation.
CRIS-Team WoS Importer:2019-04-23

Magnetic in situ determination of surface coordination motifs by utilizing the degree of particle agglomeration - Wolf, Andreas; Zink, Andreas; Stiegler, Lisa; Branscheid, Robert; Apeleo Zubiri, Benjamin; Müssig, Stephan; Peukert, Wolfgang; Walter, Johannes; Spiecker, Erdmann; Mandel, Karl (Journal of Colloid and Interface Science, 2023)
Most analytical techniques used to study the surface chemical properties of superparamagnetic iron oxide nanoparticles (SPIONs) are barely suitable for in situ investigations in liquids, where SPIONs are mostly applied for hyperthermia therapy, diagnostic biosensing, magnetic particle imaging or water purification. Magnetic particle spectroscopy (MPS) can resolve changes in magnetic interactions of SPIONs within seconds at ambient conditions. Herein, we show that by adding mono- and divalent cations to citric acid capped SPIONs, the degree of agglomeration can be utilized to study the selectivity of cations towards surface coordination motifs via MPS. A favored chelate agent, like ethylenediaminetetraacetic acid (EDTA) for divalent cations, removes cations from coordination sites on the SPION surface and causes redispersion of agglomerates. The magnetic determination thereof represents what we call a “magnetically indicated complexometric titration”. The relevance of agglomerate sizes for the MPS signal response is studied on a model system of SPIONs and the surfactant cetrimonium bromide (CTAB). Analytical ultracentrifugation (AUC) and cryogenic <a href="https://www.sciencedirect.com/topics/chemistry/transmission-electron-microscopy" title="Learn more about transmission electron microscopy from ScienceDirect's AI-generated Topic Pages">transmission electron microscopy (cryo-TEM) reveal that large micron-sized agglomerates are required to significantly change the MPS signal response. With this work, a fast and easy-to-use characterization method to determine surface coordination motifs of magnetic nanoparticles in optically dense media is demonstrated.
Keywords: Superparamagnetic iron oxide nanoparticles (SPIONs); Magnetic particle spectroscopy (MPS); Agglomeration; Colloidal surface chemistry; Cation coordination

Magnetic polyamide 11 powder for the powder bed fusion process by liquid-liquid phase separation and crystallization - Tischer, Florentin; Cholewa, Simon; Groppe, Philipp; Granath, Tim; Düsenberg, Björn; Mandel, Karl; Drummer, Dietmar; Bück, Andreas; Peukert, Wolfgang; Schmidt, Jochen (Additive Manufacturing, 2024)
Herein, we demonstrate the preparation of magnetic polyamide 11 feedstock powders for powder bed fusion (PBF) using liquid-liquid phase separation and crystallization. By adding magnetic nanomaterials during the precipitation process, the particulate additive is incorporated into the polymer matrix. This enables the production of filled systems at single particle level, which is advantageous in terms of the adjustable magnetic strength and homogeneity of the powder. Thermogravimetric analysis is used to determine the additive content and onset temperature of decomposition of composite powders, where additive-enhancement of PA11 powders with magnetic iron oxide nanoparticles showed a positive influence on the thermal stability of the feedstock. Successive analysis of particle size distribution, shape, colour, crystal structure, magnetic properties and thermal properties of the composite powders are carried out and their properties are discussed with respect to the PBF process. A decrease in particle size, width of the thermal process window and isothermal crystallization time can be attributed to the nucleating effect of the magnetic additive. The PBF processability of the composite feedstock is demonstrated by the production of magnetic tensile bar specimens from additive-enhanced PA11 powders with 1 wt.-% magnetic iron oxide.
CRIS-Team Scopus Importer:2024-06-21
Keywords: Magnets; Nanocomposites; Polymer precipitation; Powder bed fusion; Powder characterization

Magnetic polymer/nickel hybrid nanoparticles via miniemulsion polymerization - Vogel, Nicolas; et al. (Macromolecular Chemistry and Physics, 2013)
Keywords: miniemulsion polymerization; nanoencapsulation; nickel nanoparticles; poly(methyl methacrylate); polystyrene

Magnetizing Polymer Particles with a Solvent-Free Single Stage Process Using Superparamagnetic Iron Oxide Nanoparticles (SPION)s - Düsenberg, Björn; Groppe, Philipp; Müssig, Stephan; Schmidt, Jochen; Bück, Andreas (Polymers, 2022)
Magnetic polymer composites are used in a variety of applications in many industries. Their production methods are usually time-consuming and solvent-intensive as they are performed in liquid phase processes, such as emulsion polymerization or precipitation. In this work, a quick, easy, and solvent-free method is presented to coat polymer particles with a discrete, non-coherent coating of superparamagnetic nanoparticles. The results of the dry coating process are evaluated optically, by means of scanning electron microscopy (SEM), via powder X-ray diffraction and thermally by means of differential scanning calorimetry, before finally demonstrating the effectiveness of dry coating by means of a vibrating sample magnetometer<br

Manufacturing and Application of PA11-Glass Fiber Composite Particles for Selective Laser Sintering - Dechet, Maximilian; Lanzl, Lydia; Werner, Yannick; Drummer, Dietmar; Bück, Andreas; Peukert, Wolfgang; Schmidt, Jochen (Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium 2019, 2019)

Manufacturing of nanoparticle-filled PA11 composite particles for selective laser sintering - Dechet, Maximilian; Lanzl, Lydia; Wilden, Alisa; Sattes, Maria-Melanie; Drummer, Dietmar; Peukert, Wolfgang; Schmidt, Jochen (Proceedings of the 30th Annual International Solid Freeform Fabrication Symposium 2019, 2019)

Mass transport in a partially filled horizontal drum: Modelling and experiments - Tada, Érika Fernanda Rezendes; Bück, Andreas; Tsotsas, Evangelos; Thoméo, João Cláudio (Chemical Engineering Science, 2020)
This work presents a one-phase two-dimensional model describing the mass transport in an isothermal horizontal drum partially filled with silica beads and sugar cane bagasse (SCB), with air flowing in parallel to the bed surface, aiming further applications to solid-state cultivation processes (SSC). The effective diffusivities (Deff) of silica and SCB beds were experimentally determined, as well the equilibrium moisture content of the solids. Deff was of 1.67 10−9 m2/s for the silica bed and 29.2 10−9 m2/s for SCB. Classical correlations were applied to estimate the theoretical effective diffusivity in a bed of spherical (silica beads) and cylindrical (SCB) particles. Experiments were carried out in a still horizontal drum with filling degree 0.5 using low and high air flow rates and good agreement was noted between experimental and simulated results. The results obtained will be of help to model SSC processes in horizontal drums in a more realistic basis.
CRIS-Team Scopus Importer:2020-01-03
Keywords: Effective diffusivity; Horizontal drum; Mass transfer; One-phase model; Sugar cane bagasse

Material properties in fine grinding - Peukert, Wolfgang (European Congress on Comminution, 2002)
The impact of material properties in grinding processes is twofold: <dl class="listitem" id="list_"> • the objective of the comminution process is the production of well-defined product properties, • particles' transport to the stressing zone and particles' reaction to applied stresses depend on their inherent mechanical material properties. </dl> In order to understand the influence of material properties at various length scales, we draw a multiscale picture of comminution. At the most detailed level MD simulations may open insights into the otherwise not accessible zone directly at the crack tip. In continuum approaches, the energy flux from the elastically stressed specimen and the stress distribution around the crack can be modelled. Breakage probability obtained from particle stressing experiments or inversion of milling models can be described by a single master curve comprising two new material parameters. These results are used in mill models by clearly separating machine and material functions. In wet grinding, additional material parameters reflecting the particle–particle interactions are introduced, which control suspension rheology and particle stability. The paper concludes with some remarks on product engineering, i.e. concepts on how to optimise product quality.
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.materi
Keywords: comminution; material; properties; grinding

Material properties in fine grinding - Peukert, Wolfgang (International Journal of Mineral Processing, 2004)
The impact of material properties in grinding processes is twofold:the objective of the comminution process is the production of well-defined product properties,particles' transport to the stressing zone and particles' reaction to applied stresses depend on their inherent mechanical material properties.In order to understand the influence of material properties at various length scales, we draw a multiscale picture of comminution. At the most detailed level MD simulations may open insights into the otherwise not accessible zone directly at the crack tip. In continuum approaches, the energy flux from the elastically stressed specimen and the stress distribution around the crack can be modelled. Breakage probability obtained from particle stressing experiments or inversion of milling models can be described by a single master curve comprising two new material parameters. These results are used in mill models by clearly separating machine and material functions. In wet grinding, additional material parameter reflecting the particle-particle interactions are introduced, which control suspension rheology and particle stability. The paper concludes with some remarks on product engineering, i.e. concepts on how to optimise product quality. (C) 2004 Elsevier B.V All rights reserved.
Keywords: material properties; grinding; comminution

Materials with Hierarchical Porosity Enhance the Stability of Infused Ionic Liquid Films - Galvan, Yaraset; Bauernfeind, Johannes; Wolf, Patrick; Zarraga, Ramon; Haumann, Marco; Vogel, Nicolas (ACS Omega, 2021)
Defined surface functionalities can control the properties of a material. The layer-by-layer method is an experimentally simple yet very versatile method to coat a surface with nanoscale precision. The method is widely used to either control the chemical properties of the surface via the introduction of functional moieties bound to the polymer or create nanoscale surface topographies if one polymeric species is replaced by a colloidal dispersion. Such roughness can enhance the stability of a liquid film on top of the surface by capillary adhesion. Here, we investigate whether a similar effect allows an increased retention of liquid films within a porous surface and thus potentially increases the stability of ionic liquid films infused within a porous matrix in the supported ionic liquid-phase catalysis. The complex geometry of the porous material, long diffusion pathways, and small sizes of necks connecting individual pores all contribute to difficulties to reliably coat the required porous materials. We optimize the coating process to ensure uniform surface functionalization via two steps. Diffusion limitations are overcome by force-wetting the pores, which transports the functional species convectively into the materials. Electrostatic repulsion, which can limit pore accessibility, is mitigated by the addition of electrolytes to screen charges. We introduce nanoscale topography in microscale porous SiC monoliths to enhance the retention of an ionic liquid film. We use gamma-Al2O3 to coat monoliths and test the retention of 1-butyl-2,3-dimethylimidazolium chloride under exposure to a continuous gas stream, a setup commonly used in the water-gas shift reaction. Our study showcases that a hierarchical topography can improve the stability of impregnated ionic liquid films, with a potential advantage of improved supported ionic liquid-phase catalysis.
CRIS-Team WoS Importer:2021-09-03

Measurement of length distribution of beta-lactoglobulin fibrils by multiwavelength analytical ultracentrifugation - Uttinger, Maximilian; Heyn, Timon R.; Jandt, Uwe; Wawra, Simon; Winzer, Bettina; Keppler, Julia K.; Peukert, Wolfgang (European Biophysics Journal, 2020)
The whey protein beta-lactoglobulin is the building block of amyloid fibrils which exhibit a great potential in various applications. These include stabilization of gels or emulsions. During biotechnological processing, high shear forces lead to fragmentation of fibrils and therefore to smaller fibril lengths. To provide insight into such processes, pure straight amyloid fibril dispersions (prepared at pH 2) were produced and sheared using the rotor stator setup of an Ultra Turrax. In the first part of this work, the sedimentation properties of fragmented amyloid fibrils sheared at different stress levels were analyzed with mulitwavelength analytical ultracentrifugation (AUC). Sedimentation data analysis was carried out with the boundary condition that fragmented fibrils were of cylindrical shape, for which frictional properties are known. These results were compared with complementary atomic force microscopy (AFM) measurements. We demonstrate how the sedimentation coefficient distribution from AUC experiments is influenced by the underlying length and diameter distribution of amyloid fibrils. In the second part of this work, we show how to correlate the fibril size reduction kinetics with the applied rotor revolution and the resulting energy density, respectively, using modal values of the sedimentation coefficients obtained from AUC. Remarkably, the determined scaling laws for the size reduction are in agreement with the results for other material systems, such as emulsification processes or the size reduction of graphene oxide sheets.
CRIS-Team Scopus Importer:2020-02-11
Keywords: Amyloid fibrils; Analytical ultracentrifugation; Atomic force microscopy; Beta-lactoglobulin; Sedimentation analysis

Measurement of Solids Velocities in a Co-Current Gas/Solids Flow with a Laser-Doppler-Anemometer and a Capacitance Probe System - Wirth, Karl-Ernst; Richtberg, Martin; Lehner, Peter (Circulating fluidized bed technology VI : proceedings of the 6th International Conference on Circulating Fluidized Beds, 1999)
UnivIS-Import:2015-04-20:Pub.1999.tech.ITC.mechve.measur_53
Keywords: riser; anemometry; laser; fluidized; bed

Measurements of Solid Concentration in a Downward Vertical Gas-Solid Flow - Wirth, Karl-Ernst; Schiewe, Thilo; Molerus, Otto; Sharma, Ashwani; Cheng, J.; Tuzla, K. (Aiche Journal, 1999)
New results from experiments performed in a 15-cm-diameter downflow fast-fluidized bed are presented. Tests were conducted at room temperature and near atmospheric pressure, with 125- μm glass beads. Superficial gas velocities range from 0 to 6.6 m/s. Two different measurement techniques- gamma-absorption tomography and capacitance sensing-were applied to the gas- solids flow in the downer tube. The average local solid fractions from both measurement techniques are compared for various operating conditions of the gas-solid flow. In general, good agreement was obtained between the solid concentration measurements from both measurement techniques. It is demonstrated that combined use of both measurement techniques offers the best chance to get time-average information about the concentration distribution over the whole cross section.
UnivIS-Import:2015-03-05:Pub.1999.tech.ITC.mechve.measur
Keywords: measurements; fluidization; solids

Mechanical activation of trans-stilbene during wet grinding - Konnerth, Christoph-Günther; Damm, Cornelia; Schmidt, Jochen; Peukert, Wolfgang (Advanced Powder Technology, 2014)
The influence of process temperature on product particle size and solubility has been studied for wet grinding of trans-stilbene in ethanol. A positive effect of lowering the process temperature with respect to minimum product particle size was observed. Remarkably, the smallest product particle sizes x < 1 μm were found for the lowest process temperature (251 K) at short process times (< 30 min) and moderate stressing conditions. In contrast, for the same stressing conditions at room temperature (293 K) particles of approximate size x ≈ 8 μm are obtained. The product particle size is rather determined by the (temperature- and solvent-dependent) solid-liquid equilibrium, i.e. dissolution and precipitation phenomena, than by pure mechanical fracture. An increased solubility of stressed trans-stilbene with respect to the equilibrium solubility of the solid has been observed. By means of H NMR spectroscopy and thermodynamic considerations it is shown that the solubility increase is neither due to an isomerisation of the solid nor due to size effects. In fact, mechanical activation leads to an increase in solubility of the stressed solid which was clearly proven by means of solubility studies at different temperatures. The van't Hoff enthalpy of dissolution of the stressed solid decreased remarkably in comparison to the enthalpy of the non-stressed solid as shown by evaluation of van't Hoff plots.
Keywords: Enhanced solubility; Enthalpy of dissolution; Organic crystal; trans-Stilbene; Wet grinding

Mechanically induced phase transformation of zinc sulfide - Damm, Cornelia; Armstrong, Patrick; Roßkopf, Christian; Romeis, Stefan; Peukert, Wolfgang (Particuology, 2015)
Molecular dynamics (MD) simulations of the consecutive compression-decompression cycles of hexagonal zinc sulfide (wurtzite) nanoparticles predict an irreversible phase transformation to the cubic polymorph. The phase transformation commences at the contact area between the particle and the indenter and proceeds with the number of compression cycles. Dislocations are visible for a particle size above 5 nm. Results from wet grinding and dry powder compression experiments on a commercial wurtzite pigment agree qualitatively with MD simulation predictions. X-ray diffraction patterns reveal that the amount of cubic polymorph in the compressed samples increases with pressure applied to the powder. In comparison with powder compression, wet milling leads to a more pronounced phase transformation. This occurs because the particles are exposed to a large number of stress events by collision with the grinding media, which leads to the formation of defects and new surface crystallites by particle fracture. According to the MD simulations, phase transformation is expected to occur preferentially in surface crystallites because they experience the highest mechanical load. Because of the phase transformation, the wet ground and compressed samples exhibit a lower photoluminescence intensity than the feed material. In comparison with powder compression, milling reduces the photoluminescence intensity more substantially. This occurs because a higher defect concentration is formed. The defects contribute to the phase transformation and photoluminescence quenching.
Keywords: Molecular dynamics simulation; Polymorph transformation; Powder compression; Wet milling; Zinc sulfide

Mechanical particle properties - design, characterization and application - Romeis, Stefan; Peukert, Wolfgang; Paul, Jonas (International Conference for Conveying and Handling of Particulate Solids (CHoPS2015), 2015)
The (nano-)mechanics of particles across all length scales down to the nanoscale are highly relevant for many applications including adhesion, friction, powder flow, comminution and tribology. Nanomechanical elastic and inelastic particle properties have been measured systematically in a novel nanoindentation device installed within a scanning electron microscope to obtain simultaneously forcedisplacement information and optical images of deformed and broken particles. Quantitative data of intrinsic particle properties (and their respective distributions) are measured for oxide, metal and polymer particles. We discuss structure - property functions of particles in a quantitative way for selected applications, e.g. the production of bioactive glass and novel polymer particles in additive manufacturing.
Keywords: nano; mechanic; particle; powder; flow

Mechanical production and stabilisation of submicron particles in stirred ball media mills - Peukert, Wolfgang; Mende, Stefan; Stenger, Frank; Schwedes, Jörg (Powder Technology, 2003)
A joint research project between the Technical University of Braunschweig and the Technical University of München investigates the possibilities for the production of stable product suspensions in a particle size range smaller than 100 nm. This paper shows the experimental setup which allows the measurement of the most important electrochemical properties and the analysis of the particle size distribution of the product suspension as well as an adjustment of the pH value for stabilization during the comminution process. Results for comminution of fused corundum with different grinding media materials and grinding media sizes are shown. In addition, results showing the influence of the electrostatic stabilization on the grinding progress are presented. Further, the rheology of the product suspension is examined depending on grinding progress and suspension stabilit
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.mechan
Keywords: Ultrafine grinding; Submicron particles; Stirred media mill; ζ potential; Electrostatic stabilization; Fused corundum

Mechanical production and stabilisation of submicron particles in stirred ball media mills - Peukert, Wolfgang; Mende, Stefan; Stenger, Frank; Schwedes, Jörg (European Congress on Comminution, 2002)
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.mechan_8
Keywords: stabilization; ball; mill

Mechanical Properties of Three-Dimensional Laser Sintered Bone Substitutes of Polyetheretherketone - Pohle, D.; Rechtenwald, T.; Damm, Cornelia (Proceedings of 20th European Conference on Biomaterials, Nantes, France, 2006)
LFT Import::2019-08-05 (1285)

Mechanical Stability of Liquid-Infused Surfaces Based on Mussel-Inspired Polydopamine Chemistry - Chiera, Salvatore; Ghetina, Melissa; Zimmermann, Thomas; Wintzheimer, Susanne; Stauch, Claudia; Loebmann, Peer; Mandel, Karl; Vogel, Nicolas (Macromolecular Materials and Engineering, 2023)
Liquid-infused surfaces exhibit remarkable repellency properties toward water, oils, and complex fluids and are widely applied to maintain clean, operational, and high-performing surfaces in various fields, from the biomedical sector to marine infrastructure. Polydopamine (PDA) forms an ideal base layer for the development of such coatings as it adheres to virtually any substrate and can be chemically modified via amino-containing molecules to adjust the surface properties. Here, strategies are explored to increase the mechanical stability of such coatings by i) incorporating imidazole during film formation to increase crosslinking, and ii) formation of a composite consisting of the organic PDA and an inorganic siliceous porous coating by infiltration of a preformed porous silica layer with PDA. Both strategies exhibit improved resistance to tangential shear assessed by a sandpaper abrasion test and to dynamic impact assessed by a sand trickle test. These improved mechanical properties are successfully transferred to liquid-infused surfaces created from such modified PDA base layers. The most durable coatings retain efficient liquid repellency after 25 abrasion cycles, indicating improved resilience in real-world application
Keywords: liquid-infused surfaces; mechanical resistance; coatings; polydopamine; wetting

Mechanics of colloidal supraparticles under compression - Wang, Junwei; Schwenger, Jan; Feldner, Patrick; Ströbel, Andreas; Herre, Patrick; Romeis, Stefan; Peukert, Wolfgang; Merle, Benoit; Vogel, Nicolas (Science Advances, 2021)
Colloidal supraparticles are finite, spherical assemblies of many primary particles. To take advantage of their emergent functionalities, such supraparticles must retain their structural integrity. Here, we investigate their size-dependent mechanical properties via nanoindentation. We find that the deformation resistance inversely scales with the primary particle diameter, while the work of deformation is dependent on the supraparticle diameter. We adopt the Griffith theory to such particulate systems to provide a predictive scaling to relate the fracture stress to the geometry of supraparticles. The interplay between primary particle material and cohesive interparticle forces dictates the mechanical properties of supraparticles. We find that enhanced stability, associated with ductile fracture, can be achieved if supraparticles are engineered to dissipate more energy via deformation of primary particles than breaking of interparticle bonds. Our work provides a coherent framework to analyze, predict, and design the mechanical properties of colloidal supraparticle

Mechanische Erzeugung und Stabilisierung von Nanopartikeln in Rührwerkskugelmühlen - Peukert, Wolfgang; Stenger, Frank; Mende, Stefan; Schwedes, Jörg (Chemie Ingenieur Technik, 2002)
Die   Herstellung   von   Produkten   immer   höherer   Homogenität,   Löslichkeit   oder   Festigkeit  erfordert  oftmals  den  Einsatz  immer  feinerer  Partikeln  als  Rohstoff.  Zur  Herstellung  solcher  Partikelsysteme  kommen  zwei  Methoden  in  Frage.  Bei  der  Kondensationsmethode  entstehen  die  Partikeln  durch  Aggregation  molekular  in  gelöster    flüssiger    oder    gasförmiger    Form    vorliegender    Stoffe.    Vorteil    der    Kondensationsmethode ist die Möglichkeit der Herstellung hochreiner monodisperser sphärischer  Partikelsysteme.  Nachteil  ist  die  in  der  Regel  sehr  geringe  maximale  Produktionsleistung.    Die    Herstellung    feinster    Partikeln    durch    mechanische    Beanspruchung  und  Zerkleinerung  grober  Partikeln  wird  als  Dispersionsmethode  bezeichnet.    Für  eine  solche  Zerkleinerungsaufgabe  müssen  hohe  Energiedichten  zur  Verfügung  gestellt  werden,  wie  sie  z.  B.  in  Rührwerkskugelmühlen  realisiert  werden  können.  Rührwerkskugelmühlen  werden  vorwiegend  naß  betrieben.  Sie  werden  unter  anderem  zur  Zerkleinerung  von  Rohstoffen  für  die  chemische  und  pharmazeutische  Industrie,  die  Keramikindustrie,  die  Mikroelektronikindustrie,  die  Lebensmittelindustrie  sowie  zur  Dispergierung  feiner  Pigmente  in  der  Farben-  und  Lackindustrie eingesetzt. Ein   wesentliches   Problem   bei   der   Naßzerkleinerung   in   Rührwerkskugelmühlen   stellen    die    mit    zunehmender    Mahlgutfeinheit    steigenden    interpartikulären    Wechselwirkungen  dar.  Diese  Wechselwirkungen  beeinflussen  die  Stabilität  der  Mahlgutsuspension gegenüber Koagulation sowie deren rheologische Eigenschaften.  Ohne  zusätzliche  Stabilisierung  der  Produktpartikeln  entsteht  daher  in  vielen  Fällen  ein   Wechselspiel   zwischen   Bruch   und   Reagglomeration,   so   daß   bei   früheren   experimentellen  Untersuchungen  nach  dem  Erreichen  einer  Mahlgutfeinheit  von  ca.  0,5  μm  trotz  weiterer  Erhöhung  des  spezifischen  Energieeintrags  festgestellt  wurde,  daß die gemessene Mahlgutpartikelgröße wieder anstieg, obwohl die nach der BET-Methode gemessene spezifische Oberfläche ebenfalls anstieg.  In einem gemeinsamen DFG-Forschungsprojekt mit dem Lehrstuhl für Feststoff- und Grenzflächenverfahrenstechnik  der  TU  München  wurde  daher  untersucht,  wie  sich  das  Zerkleinerungsverhalten  im  Nanometer-Bereich  im  Vergleich  zur  Zerkleinerung  auf  Partikelgrößen  bis  etwa  1  μm  verändert.  Für  die  Zerkleinerung  im  Nanometer-Bereich  ist  die  Stabilisierung  der  Feststoffpartikeln  in  der  Suspension  zwingend  erforderlich.  Zu  diesem  Zweck  wurden  auftretende  Agglomerationserscheinungen  durch  die  elektrostatische  Stabilisierung  der  Mahlgutsuspension  unterbunden.  Ein  weiteres   Ziel   der   Untersuchungen   war   es,   festzustellen,   wie   die   maximal   in   Rührwerkskugelmühlen      erreichbare      Produktfeinheit      durch      verschiedene       Betriebsparameter beeinflußt wird.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.mechan
Keywords: nanoparticle; comminution; ball; mill

Mechanism of Silver Ion Reduction in Concentrated Solutions of Amphiphilic Invertible Polyesters in Nonpolar Solvent at Room Temperature - Voronov, Andriy; Kohut, Ananiy; Vasylyev, Serhiy; Peukert, Wolfgang (Langmuir, 2008)
Fast formation and efficient stabilization of silver nanoparticles from [Ag(NH3)(2)]OH are achieved in concentrated nonpolar solutions of amphiphilic invertible polyesters based on poly(ethylene oxide) (PEO) and aliphatic dicarboxylic acids. Surface-modified silver nanoparticles able to be dispersed in both a polar and nonpolar medium are developed in the form of a ready-to-use colloidal solution with an enhanced silver concentration. The PEO fragments of polyesters form cavities (also called pseudo-crown ester structures) that can bind metal ions. The reduction of bound metal ions proceeds. via oxidation of polyoxyethylene fragments. No chemical reducing agents are necessary in this approach. The polyesters act simultaneously as an efficient reducing agent and stabilizer. The main focus of the present research is to clarify the chemical mechanism of silver ion reduction in amphiphilic polyester solutions. A one-electron reduction mechanism is proposed to explain the formation of silver nanoparticles. The effect of the poly(ethylene oxide) fragment length and the polyester concentration are explored by examining several amphiphilic polyesters.

Mechanistic insights into silver-gold nanoalloy formation by two-dimensional population balance modeling - Traore, Nabi; Schikarski, Tobias; Cardenas Lopez, Paola Ivonne; Körner, A.; Cardenas Lopez, Paola Ivonne; Hartmann, Lukas; Fritsch, B.; Walter, Johannes; Hutzler, A.; Pflug, Lukas; Peukert, Wolfgang (Chemical Engineering Journal, 2024)
The large-scale synthesis of nanoparticles (NPs) with defined properties requires detailed understanding of the underlying formation mechanisms and kinetics. The formation mechanisms of bimetallic NPs are still not sufficiently understood due to the complex reaction chemistry, which makes the control of the supersaturation as the thermodynamic driving force challenging. Particle size, chemical composition, and the distribution of the elements within the particles change dynamically during particle formation. In this work, we propose a mechanism for the formation of bimetallic silver-gold alloy NPs via a green liquid-phase co-reduction synthesis and develop a two-dimensional population balance model to quantitatively describe the evolution of particle size distribution, composition, and optical properties. We shed light on the complex multi-stage formation mechanism of a highly relevant bimetallic NP system, lay the foundation for tailoring the process conditions to achieve targeted optical particle properties and unravel predictive property-process relationships.
CRIS-Team Scopus Importer:2024-02-23
Keywords: Alloy Nanoparticle; Formation Mechanism; Gold Nanoparticle; Nanoparticle Synthesis; Population Balance Equation; Silver Nanoparticle

Mechanochemical aspects in wet stirred media milling - Romeis, Stefan; Schmidt, Jochen; Peukert, Wolfgang (International Journal of Mineral Processing, 2016)
Wet comminution in stirred media mills is a frequently applied fully scalable top-down method towards the production of micron- and submicron particles. Despite the vast field of mechanochemistry which encompasses an increase in reactivity due to the effect of mechanical energy input, there is still no clear picture of the involved mechanisms. In ultra-fine wet grinding the situation is further complicated due to the presence of the solvent: reactions of the stressed solid with the surrounding liquid phase can occur. In this paper several aspects of mechanochemistry occurring in stirred media mills are outlined through suitable experiments. Main focus lies on the comprehensive product characterization and on the role of the liquid phase. It is shown that the liquid phase influences product properties like particle size, porosity, particle shape, structure, chemical composition and the molecular termination of the surface. An increase in the reactivity of ground solids is manifested by a significant increase in dissolution in the aqueous phase during processing in water. Altogether, the liquid dispersion medium which can act as solvent is thus introduced as a new process parameter in stirred media milling and offers new prospects for innovative product design by top-down approaches.
Keywords: Amorphization; Glass; Liquid phase analysis; Mechanochemistry; Quartz; Reactivity; Solubility; Stirred media mills; Titania; Wet comminution

Mechano-chemical changes of nano sized α-Al2O3 during wet dispersion in stirred ball mills - Peukert, Wolfgang; Stenger, Frank; Götzinger, Martin; Jakob, Peter (Particle & Particle Systems Characterization, 2004)
The mechano-chemical changes in synthetic α-AlO during wet dispersion in a stirred ball mill, are studied. It is shown that a second phase is generated which can be identified as an aluminum hydroxide (Bayerite) by use of dynamic scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetry (TG), Fourier transformed infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). The amount of the Bayerite phase produced increases with milling time. A comparison of the evaluated amounts from TG- and DSC-measurements are in reasonable agreement. Furthermore, the measured BET surface area shows a strong dependence on the temperature of sample preparation. Depending on the temperature, the bayerite phase is seen to convert to the α-phase again and also forms meso- and possibly micro-pores, leading to a high BET surface area. In this paper, we highlight the necessity for using different methods to characterize the dispersion process, and for a correct interpretation of the measurement results.
Keywords: α-alumina; Bayerite; Mechano-chemical characterization; Wet dispersing

Mechanochemically induced sulfur doping in ZnO via oxygen vacancy formation - Daiko, Yusuke; Schmidt, Jochen; Kawamura, Go; Romeis, Stefan; Segets, Doris; Iwamoto, Y.; Peukert, Wolfgang (Physical Chemistry Chemical Physics, 2017)
Surface defects of ZnO nanoparticles were induced via mechanical stressing using a Turbula shaker mixer and a planetary ball mill, and the possibilities for surface modification and functionalization of the ZnO nanoparticles were exemplified by sulfur doping of activated ZnO. Raman spectroscopy reveals that the formation of oxygen vacancies (VO) does not only occur under high stressing conditions in a planetary ball mill but even upon rather 'mild stressing' in the shaker mixer. The temporal evolution of the vacancy concentration in ZnO stressed under different conditions can be described by a model that accounts for stress number and vacancy diffusion with diffusion coefficients of VO of 3.7 × 10-21 m2 s-1 and 2.4 × 10-20 m2 s-1 for stressing in the shaker and the planetary ball mill, respectively. The thickness of the VO layer was estimated to be about 1 nm. Thiourea was mixed with defective ZnO particles, and then heated at various temperatures for sulfur-doping. A linear relationship between the amount of induced VO and the level of sulfur doping was found. Remarkably, mechanical activation is indispensable in order to control the level of sulfur doping quantitatively. High-angle annular dark field scanning transmission electron microscopy (HAADF STEM) observations with energy dispersive X-ray spectroscopy (EDX) analysis clearly revealed that the doped sulfur atoms are concentrated at the particle surface. Thus, ZnO (core)/ZnS (shell) structures are obtained easily via mechanochemical activation and subsequent thermal treatment.

Mechanochemical modification of silica with poly(1-vinyl-2-pyrrolidone) by grinding in a stirred media mill - Voronov, Andriy; Kohut, Ananiy; Synytska, A.; Peukert, Wolfgang (Journal of Applied Polymer Science, 2007)
The polymerization of 1-vinyl-2-pyrrolidone (VP) mechanochemically initiated by grinding silica was investigated in a wet stirred media mill. The polymerization itself proceeds from the silica grinding without any additional initiator. We have found that the amount of grafted polymer increases with an increase in total ground silica surface. The suspension of polymer-modified silica nanoparticles showed high colloidal stability in water because of the appearance of grafted hydrophilic PVP on the surface during the reactive grinding. Because the nanoparticles SiO2-graft-PVP are bio-compatible, the developed polymer nanocomposite material can be of particular interest for the performance of membranes and for the fabrication of biocompatible hydrogels with enhanced mechanical properties and porosity. (c) 2007 Wiley Periodicals, Inc.
Keywords: graft hydrophilic polymers; nanoparticles; reactive grinding

Mechano-chemical radical formation and polymerization initiation during wet grinding of alumina - Damm, Cornelia; Peukert, Wolfgang (Journal of Colloid and Interface Science, 2011)
The formation of free radicals during wet grinding of alumina in a stirred media mill was studied by using the test radical 2,2-diphenyl-1-picrylhydracyl (DPPH). The kinetics of mechano-chemical radical formation follows a zeroth-order rate law. Particle breakage as well as mechanical activation of the surface of the alumina particles contributes to the radical formation. The rate constants of the radical formation due to mechanical activation of the particle surface k and due to particle breakage k depend on the milling process parameters. The radical formation during wet grinding of alumina was exploited to initiate mechano-chemical polymerization reactions of acrylic acid and acryl amide, respectively. In this way nanoparticles functionalized with polyacrylic acid and polyacryl amide, respectively, are obtained. The influence of the milling process parameters on the kinetics of mechano-chemical radical formation and on the grafted amount of polymer is discussed on the basis of stress energy and number of stress events in the mill. A correlation between the grafted amount of polyacryl amide on the alumina particles and the total radical formation rate was found showing that the concentration of mechano-chemically formed free radicals governs the efficacy of a chemical reaction at activated particle surfaces. © 2011 Elsevier Inc.
Keywords: Alumina; Kinetics; Mechano-chemical polymerization; Radical formation; Stirred media mill

Mesoporous Organosilicas With Large Cage-Like Pores for High Efficiency Immobilization of Enzymes - Zhou, Zhou; Klupp Taylor, Robin; Kullmann, Simon; Bao, Huixin; Hartmann, Martin (Advanced Materials, 2011)
A group of hierarchically ordered PMOs with large cage-like pores are prepared with organosilica units including ethylene, ethenylene, and phenylene-bridged silanes. The structure and hydrophobicity of these materials are shown to offer significant advantages for the physical adsorption of lipase from aqueous media and also markedly enhance its activity.

Mesoporous silica submicron particles (MCM-41) incorporating nanoscale Ag: synthesis, characterization and application as drug delivery coatings - Boccardi, Elena; Liverani, Liliana; Beltrán, A. M.; Günther, R.; Schmidt, Jennifer; Peukert, Wolfgang; Boccaccini, Aldo R. (Journal of Porous Materials, 2018)
Keywords: Mesoporous particles; Scaffolds; Drug delivery; Silica; Silver

Metallic nanoparticle-on-mirror: Multiple-band light harvesting and efficient photocurrent generation under visible light irradiation - Tesler, Alexander; Sannomiya, Takumi; Hejazi, Seyedsina; Mohammadi Eslami, Reza; Vogel, Nicolas; Altomare, Marco; Schmuki, Patrik (Nano Energy, 2021)
We present a photoanode concept for photoelectrochemical (PEC) water splitting based on metal nanoparticles (Au, Ag, Cu) deposited on a Ti mirror (NPoM) to photosensitize an intermediate TiO2 layer to induce the harvesting of light with sub-bandgap photon energies. The generation of hot electron-hole pairs in metallic nanostructures can occur either by intraband excitation, i.e., plasmon electrons, or by the interband transition of the d-band electrons to the unoccupied conduction band states. Our results demonstrate that the underlying Ti mirror significantly amplifies the PEC activity of such NPoM systems in the visible spectral range. We show that the PEC enhancement in the visible spectral range is not limited to the intraband excitations but is affected mainly by the light trapping pathway within the TiO2 layer, i.e. due to a favorable interplay between thin-film interference cavity modes with both intraband and interband excitations. Among tested metals, Cu and Ag NPs demonstrate a 3-fold higher enhancement factor than that of Au NPs, while in both former cases the nature of the excited electrons is different. The experimentally determined internal quantum efficiency demonstrates alternating behavior with wavelength showing higher efficiencies at short wavelengths, which is attributed to the reduced Schottky barrier of the NPoMs at constructive interference maxima.
CRIS-Team Scopus Importer:2021-10-22
Keywords: Fabry-Pérot interference; Interband excitations; Metallic nanoparticles; Photoelectrochemistry; Titanium dioxide; Water splitting

Metal oxide particle networks from powder mixtures: Generation of functional heterojunctions via surface charge induced heteroaggregation - Siedl, Nicolas; Baumann, Stefan O.; Diwald, Oliver (ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, Volume: 246, 2013)

Microflow-based control of near-wall fluctuations for large viscous drag reduction - Jovanovic, Jovan; Srikantharajah, Rubitha; Lienhart, Hermann; Delgado, Antonio; Frohnapfel, Bettina; Jovanović, Djordje (Microfluidics and Nanofluidics, 2011)
The stabilizing effect of microgroove surface morphology on viscous drag reduction was studied experimentally in the inlet region of a plane channel flow. The stabilization is thought to be due to the ability of a microgrooved surface pattern to suppress the velocity fluctuations in the spanwise direction on a restricted portion of the wetted surface, which prevents vorticity development at the wall and consequently across the entire flow field. This smart microflow control strategy, which works successfully only under very particular circumstances, was implemented in a microgroove-modified channel flow in which the front part has a microgrooved surface topology. The results of pressure drop measurements indicate that microgrooved surfaces can effectively stabilize laminar boundary layer development, leading to a significant reduction in the viscous drag. In the rear flat part of the microgroove-modified channel test section, a maximum drag reduction of DR ≃ 35% was measured. This corresponds to an overall drag reduction of DR ≃ 16% at a length Reynolds number of Re x ≃ 10 6: The drag reduction effect persisted in a narrow range of flow velocities and for the reported experimental conditions corresponds to microgroove dimensions between 1.5 and 2.5 viscous length-scales. © Springer-Verlag 2011.
UnivIS-Import:2015-03-09:Pub.2011.tech.ITC.stmmec.microf
Keywords: microflow; drag; control

Microscale investigation of the correlation between microstructure and galvanic corrosion of low alloy steel A508 and its welded 309/308L stainless steel overlayer - Okonkwo, Bright O.; Ming, Hongliang; Zhang, Zhiming; Wang, Jianqiu; Rahimi, Ehsan; Hosseinpour, Saman; Davoodi, Ali (Corrosion Science, 2019)
The microscopic scale correlation between microstructure and galvanic corrosion of low alloy steel-A508 and its welded-309/308L stainless steel overlayer is investigated. Microstructural characterization shows that the welding process induces complexities at HAZ of the base metal. The microstructure of HAZ changes from tempered bainite to a non-uniform mixture of martensite and bainite, depending on the heat flow. This change in the microstructure leads to a heterogeneous corrosion attack on the base metal (anode), while the weld metal (cathode) is protected in a galvanic interaction. The extent and rate of corrosion attacks on the surface constituents are quantified by AFM.
CRIS-Team Scopus Importer:2019-05-07
Keywords: AFM; Inclusion; Interface; Low alloy steel; SEM; Stainless steel

Microstructural characterization of hematite during wet and dry millings using Rietveld and XRD line profile analyses - Peukert, Wolfgang; Pourghahramani, Parviz; Altin, Ergün; Mallembakam, Madhusudhan Rao; Forssberg, Eric (Powder Technology, 2008)
The effects of extended milling in a stirred media mill and a tumbling mill on the structural changes in hematite have been examined using a combination of particle size analysis, BET surface areas, X-ray diffraction (XRD), thermal (TG and DSC) and FTIR measurements. Rietveld's whole profile fitting based on crystal structure refinement and the Warren-Averbach's method of X-ray line profile analysis were applied to monitor the microstructural evolution of the hematite phase. It is found that the BET surface area, X-ray amorphization phase content and XRD line breadths increase over the specific energy input. The use of stirred media mill exhibits larger surface areas, smaller particle sizes, more XRD line broadening and subsequently greater structural distortions compared to the tumbling mill for a given energy input; although the X-ray amorphous phase content remains unaffected by the grinding environments. The maximum X-ray amorphization degree of about 80 and 95% were calculated at a specific energy of 22,400 and 82,000 kJ/kg in the tumbling and stirred media mills respectively. The maximum specific BET surface area in the stirred media and tumbling milling increases to about 72.5 and 6.8 m/g after 82,000 and 22,400 kJ/kg energy consumption respectively. As a result of structural refinement during milling, the surface-weighted crystallite size in ground hematite are 17 and 4 nm after consuming 22,400 and 82,000 kJ/kg in the tumbling and stirred media mills respectively, corresponding to the volume-weighted crystallite size of 17 and 11 nm. For the same energy consumption in the mills, in turn, the root mean square strain, 〈 ε 〉, increases to about 4.4 × 10 and 4.9 × 10. The results of the two applied methods are compared and discussed in details. In addition, thermogravimetric analysis of the wet ground samples reveals that the TG curves represent two weight loss steps. A weight loss is observed around 100 °C in the sample which is attributed to the removal of adsorbed water due to the wet milling operations. A strong weight loss step starting from 100 to 400 °C is attributed to surface/bulk dehydroxilation of iron hydroxides. The weight loss increases with extending of the milling. In contrast, the dry milled samples yield negligible weight losses comparing with the wet ground samples. © 2007 Elsevier B.V. All rights reserved.
Keywords: Iron oxide; Mechanical activation; Structural changes; Wet and dry milling

Microstructural evolution during deformation of tin dioxide nanoparticles in a comminution process - Armstrong, Patrick; Knieke, Catharina; Mackovic, Mirza; Frank, Gerhard; Hartmaier, Alexander; Göken, Mathias; Peukert, Wolfgang; Mackovic, Mirza (Acta Materialia, 2009)
Nanoparticles can be produced by wet grinding in stirred media mills if agglomeration is prevented by stabilization of the particles. Since the fracture mechanisms at the lower nanoscale are not yet understood, we studied the evolution of the microstructure within tin dioxide particles. Electrostatic stabilization allows the formation of tin dioxide with a mean particle size of 25 nm as measured by dynamic light scattering. High-resolution transmission electron microscopy (HRTEM) images show particles well below 10 nm and mean crystallite sizes of 9 nm were obtained from X-ray diffraction by applying the Rietveld refinement method. Additionally, TEM and HRTEM analyses were conducted to gain detailed insight into the microstructural effects governing the grinding process. Microscopy revealed surprisingly rich phenomena including the formation of shear bands, twinning and stacking faults that directly affect the grinding behavior. Interestingly the ceramic nanoparticles showed not only fracture patterns expected from brittle fracture but also many traces of plastic deformation. For comparison the uniaxial compression of particles up to 30 nm in diameter was simulated using molecular dynamics. The simulated particles shared microstructural details with the real samples, most importantly the shear bands which lead to significant plastic deformation. The internal microstructure produced during multiple particle stressing events in the mill and also observed in the simulations is directly linked to the fracture mechanism and the experimentally observed grinding limit. © 2009 Acta Materialia In
UnivIS-Import:2015-03-09:Pub.2009.tech.IW.LM.micros
Keywords: Molecular dynamics simulations; Nanomechanics; Nanostructure; Shear bands; Transmission electron microscopy (TEM)

Microstructure characteristics of non-monodisperse quantum dots: On the potential of transmission electron microscopy combined with X-ray diffraction - Neumann, Stefan; Menter, Christina; Mahmoud, Ahmed Salaheldin Abdelhamid; Segets, Doris; Rafaja, David (Crystengcomm, 2020)
Although the concept of quantum confinement was introduced more than thirty years ago, a wide application of quantum dots is still limited by the fact that monodisperse quantum dots with controlled optoelectronic properties are typically synthesized on a relatively small scale. Larger scale synthesis techniques are usually not able to produce monodisperse nanoparticles yet. In this contribution, we illustrate the capability of the combination of transmission electron microscopy and X-ray diffraction to reveal detailed and scale-bridging information about the complex microstructure of non-monodisperse quantum dots, which is the first step towards further upscaling of the techniques for production of quantum dots with controlled properties. As a model system, CdSe quantum dots synthesized using an automated robotic hot-injection method at different temperatures were chosen. The combined microstructure analytics revealed the size and shape of the CdSe nanocrystals and the kind, density and arrangement of planar defects. The role of the planar defects in the particle coarsening by oriented attachment and the effect of the planar fault arrangement on the phase constitution, on the crystallographic coherence of the counterparts and on the optoelectronic properties are discussed.
CRIS-Team Scopus Importer:2020-06-09

Microstructure formation in dip-coated particulate films - Peukert, Wolfgang; Günther, Lübbe; Goerigk, Günter; Dingenouts, Nico (Journal of Colloid and Interface Science, 2006)
The microstructure-dependence of dip-coated particulate thin films on the stability of an aqueous silica sol used as coating bath is studied. Different stability conditions are adjusted in the sol by changing electrolyte concentration and pH value. Care was taken to avoid pronounced aggregation of the particles before the coating process. The characterization of the stability behavior gives clear evidence of a non-DLVO contribution at low pH values that is attributed to hydration forces. Structural evolution of the particulate network during film formation is studied using a dialysis accumulation procedure. The viscosity of the accumulated sol is measured as a function of shear rate and related to the drying characteristic of the coating process. Atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and N sorption are used to obtain information on the surface and volume structure of the dip-coated films. The structure of coatings is found to distinctly vary with stability parameters. This is attributed to changing interactions during the first drying stage. Finally, the influence of coating structures on the light transmission properties is determined. A comparison between the extinction of the uncoated and the coated substrate revealed a difference of up to ±50% in dependence on the microstructure. © 2005 Elsevier Inc. All rights reserved.
Keywords: Colloidal stability; Dip coating; Film structure; Particles; Pore size distribution; Rheology; Small-angle scattering

Microwave drying of wet clay with intermittent heating - Vorhauer, N.; Tretau, A.; Bück, Andreas; Prat, M. (Drying Technology, 2019)
In this article, we study an alternative process for the conservative drying of wet clay based on combined microwave heating and convective drying. The study is founded on an experimental analysis of the processes that control drying of porous matter in presence of temperature gradients. We show and discuss that process control cannot be reliably based on temperature alone because mass transfer phenomena associated with microwave heating dictate drying kinetics. Essentially, the occurrence of pressure build up and liquid expulsion, dominating mass transfer if microwave heating is uncontrolled or with high power, vitally depend on the moisture content of the clay. As a consequence, the deterioration of clay is problematic if internal evaporation rates are high, thus at the start of drying when also the moisture content is high. Following this, we propose intermittent microwave heating in combination with convective drying periods with the aim to reduce overall drying time (compared to conventional convective drying) and to improve product quality by reduced material shrinkage. Drying experiments indicate that the overall drying time reduction and product quality depend on the frequency and duration of the two subsequent periods of intermittent heating and convective drying. The observations can be explained with the evolution of the pore-scale distribution of liquid and vapor during drying.
CRIS-Team Scopus Importer:2019-05-02
Keywords: clay; Drying; intermittent dielectric heating; microwave

Minimization of catalyst loading on regenerative fuel cell positive electrodes based on Ti felts using atomic layer deposition - Schlicht, Stefanie; Barr, Maissa; Wu, Mingjian; Hoppe, Paula; Spiecker, Erdmann; Peukert, Wolfgang; Bachmann, Julien (ChemElectroChem, 2018)

Minkowski Tensor Shape Analysis of Cellular, Granular and Porous Structures - Peukert, Wolfgang; Schröder-Turk, Gerd; Mickel, Walter; Kapfer, Sebastian; Klatt, Michael; Schaller, Fabian; Hoffmann, Matthias; Kleppmann, Nicola; Inayat, Amer; Armstrong, Patrick; Hug, Daniel; Reichelsdorfer, Martin; et al. (Advanced Materials, 2011)
Predicting physical properties of materials with spatially complex structures is one of the most challenging problems in material science. One key to a better understanding of such materials is the geometric characterization of their spatial structure. Minkowski tensors are tensorial shape indices that allow quantitative characterization of the anisotropy of complex materials and are particularly well suited for developing structure-property relationships for tensor-valued or orientation-dependent physical properties. They are fundamental shape indices, in some sense being the simplest generalization of the concepts of volume, surface and integral curvatures to tensor-valued quantities. Minkowski tensors are based on a solid mathematical foundation provided by integral and stochastic geometry, and are endowed with strong robustness and completeness theorems. The versatile definition of Minkowski tensors applies widely to different types of morphologies, including ordered and disordered structures. Fast linear-time algorithms are available for their computation. This article provides a practical overview of the different uses of Minkowski tensors to extract quantitative physically-relevant spatial structure information from experimental and simulated data, both in 2D and 3D. Applications are presented that quantify (a) alignment of co-polymer films by an electric field imaged by surface force microscopy; (b) local cell anisotropy of spherical bead pack models for granular matter and of closed-cell liquid foam models; (c) surface orientation in open-cell solid foams studied by X-ray tomography; and (d) defect densities and locations in molecular dynamics simulations of crystalline coppe
Keywords: geometric; statistic; spatial; anisotropy; shape; morphology; crystal

Mixed Layers of β-Lactoglobulin and SDS at Air-Water Interfaces with Tunable Intermolecular Interactions - Engelhardt, Kathrin; Weichsel, Ulrike; Kraft, Elena; Segets, Doris; Peukert, Wolfgang; Braunschweig, Björn (Journal of Physical Chemistry B, 2014)
Mixtures of extgreekb-lactoglobulin (BLG) and sodium dodecyl sulfate (SDS) were studied at pH 3.8 and 6.7 under equilibrium conditions. At these pH conditions, BLG carries either a positive or a negative net charge, respectively, which enables tunable electrostatic interactions between anionic SDS surfactants and BLG proteins. For pH 3.8, vibrational sum-frequency generation (SFG) and ellipsometry indicate strong BLG–SDS complex formation at air–water interfaces that is caused by attractive electrostatic interactions. The latter complexes are already formed in the bulk solution which was confirmed by a thermodynamic study of BLG–SDS mixtures using isothermal titration calorimetry (ITC). For acidic conditions we determine from our ITC data an exothermal binding enthalpy of -40 kJ mol–1. Increasing SDS/BLG molar ratios above 10 leads to a surface excess of SDS and thus to a charge reversal from a positive net charge with BLG as the dominating surface adsorbed species to a negatively charged layer with SDS as the dominating surface species. The latter is evidenced by a pronounced minimum in SFG intensities that is also accompanied by a phase change of O–H stretching bands due to a reorientation of H2O within the local electric field. This phase change which occurs at SDS/BLG molar ratio between 1 and 10 causes a polarity change in SFG intensities from BLG aromatic C–H stretching vibrations. Conclusions from SFG spectra are corroborated by ellipsometry which shows a dramatic increase in layer thicknesses at molar ratios where a charge reversal occurs. The formation of interfacial multilayers comprising SDS-BLG complexes is, thus, caused by cancellation of electrostatic interactions which leads to agglomeration at the interface. In contrast to pH 3.8, behavior of BLG–SDS mixtures at pH 6.7 is different due to repulsive electrostatic interactions between SDS and BLG which lead to a significantly reduced binding enthalpy of -17 kJ mol–1. Finally, it has to be mentioned that SFG spectra show a coexistence of BLG and SDS molecules at the interface for BLG–SDS molar ratios > 2.
EAM Import::2019-03-12
Keywords: surface; tension; intermolecular; interaction; air; water; interface

Mobbing in Academia - Kamali, Mehdi; Hosseinpour, Saman; Swann, Jennifer; Sareh, Hossein Pooya; Mahmoudi, Morteza (A Brief Guide to Academic Bullying, 2021)

Mobility-Classified Mass Spectrometry Reveals a Complete Picture of the Electrospray Outcome - Lübbert, Christian; Peukert, Wolfgang (Journal of Physical Chemistry A, 2020)
Electrospray ionization mass spectrometry supported by mobility classification (ESI-DMA-MS) is a strong technique for a comprehensive analysis of organic and inorganic clusters and small nanoparticles. In-depth understanding and optimization of the electrospray process are key for unlocking new fields of application and for extension of the accessible range of data. We show that the combination of mobility-classified mass spectrometry (DMA-MS) with an electrospray operated in a well-defined cone-jet mode is capable of providing a full picture of the outcome of the electrospray process including the evaporation residues of the parent droplets. Based on ESI-DMA-MS measurements of lysozyme, we find that clusters up to almost 1 MDa (around 60 lysozyme molecules per cluster) formed as evaporation residues of the parent droplets can be detected. The escape probability of lysozyme molecules from the parent droplets is polarity-dependent. A quantitative analysis of clusters is possible at analyte concentrations where the likeliness of finding more than a single molecule in the generated droplet is low. At higher concentrations, one can, however, quantify the analyte concentration from the detected size of the droplet evaporation residues. The approach is widely applicable for organic and inorganic nanostructures. The results allow clear statements on the conditions under which mixtures of larger molecules, clusters, and nanoparticles are accessible to quantitative analysis by mass spectrometry.
CRIS-Team Scopus Importer:2020-11-06

Model for structure formation in nanosuspension droplet superheated steam drying - Bück, Andreas (Drying Technology, 2024)
In this work, a mathematical model for particle and structure formation from drying single nanosuspension droplets in superheated steam is presented. The influence of process and material conditions on structure formation (“locking”), especially shell properties is systematically investigated by computation. It is shown that with increasing superheating, larger and more porous particles result. Formed crusts decrease in thickness but are significantly denser than the overall particle. Differences in expected particle properties compared to conventional hot air drying are evaluated, indicating the existence of an “inversion temperature”. Effects of further heat and mass transfer processes (thermal radiation, nanoparticle aggregation, nanoparticle polydispersity, and anisotropy) on structure formation are qualitatively discussed.
CRIS-Team Scopus Importer:2024-10-18
Keywords: Droplet; drying; nanofluid; superheated vapor; suspension

Modeling adhesion forces between deformable bodies by FEM and Hamaker summation. - Peukert, Wolfgang; Zhou, Hongben (Langmuir, 2008)
A new numerical approach is presented for predicting adhesion forces of particles at flat and rough surfaces. The new hybrid method uses the finite element method (FEM) for the determination of elastic and plastic particle deformation combined with numerical Hamaker summation. In the numerical approach, the influence of the plastic deformation can be fully included. We show how the adhesion force depends on the contact geometry and the material properties. For easy comparison with other models, the force-displacement behavior of the systems is presented. The numerical approach is supported by atomic force microscopy (AFM) measurements. The experimentally observed adhesion force hysteresis is described very well by the new approach. Although calculations in this article are focused on spherical particles, our approach can be extended to particles of arbitrary shapes.
Keywords: finite; element; method; simulation; prediction; adhesion; deformation

Modeling, analysis and optimization of particle growth, nucleation and ripening by the way of nonlinear hyperbolic integro-partial differential equations - Gröschel, Michael; Peukert, Wolfgang; Leugering, Günter (Trends in PDE Constrained Optimization, 2014)
We consider the processes of particle nucleation, growth, precipitation and ripening via modeling by nonlinear 1-D hyperbolic partial integro differential equations. The goal of this contribution is to provide a concise predictive forward modeling of the processes including appropriate goal functions and to establish a mathematical theory for the open-loop optimization in this context. Beyond deriving optimality conditions in the synthesis process, we present the application of a fully implicit method for Ostwald ripening of ZnO quantum dots which preserves its numeric stability even with respect to the inherent high sensitivities and wide disparity of scales. FIMOR represents an appropriate method that can be integrated to subordinate optimization studies which enables its future application in the context of continuous particle syntheses and microreaction technology (MRT
Keywords: Numerical simulation; Nonlinear integro-partial differential equation; Ostwald ripening; Optimization; Particle synthesis; Particle growth

Modeling and Simulation of Process Technology for Nanoparticulate Drug Formulations-A Particle Technology Perspective. - Uhlemann, Jens; Diedam, Holger; Hoheisel, Werner; Schikarski, Tobias; Peukert, Wolfgang (Pharmaceutics, 2020)
Crystalline organic nanoparticles and their amorphous equivalents (ONP) have the potential to become a next-generation formulation technology for dissolution-rate limited biopharmaceutical classification system (BCS) class IIa molecules if the following requisites are met: (i) a quantitative understanding of the bioavailability enhancement benefit versus established formulation technologies and a reliable track record of successful case studies are available; (ii) efficient experimentation workflows with a minimum amount of active ingredient and a high degree of digitalization via, e.g., automation and computer-based experimentation planning are implemented; (iii) the scalability of the nanoparticle-based oral delivery formulation technology from the lab to manufacturing is ensured. Modeling and simulation approaches informed by the pharmaceutical material science paradigm can help to meet these requisites, especially if the entire value chain from formulation to oral delivery is covered. Any comprehensive digitalization of drug formulation requires combining pharmaceutical materials science with the adequate formulation and process technologies on the one hand and quantitative pharmacokinetics and drug administration dynamics in the human body on the other hand. Models for the technical realization of the drug production and the distribution of the pharmaceutical compound in the human body are coupled via the central objective, namely bioavailability. The underlying challenges can only be addressed by hierarchical approaches for property and process design. The tools for multiscale modeling of the here-considered particle processes (e.g., by coupled computational fluid dynamics, population balance models, Noyes-Whitney dissolution kinetics) and physiologically based absorption modeling are available. Significant advances are being made in enhancing the bioavailability of hydrophobic compounds by applying innovative solutions. As examples, the predictive modeling of anti-solvent precipitation is presented, and options for the model development of comminution processes are discussed.
Keywords: comminution; modeling and simulation; nanocrystal; oral bioavailability; pharmaceutical material science; poorly soluble drug; precipitation; product design

Modeling of inter- and intra-particle coating uniformity in a Wurster fluidized bed by a coupled CFD-DEM-Monte Carlo approach - Jiang, Zhaochen; Rieck, Christian; Bück, Andreas; Tsotsas, Evangelos (Chemical Engineering Science, 2020)
A coupled CFD-DEM and Monte Carlo approach was developed to investigate coating properties in a Wurster fluidized bed by considering gas flow, particle motion, droplet deposition, and the drying and solidifying of droplets on particle surfaces. Based on the spherical centroidal Voronoi tessellation (CVT), the Monte Carlo approach can model the deposition and splashing of spray droplets on the surface of individual particles. The capillary force induced by liquid bridges between particles was accounted in the DEM to investigate its influence on the coating and agglomeration behavior. The new model can provide information about the cycle time distribution, residence time distribution, coating coverage, uniformity of porosity (influenced by splashing) and layer thickness distributions on each individual particle (intra-particle) and in the particle population (inter-particle). The simulation results are compared with experimental data on residence time and intra-particle layer thickness distributions. Good agreement is observed between the simulation and the measurements.
CRIS-Team Scopus Importer:2019-10-29
Keywords: CFD-DEM; Coating; Monte Carlo; Surface coverage; Wurster fluidized bed

Modeling of Particle Behavior in a Wurster Fluidized Bed: Coupling CFD-DEM with Monte Carlo - Jiang, Z.; Rieck, C.; Bück, Andreas; Tsotsas, E. (IDS'2018: 21ST INTERNATIONAL DRYING SYMPOSIUM, 2018)
CFD-DEM approach is applied to investigate circulation motion of particles in a mono-disperse system under both dry and wetting conditions. Good agreement between simulation results and measurement data is observed, in terms of cycle time and residence time in dry condition. The deposition of droplets on the particle surface is modeled by a Monte Carlo approach. The influence of cohesion forces on the macroscopic particle circulation is discussed. In addition, information about coating coverage, the layer thickness and particle size distribution can be predicted by this integrating approac
CRIS-Team WoS Importer:2019-08-16
Keywords: CFD-DEM; Wurster coater; Monte Carlo; cohesion force; residence time; RESIDENCE TIME

Modelling and Efficiency Enhancement of Tablet Coating in a Rotary Drum - Bück, Andreas; Singh, Abhinandan Kumar; Palis, Stefan (Lecture Notes in Electrical Engineering, 2025)
The paper focuses on optimizing coating efficiency in pharmaceutical tablet production. Coating tablets with active pharmaceutical ingredients (APIs) is crucial for controlling release rates. The process involves spraying a liquid onto a mixed tablet bed, where it forms a solid coating through evaporation. Homogeneity in coating thickness is vital for consistent API release. The study proposes a Monte-Carlo model for a rotary drum spray coater. Experimental validation shows good agreement between simulated and observed coating thickness distributions. Based on the proposed model different real-time optimization algorithms are explored to improve coating efficiency. Results highlight the importance of optimizing coating parameters for efficient and uniform tablet production, crucial for pharmaceutical quality control and cost-effectiveness.
CRIS-Team Scopus Importer:2025-05-09
Keywords: coating efficiency; Monte-Carlo simulation; real-time optimization; pharmaceutical tablet production; Tablet coating

Modelling and simulation of water profiles in a partially filled horizontal drum at low airflow rate - Rezendes Tada, Erika Fernanda; Bück, Andreas; Casciatori, F. P.; Thoméo, João Cláudio (23rd International Congress of Chemical and Process Engineering (CHISA 2018) and 21st Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction (PRES 2018), 2018)
Keywords: Solid State Fermentation; Cellulases; Aspergillus Niger

Modelling of grinding in an air classifier mill based on a fundamental material function - Peukert, Wolfgang; Vogel, Lutz (KONA Powder and Particle Journal, 2003)
An approach to quantifying the impact grinding per formance of dif ferent materials is presented. Based on a dimensional analysis and on fracture mechanical considerations, two material parameters, f Mat.and W m,min, are derived theoretically. fMat . characterises the resistance of particulate material  against  fracture  during  impact  comminution.  Wm,min gives  the  mass-specif ic  energy  which  aparticle can absorb without fracture. Using this approach, various materials over a wide size range, e.g.  dif ferent  polymers,  crystalline  substances,  glass  and  limestone,  can  be characterised  quantitatively.  The  derived  material  parameters  are  applied  to  the  systematic  modelling  of  grinding  in impact mills. A population balance model is presented and the results of the simulation for an air classifier mill are shown. The developed model permits a clear separation of the inf luence of material properties, mill-specif ic features and operating conditions, thus enabling a deeper understanding of the impact grinding process
UnivIS-Import:2015-03-09:Pub.2004.tech.ITC.mechve.modell
Keywords: grinding; comminution; milling

Modelling the superposition of grinding and agglomeration in stirred ball mills by population balance models - Peukert, Wolfgang; Stenger, Frank; Sommer, Marc; Wagner, N; Diemer, R (Proceedings PARTEC 2004, 2004)
UnivIS-Import:2015-04-16:Pub.2004.tech.ITC.mechve.modell_5

Modelling the two-dimensional growth and oriented attachment of goethite nanorods synthesized via oxidation of aqueous ferrous hydroxide slurries - Güldenpfennig, Andreas; Distaso, Monica; Klupp Taylor, Robin; Peukert, Wolfgang (Chemical Engineering Journal, 2018)
Keywords: Anisotropic growth; Goethite; 2D model; 3-Phase reaction; Oriented attachment; Reaction rate

Modelling titania formation at typical industrial process conditions: Effect of surface shielding and surface energy on relevant growth mechanisms - Artelt, Christian; Schmid, Hans-Joachim; Peukert, Wolfgang (Chemical Engineering Science, 2006)
This work investigates the effects of reduced accessible surface area of aggregate particles and of surface energy on relevant particle formation and growth mechanisms during titania formation from the vapour phase at industrial process conditions. Growth due to surface reaction and due to condensation is related to the fraction of the surface area that is exposed to the collision with single molecules. Surface shielding is found to hamper surface reaction and condensation once fractal aggregates start to form. It leads to significantly retarded precursor consumption and produces aggregate particles, which consist of more, but smaller primary particles. Surface energy data are varied within a range as proposed by available literature data. Moderate and high surface energy values result in a thermodynamic barrier to the formation of new particles and are shown to reduce the formation of seed particles by several orders of magnitude. This leads to the formation of aggregate particles which consist of a rather small number of primary particles and mainly grow by surface reaction. The primary contribution of condensation to growth of individual primary particles is shown to be very little. However, condensation should not be neglected as it has a strong impact on particle formation rates and hence on product characteristics such as the number of primary particles and primary particle siz
Keywords: Surface energy; Surface shielding; Nanoparticles; Population balance; Titania; Condensation; Aerosol process simulations

Model Reduction, Structure-property Relations and Optimization Techniques for the Production of Nanoscale Particles - Gröschel, Michael; Leugering, Günter; Peukert, Wolfgang (International Series of Numerical Mathematics, 2011)
The production of nanoscaled particulate products with exactly pre-defined characteristics is of enormous economic relevance. Although there are different particle formation routes they may all be described by one class of equations. Therefore, simulating such processes comprises the solution of nonlinear, hyperbolic integro-partial differential equations. In our project we aim to study this class of equations in order to develop efficient tools for the identification of optimal process conditions to achieve desired product properties. This objective is approached by a joint effort of the mathematics and the engineering faculty. Two model-processes are chosen for this study, namely a precipitation process and an innovative aerosol process allowing for a precise control of residence time and temperature. Since the overall problem is far too complex to be solved directly a hierarchical sequence of simplified problems has been derived which are solved consecutively. In particular, the simulation results are finally subject to comparison with experiments.
Keywords: Population balance equations; optimal control; model reduction; parameter identification

Molecular dynamics simulations of the contact between two NaCl nanocrystals - Peukert, Wolfgang; Götzinger, Martin; Miesbauer, Oliver (Nanotechnology, 2003)
The contact between two NaCl nano-crystals consisting of 6000–15 000 atoms was studied using molecular dynamics computer simulations. After placing two NaCl cuboids at varying distances, the adhesion forces and the resulting strains were measured. We observed jump to contact and found there is an upper limit of distance. Similarly, NaCl hemispheres possessing radii equal to 2.13, 3.26 and 4.15 nm were placed at varying distances from a NaCl cuboid. The relations between distance and force were determined. In the case of an indentation, the relations were described by power functions and compared with the widely used Hertzian theory. We were able to show that the exponent of the power function rises with increasing radius of the hemisphere. It apparently converges to a value of 1.5, which is in agreement with the Hertzian theory. It thus seems justified to assume that the studied system can be adequately described with continuum mechanics down to sizes of 5 nm. But for smaller systems continuum mechanics appears not to be adequate.
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.molecu
Keywords: nano; crystal; dynamic; simulation

Molecular-Induced Chirality Transfer to Plasmonic Lattice Modes - Görlitzer, Eric; Zapata-Herrera, Mario; Ponomareva, Ekaterina; Feller, Déborah; Garcia-Etxarri, Aitzol; Karg, Matthias; Aizpurua, Javier; Vogel, Nicolas (ACS Photonics, 2023)
Molecular chirality plays fundamental roles in biology. The chiral response of a molecule occurs at a specific spectral position, determined by its molecular structure. This fingerprint can be transferred to other spectral regions via the interaction with localized surface plasmon resonances of gold nanoparticles. Here, we demonstrate that molecular chirality transfer occurs also for plasmonic lattice modes, providing a very effective and tunable means to control chirality. We use colloidal self-assembly to fabricate non-close packed, periodic arrays of achiral gold nanoparticles, which are embedded in a polymer film containing chiral molecules. In the presence of the chiral molecules, the surface lattice resonances (SLRs) become optically active, i.e., showing handedness-dependent excitation. Numerical simulations with varying lattice parameters show circular dichroism peaks shifting along with the spectral positions of the lattice modes, corroborating the chirality transfer to these collective modes. A semi-analytical model based on the coupling of single-molecular and plasmonic resonances rationalizes this chirality transfer. © 2023 The Authors. Published by American Chemical Societ
Keywords: chirality transfer; nanoparticles; chirality; nanophotonics; surface lattice resonances

Molecular Mie model for second harmonic generation and sum frequency generation - Wunderlich, Sarina; Schürer, Benedikt; Sauerbeck, Christian; Peukert, Wolfgang; Peschel, Ulf (Physical Review B, 2011)
A theoretical model to simulate second harmonic and sum frequency generation from stratified spherical particles of arbitrary material is presented and compared with the widely used Rayleigh-Gans-Debye approximation and to experimental results from polystyrene particles with adsorbed malachite green molecules. In this model, the nonlinear polarization is caused by individual dipoles placed in the vicinity of the sphere and is simulated on a molecular basis. This offers greater flexibility to model more sophisticated systems.

Molecular order of mixed self-assembled monolayers studied by surface vibrational spectroscopy - Rumpel, Armin; Novak, Michael; Braunschweig, Björn; Halik, Marcus; Peukert, Wolfgang (Materials Engineering and Sciences Division - Core Programming Topic at the 2011 AIChE Annual Meeting, 2011)

Molecular structure of octadecylphosphonic acids during their self-assembly on α-Al2O3(0001) - Meltzer, Christian; Yu, Hui; Peukert, Wolfgang; Braunschweig, Björn (Physical Chemistry Chemical Physics, 2018)

Monitoring of Flow-Induced Aggregation and Conformational Change of Monoclonal Antibodies - Wolfrum, Sonja; Weichsel, Ulrike; Siedler, Michael; Weber, Carsten; Peukert, Wolfgang (Chemie Ingenieur Technik, 2017)
Keywords: Mechanical stress; Protein aggregation; Extrinsic fluorescent dyes; In situ methods; Fluorescence spectroscopy

Monitoring structure formation changes of amphiphilic polyesters in different. solvents by hyper-rayleigh scattering (HRS) - Schneider, Lars; Voronov, Andriy; Kohut, Ananiy; Peukert, Wolfgang (2007 AIChE Annual Meeting, 2007)

Monte Carlo modeling of binder-Less spray agglomeration in fluidized beds - Rieck, Christian; Schmidt, Martin; Bück, Andreas; Tsotsas, Evangelos (Aiche Journal, 2018)
Fluidized bed spray agglomeration is used in the industry to increase the particle size and to improve several properties, for example, bulk density, flowability, and dissolution behavior of particulate products. Usually, a binder liquid is sprayed on a particle bed. If amorphous materials are used, spraying of pure water may cause agglomeration due to glass transition at wet spots on the particle surface. As no process models covering binder‐less spray agglomeration currently exist, a model based on a Monte Carlo method is presented. In this method, the process is described by events and processes on the single particle scale. Additionally, agglomeration experiments in a lab‐scale fluidized bed using three different maltodextrins are presented. For each experiment, a simulation was performed. The simulation results are compared with the obtained experimental dat
Keywords: maltodextrin; spray fluidized bed; agglomeration; glass transition

Monte Carlo modeling of spray agglomeration in a cylindrical fluidized bed: From batch-wise to continuous processes - Du, J.; Strenzke, G.; Bück, Andreas; Tsotsas, E. (Powder Technology, 2022)
Monte Carlo method is a stochastic approach that can simulate different micro-mechanisms occurring in spray fluidized bed (SFB) agglomeration. As no model covered the simulation of continuous SFB agglomeration process existing before, an event-driven constant volume Monte Carlo model is proposed. By adding particle feed and discharge events that take place periodically, the Monte Carlo model is extended to simulate continuous SFB agglomeration process. In these events, new particles are fed, and individuals are randomly selected and removed according to the feed rate and the change in bed mass. The experimental results show that the decrease of feed rate or bed mass increases the particle size. The comparison of experimental and simulation results shows that the continuous Monte Carlo model can predict the evolution of the particle size distribution with collision frequency prefactor 0.05 and breakage probability 0.17%. The development of bed mass in experiments can be reproduced in the simulations. (c) 2021 Elsevier B.V. All rights reserved.
CRIS-Team WoS Importer:2021-11-26

Monte Carlo simulation of aggregate morphology for simultaneous coagulation and sintering - Peukert, Wolfgang; Schmid, Hans-Joachim; Tejwani, Saurabh; Artelt, Christian (Journal of Nanoparticle Research, 2004)
A model for simulation of the three-dimensional morphology of nano-structured aggregates formed by concurrent coagulation and sintering is presented. Diffusion controlled cluster-cluster aggregation is assumed to be the prevailing coagulation mechanism which is implemented using a Monte-Carlo algorithm. Sintering is modeled as a successive overlapping of spherical primary particles, which are allowed to grow as to preserve overall mass. Simulations are characterized by individual ratios τ of characteristic collision to fusion time. A number of resulting aggregate-structures is displayed and reveals structure formation by coagulation and sintering for different values of τ. These aggregates are described qualitatively and quantitatively by their mass fractal dimension Df and radius of gyration. The fractal dimension increases from 1.86 for pure aggregation to ≈ 2.75 for equal characteristic time scales. As sintering turns out to be more and more relevant, increasingly compact aggregates start to form and the radius of gyration decreases significantly. The simulation results clearly reveal a strong dependence of the fractal dimension on the kinetics of the concurrent coagulation and sintering processes. Considering appropriate values of D f in aerosol process simulations may therefore be important in many cases. © 2005 Springer.
UnivIS-Import:2015-03-09:Pub.2004.tech.ITC.mechve.montec
Keywords: Aerosol process simulation; Aggregate structure formation; Coagulation and sintering; Fractal dimension; Radius of gyration

Morphological descriptors of agglomerates produced in continuously operated spray fluidized beds - Strenzke, G.; Janocha, M.; Bück, Andreas; Tsotsas, E. (Powder Technology, 2022)
This work presents the results of a systematic investigation of structural and morphological descriptors of agglomerates produced in continuously operated fluidized bed spray agglomeration. Experiments with glass beads as primary particles and a water-based HPMC mixture as top sprayed binder solution were carried out within a cylindrical fluidized bed of pilot plant scale. Characterization of all agglomerates was performed by X-ray micro-computed tomography. Investigated descriptors include number of primary particles, radius of gyration, coordination number and angle distribution as well as porosity and fractal properties. Utilizing these descriptors, a comparison regarding morphology of agglomerates produced in batch and continuous operation under similar process conditions and process times is drawn.
CRIS-Team Scopus Importer:2022-01-21
Keywords: Fluidized bed; Internal structure; Morphological descriptors; Spray agglomeration; X-ray computed tomography

Morphological impact of zinc oxide layers on the device performance in thin-film transistors - Faber, Hendrik; Klaumünzer, Martin; Voigt, Michael; Galli, Diana; Vieweg, Benito; Peukert, Wolfgang; Spiecker, Erdmann; Halik, Marcus (Nanoscale, 2011)
Zinc oxide thin-films are prepared either by spin coating of an ethanolic dispersion of nanoparticles (NP, diameter 5 nm) or by spray pyrolysis of a zinc acetate dihydrate precursor. High-resolution electron microscopy studies reveal a monolayer of particles for the low temperature spin coating approach and larger crystalline domains of more than 30 nm for the spray pyrolysis technique. Thin-film transistor devices (TFTs) based on spray pyrolysis films exhibit higher electron mobilities of up to 24 cm² V−1 s−1 compared to 0.6 cm² V−1 s−1 for NP based TFTs. These observations were dedicated to a reduced number of grain boundaries within the transistor channel.

Morphology-Graded Silicon Nanowire Arrays via Chemical Etching: Engineering Optical Properties at the Nanoscale and Macroscale - Wendisch, Fedja J.; Abazari, Mehri; Mahdavi, Hossein; Rey, Marcel; Vogel, Nicolas; Musso, Maurizio; Diwald, Oliver; Bourret, Gilles R. (ACS Applied Materials and Interfaces, 2020)
We report on a quick, simple, and cost-effective solution-phase approach to prepare centimeter-sized morphology-graded vertically aligned Si nanowire arrays. Gradients in the nanowire diameter and shape are encoded through the macroscale substrate via a "dip-etching" approach, where the substrate is removed from a KOH etching solution at a constant rate, while morphological control at the nanowire level is achieved via sequential metal-assisted chemical etching and KOH etching steps. This combined approach provides control over light absorption and reflection within the nanowire arrays at both the macroscale and nanoscale, as shown by UV-vis spectroscopy and numerical three-dimensional finite-difference time-domain simulations. Macroscale morphology gradients yield arrays with gradually changing optical properties. Nanoscale morphology control is demonstrated by synthesizing arrays of bisegmented nanowires, where the nanowires are composed of two distinct segments with independently controlled lengths and diameters. Such nanowires are important to tailor light-matter interactions in functional devices, especially by maximizing light absorption at specific wavelengths and locations within the nanowires.
CRIS-Team Scopus Importer:2020-03-20
Keywords: colloidal lithography; graded substrate; KOH etching; metal-assisted chemical etching; Si nanowire arrays; structural colors

Multiband Hypersound Filtering in Two-Dimensional Colloidal Crystals: Adhesion, Resonances, and Periodicity - Graczykowski, Bartlomiej; Vogel, Nicolas; Bley, Karina; Butt, Hans Jürgen; Fytas, George (Nano Letters, 2020)
The hypersonic phonon propagation in large-area two-dimensional colloidal crystals is probed by spontaneous micro Brillouin light scattering. The dispersion relation of thermally populated Lamb waves reveals multiband filtering due to three distinct types of acoustic band gaps. We find Bragg gaps accompanied by two types of hybridization gaps in both sub- and superwavelength regimes resulting from contact-based resonances and nanoparticle eigenmodes, respectively. The operating GHz frequencies can be tuned by particle size and depend on the adhesion at the contact interfaces. The experimental dispersion relations are well represented by a finite element method model enabling identification of observed modes. The presented approach also allows for contactless study of the contact stiffness of submicrometer particles, which reveals size effect deviating from macroscopic predictions.
CRIS-Team Scopus Importer:2020-03-10
Keywords: acoustic band gap; Brillouin light scattering; Colloidal crystals; GHz signal filtering; Lamb waves; phononics

Multi-component and multi-phase population balance model: The case of Georgeite formation as methanol catalyst precursor phase - Hartig, Martin Andreas Johannes; Jacobsen, Nikolas; Peukert, Wolfgang (Chemical Engineering Science, 2014)
A novel generally applicable multi-component and multi-phase population balance model is presented. The model classifies precipitation and crystallization systems into the number of components (i.e. building units of solid) and number of solid phases. The model includes reaction equilibria of metal ions in aqueous media, activity modeling, mixing, particle formation kinetics, population and mole balances. The new model is applied to the initial stages of copper catalyst precursor formation. The population balance model is simplified to a single-solid phase and multi-component precipitation. Simulations for several solid phases were performed at various experimental conditions. We show that the formation of the carbonate rich Georgeite phase is favored. The simulation results are verified by the measured global parameters pH and solid weight. Mixing plays a minor role in comparison to the variation of the reactant concentration. The timescale of precipitation including mixing, nucleation and crystal growth ranges from microseconds up to 1 s depending on the extent of secondary nucleation.
Keywords: multi-component; catalysis; solid; phase; mixing; aqeous; georgeite

Multidimensional Analysis of Nanoparticles with Highly Disperse Properties Using Multiwavelength Analytical Ultracentrifugation - Walter, Johannes; Löhr, Konrad; Karabudak, Engin; Reis, Wieland; Mikhael, Jules; Peukert, Wolfgang; Wohlleben, Wendel; Coelfen, Helmut (ACS nano, 2014)
The worldwide trend in nanoparticle technology toward increasing complexity must be directly linked to more advanced characterization methods of size, shape and related properties, applicable to many different particle systems in science and technology. Available techniques for nanoparticle characterization are predominantly focused on size characterization. However, simultaneous size and shape characterization is still an unresolved major challenge. We demonstrate that analytical ultracentrifugation with a multiwavelength detector is a powerful technique to address multidimensional nanoparticle analysis. Using a high performance optical setup and data acquisition software, information on size, shape anisotropy and optical properties were accessible in one single experiment with unmatched accuracy and resolution. A dynamic rotor speed gradient allowed us to investigate broad distributions on a short time scale and differentiate between gold nanorod species including the precise evaluation of aggregate formation. We report how to distinguish between different species of single-wall carbon nanotubes in just one experiment using the wavelength-dependent sedimentation coefficient distribution without the necessity of time-consuming purification methods. Furthermore, CdTe nanoparticles of different size and optical properties were investigated in a single experiment providing important information on structure-property relations. Thus, multidimensional information on size, density, shape and optical properties of nanoparticulate systems becomes accessible by means of analytical ultracentrifugation equipped with multiwavelength detectio
Keywords: nanoparticle; characterization; analytical; ultracetrifugation; CdTe; multidimensional

Multidimensional characterization of noble metal alloy nanoparticles by multiwavelength analytical ultracentrifugation - Cardenas Lopez, Paola Ivonne; Uttinger, Maximilian; Traore, Nabi; Khan, Hamzah; Drobek, Dominik; Apeleo Zubiri, Benjamin; Spiecker, Erdmann; Pflug, Lukas; Peukert, Wolfgang; Walter, Johannes (Nanoscale, 2022)
In this study, we introduce a method for the simultaneous retrieval of two-dimensional size-composition distributions of noble metal Ag-Au alloy nanoparticles utilizing an analytical ultracentrifuge equipped with a multiwavelength extinction detector (MWL-AUC). MWL-AUC is used to measure coupled optical and sedimentation properties of the particles. The optical response of the nanoparticles is calculated using Mie's theory, where the particles' complex refractive index is corrected due to the effect of reduced mean free path of electrons. Using a combined analysis of the hydrodynamic and spectral data captured by MWL-AUC, the size and composition of the alloy particles is retrieved. Our method is validated through the analysis of synthetic data and by the very good agreement between experimental scanning transmission electron microscopy and our AUC data. The presented comprehensive characterization approach contributes to improved synthesis, scale-up and production of particulate systems as it provides a simple, fast and direct method to determine noble metal alloy nanoparticle size and composition distributions simultaneously.
CRIS-Team WoS Importer:2022-09-09

Multidimensional Fractionation of Particles - Frank, Uwe; Dienstbier, Jana; Tischer, Florentin; Wawra, Simon; Gromotka, Lukas; Walter, Johannes; Liers-Bergmann, Frauke; Peukert, Wolfgang (Separations, 2023)
The increasing complexity in particle science and technology requires the ability to deal with multidimensional property distributions. We present the theoretical background for multidimensional fractionations by transferring the concepts known from one dimensional to higher dimensional separations. Particles in fluids are separated by acting forces or velocities, which are commonly induces by external fields, e.g., gravitational, centrifugal or electro-magnetic fields. In addition, short-range force fields induced by particle interactions can be employed for fractionation. In this special case, nanoparticle chromatography is a recent example. The framework for handling and characterizing multidimensional separation processes acting on multidimensional particle size distributions is presented. Illustrative examples for technical realizations are given for shape-selective separation in a hydrocyclone and for density-selective separation in a disc separator.
Keywords: multidimensional separation; two-dimensional property distribution; size; shape; composition

Multidimensional Nanoparticle Characterization by Means of Analytical Ultracentrifugation and Multiwavelength Detection - Peukert, Wolfgang; Nacken, Thomas; Walter, Johannes; Thajudeen, Thaseem; Segets, Doris; Sherwood, Peter; Stafford, Walter (Chemie Ingenieur Technik, 2016)
Keywords: Nanoparticle; centrifugation

Multidimensional Particle Size Distributions and Their Application to Nonspherical Particle Systems in Two Dimensions - Frank, Uwe; Wawra, Simon; Pflug, Lukas; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2019)
Particle science and technology evolve toward ever increasing complexity with respect to the multidimensional particle properties of size, shape, surface, internal structure, and composition. In this study, the theoretical background is elaborated for multidimensional particle size distributions (PSDs) by transferring the concepts known from 1D size distributions to anisotropic particles comprising at least two different length dimensions, e.g., nanorods and platelets. After introducing 2D PSDs, the calculation of differently weighted probability density functions including their interconversion is presented. This is necessary in order to compare data resulting from different measurement techniques which probe different physical properties and thus provide differently weighted PSDs. In addition, it is shown how 1D distributions with reduced content of information can be deduced from 2D PSDs. As a proof-of-concept and for illustration purposes, this approach is applied to a 2D Gaussian size distribution. Furthermore, a generalized scheme is suggested which outlines the conversion of number, surface, and volume weighted densities within the 2D space. The application of these methods to the more general n-dimensional case is straightforward.
CRIS-Team Scopus Importer:2019-06-04
Keywords: 2D distributions; multidimensional characterization; particle size distributions; particle technology

Multifunctional, Hybrid Materials Design via Spray-Drying: Much more than Just Drying - Wintzheimer, Susanne; Luthardt, Leoni; Cao, Kiet Le Anh; Imaz, Inhar; Maspoch, Daniel; Ogi, Takashi; Bück, Andreas; Debecker, Damien P.; Faustini, Marco; Mandel, Karl (Advanced Materials, 2023)
Spray-drying is a popular and well-known “drying tool” for engineers. This perspective highlights that, beyond this application, spray-drying is a very interesting and powerful tool for materials chemists to enable the design of multifunctional and hybrid materials. Upon spray-drying, the confined space of a liquid droplet is narrowed down, and its ingredients are forced together upon “falling dry.” As detailed in this article, this enables the following material formation strategies either individually or even in combination: nanoparticles and/or molecules can be assembled; precipitation reactions as well as chemical syntheses can be performed; and templated materials can be designed. Beyond this, fragile moieties can be processed, or “precursor materials” be prepared. Post-treatment of spray-dried objects eventually enables the next level in the design of complex materials. Using spray-drying to design (particulate) materials comes with many advantages—but also with many challenges—all of which are outlined here. It is believed that multifunctional, hybrid materials, made via spray-drying, enable very unique property combinations that are particularly highly promising in myriad applications—of which catalysis, diagnostics, purification, storage, and information are highlighte
Keywords: structure formation; spray-drying; nanoparticle assembly; hybrid materials; supraparticles; chemistry in a droplet; functional materials

Multifunctional performance of core–shell rGO@Fe3O4 on the mechanical, electrical/thermal, EMI, and microstructure properties of cement-based composites - Imanian Ghazanlou, Siamak; Imanian Ghazanlou, Siavash; Imanian Ghazanlou, Sroush; Karimi, Hamid; Azimi, Neda; Hosseinpour, Saman (Construction and Building Materials, 2023)
This research study focuses on the development of a multifunctional cement nanocomposite using reduced graphene oxide (rGO) nanosheets. To address the challenges of rGO dispersion, a core–shell structure of rGO@Fe3O4 (rGO@F) was investigated in cement paste. The rGO@F nanohybrid was thoroughly characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The main objectives of this study were to improve the mechanical properties, electrical conductivity, thermal conductivity, and chemical properties of the cement composite through the incorporation of rGO@F. The performance of the cement paste containing rGO0.1@Fe3O4 (0.1 wt% rGO and 1 wt% Fe3O4) was evaluated, and it was found that its toughness and compressive strength were significantly enhanced compared to the reference sample. Furthermore, the addition of rGO@F led to a remarkable increase in the electrical and thermal conductivity of the modified cement composite, attributed to the formation of conductive pathways facilitated by the rGO nanosheets. Comprehensive analyses including XRD, TGA, differential scanning calorimetry (DSC), thermally assisted microscopy (TAM), FTIR, and X-ray photoelectron spectroscopy (XPS) confirmed that the rGO@F nanohybrid had a significant impact on the chemical properties and hydration process of the hardened cement paste. SEM images revealed a more compact microstructure of the cement paste in the presence of rGO@F, demonstrating its role in crack inhibition. Additionally, an increase in the formation of improved hydration crystals such as tobermorite and jennite was observed. The core–shell structure of rGO@F exhibited exceptional electromagnetic wave absorption properties due to its layered configuration, effectively trapping the electromagnetic waves. Overall, this research study highlights the successful fabrication of a multifunctional cement nanocomposite through the incorporation of rGO@F. The findings demonstrate significant improvements in mechanical strength, electrical conductivity, thermal conductivity, chemical properties, crack inhibition, and electromagnetic wave absorption. This research contributes to the advancement of cement-based materials with enhanced performance and opens up avenues for various applications in fields such as construction, infrastructure, and telecommunications.
CRIS-Team Scopus Importer:2023-07-07
Keywords: Cement; EMI wave shielding; Fe; Mechanical properties; rGO

Multi-rate data fusion for state and parameter estimation in (Bio-)chemical process engineering - Dürr, Robert; Duvigneau, Stefanie; Seidel, Carsten; Kienle, Achim; Bück, Andreas (Processes, 2021)
For efficient operation, modern control approaches for biochemical process engineering require information on the states of the process such as temperature, humidity or chemical composi-tion. Those measurement are gathered from a set of sensors which differ with respect to sampling rates and measurement quality. Furthermore, for biochemical processes in particular, analysis of physical samples is necessary, e.g., to infer cellular composition resulting in delayed information. As an alternative for the use of this delayed measurement for control, so-called soft-sensor approaches can be used to fuse delayed multirate measurements with the help of a mathematical process model and provide information on the current state of the process. In this manuscript we present a complete methodology based on cascaded unscented Kalman filters for state estimation from delayed and multi-rate measurements. The approach is demonstrated for two examples, an exothermic chemical reactor and a recently developed model for biopolymer production. The results indicate that the the current state of the systems can be accurately reconstructed and therefore represent a promising tool for further application in advanced model-based control not only of the considered processes but also of related processes.
Created from Fastlane, Scopus look-up
Keywords: Bayesian estimation; Model identifi-cation; Multisensor data fusion; Unscented Kalman filtering

Multi-stage and multi-compartment model for dynamic simulation of horizontal fluidized bed granulator - Mielke, Lisa; Bück, Andreas; Tsotsas, Evangelos (Drying Technology, 2019)
This work presents a multi-chamber and multi-compartment model of a horizontal fluidized bed apparatus for layering granulation, coating, and drying. Each chamber is designed individually and process conditions, such as spray rate, particle feed or gas temperature, can be adjusted for each chamber separately. Particle growth is described by population balance modeling. The characteristics of the particle exchange rates between the individual process chambers are determined by separation functions to account for different weir configurations. Additionally a drying model is presented that takes initial droplet size and contact angle as well as partial wetting of the particle surface into account. Because of the great variety of parameters that influence this model, a parametric study is carried out to identify how construction or process parameters affect the product quality. The influence of different separation functions, thermal process conditions, and initial droplet properties on key product quality features such as particle size distribution, product moisture content, and degree of surface wetting are presented and discussed. The developed model can be used to describe product quality and particle transport in complex horizontal fluidized bed apparatuses.
CRIS-Team WoS Importer:2019-12-17

Multi-zone & multi-compartment model for dynamic simulation of horizontal fluidized bed granulator - Mielke, L.; Bück, Andreas; Tsotsas, E. (IDS'2018: 21ST INTERNATIONAL DRYING SYMPOSIUM, 2018)
Due to the ongoing development and implementation of process control and observation techniques in production processes of particulate products, the research on complexly designed process apparatuses has become of great interest. The work presented in this paper is focused on a model-based study on a multi-chamber horizontal fluidized bed apparatus for fluidized bed layering granulation. The model for the solid phase is extended by a new drying model. Because of the great variety of parameters that influence this complex system a preliminary model-based study on a simplified setup shall show which construction or process parameters influence the product qualit
CRIS-Team WoS Importer:2019-08-16
Keywords: fluidized bed granulation; population balance modeling; surface moisture content; drying; PARTICLE FORMULATION

Nanogap-controllable self-assembly of gold nanoparticles using nanotrench template - Sugano, Kouji; Hiraoka, Ryoji; Tsuchiya, Toshiyuki; Tabata, Osamu; Klaumünzer, Martin; Voigt, Michael; Peukert, Wolfgang (2011 16th International Solid-State Sensors, Actuators and Microsystems Conference, TRANSDUCERS'11, 2011)
This paper reports high-yield self-assembly process for gold nanoparticle with a diameter of 60 nm, which can precisely control an interparticle nanogap ranging from 0 to 60 nm, using a template-assisted self-assembly with a pair of circular nanotrenches. A center-to-center distance of nanotrenches was changed in order to control an interparticle nanopgap. We found that an assembly yield strongly depends on a particle-particle interaction and achieved nanogap-controlled particle arrangement with high yield by controlling the particle-particle interaction with an addition of an electrolyte. This technique would enable us to control plasmonic resonance property of a nanoparticles pair for many emerging applications. © 2011 IEE
Keywords: Nanoparticle; Nanogap; Self-Assembly; Plasmon

Nanogels with tailored hydrophobicity and their behavior at air/water interfaces - Cui, Ruiguang; Ickler, Maret; Menath, Johannes; Vogel, Nicolas; Klinger, Daniel (Soft Matter, 2025)
The interfacial behavior of micro-/nanogels is governed to a large extent by the hydrophobicity of their polymeric network. Prevailing studies to examine this influence mostly rely on external stimuli like temperature or pH to modulate the particle hydrophobicity. Here, a sudden transition between hydrophilic and hydrophobic state prevents systematic and gradual modulation of hydrophobicity. This limits detailed correlations between interfacial behavior and network hydrophobicity. To address this challenge, we introduce a nanogel platform that allows accurate tuning of hydrophobicity on a molecular level. For this, via post-functionalization of active ester- based particles, we prepare poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA) nanogels as a hydrophilic benchmark and introduce gradually varied amounts of hydrophobic propyl or dodecyl moieties to increase the nanogel hydrophobicity. We study the deformation and arrangement of these particles at an air/water interface and correlate the results with quantitative measures for nanogel hydrophobicity. We observe that increasing hydrophobicity of nanogels, either by increasing the hydrophobic moiety ratio or the alkyl chain length, leads to decreased particle deformability and aggregation of an interfacially-adsorbed monolayer. Contrary to what may be intuitively assumed, these changes are not gradual, but rather occur suddenly above a threshold in hydrophobicity. Our study further shows that the effect of hydrophobicity affects the nanogel properties differently in bulk and when adsorbed at liquid interfaces. Thus, this study establishes the transition of interfacial behavior between soft gel-like particles to a solid spherical morphology triggered by the increase in hydrophobicit
Keywords: Benchmarking; Chain length; Microgels; Monolayers; Nanoclay; Nanopores; Active esters; Air/Water Interfaces; External stimulus; Hydrophilic and hydrophobic; Interfacial behaviors; Molecular levels; Nanogels; Particle hydrophobicity; Polymeric networks; Postfunctionalization; Nanogels

Nanoimprint Lithography Facilitated Plasmonic-Photonic Coupling for Enhanced Photoconductivity and Photocatalysis - Gupta, Vaibhav; Sarkar, Swagato; Aftenieva, Olha; Tsuda, Takuya; Kumar, Labeesh; Schletz, Daniel; Schultz, Johannes; Kiriy, Anton; Fery, Andreas; Vogel, Nicolas; König, Tobias A.F. (Advanced Functional Materials, 2021)
Imprint lithography has emerged as a reliable, reproducible, and rapid method for patterning colloidal nanostructures. As a promising alternative to top-down lithographic approaches, the fabrication of nanodevices has thus become effective and straightforward. In this study, a fusion of interference lithography (IL) and nanosphere imprint lithography on various target substrates ranging from carbon film on transmission electron microscope grid to inorganic and dopable polymer semiconductor is reported. 1D plasmonic photonic crystals are printed with 75% yield on the centimeter scale using colloidal ink and an IL-produced polydimethylsiloxane stamp. Atomically smooth facet, single-crystalline, and monodisperse colloidal building blocks of gold (Au) nanoparticles are used to print 1D plasmonic grating on top of a titanium dioxide (TiO2) slab waveguide, producing waveguide-plasmon polariton modes with superior 10 nm spectral line-width. Plasmon-induced hot electrons are confirmed via two-terminal current measurements with increased photoresponsivity under guiding conditions. The fabricated hybrid structure with Au/TiO2 heterojunction enhances photocatalytic processes like degradation of methyl orange (MO) dye molecules using the generated hot electrons. This simple colloidal printing technique demonstrated on silicon, glass, Au film, and naphthalenediimide polymer thus marks an important milestone for large-scale implementation in optoelectronic devices.
CRIS-Team Scopus Importer:2021-07-09
Keywords: colloidal nanospheres; nanoimprint lithography; photocatalysis; plasmon-induced charge transfer; waveguide-plasmon polariton

Nanomilling in stirred media mills - Peukert, Wolfgang; Stenger, Frank; Mende, Stefan; Schwedes, Jörg (Chemical Engineering Science, 2005)
This paper investigates the production of stable nanoparticle suspensions. The experimental set-up allows the online measurement of the most important electrochemical properties and the particle size distribution of the product suspension as well as an adjustment of the pH-value for stabilization during the comminution process. Electrostatic stabilization is a strong tool to produce stable nanoparticle suspensions for sparingly soluble oxide components. In this contribution the influence of different operational parameters at stable suspensions properties on the grinding result in the nanometer size range is presented. In addition to alumina, the concept of electrostatic stabilization during wet grinding of nanoparticles is also applied to tin oxide. © 2005 Elsevier Ltd. All rights reserved.
Keywords: Comminution; Interface; Oxide particles; Particulate processes; Rheology; Stability

Nanomilling: the influence of suspension stability - Peukert, Wolfgang; Stenger, Frank (World Congress Particle Technology 4, 2002)
UnivIS-Import:2015-04-16:Pub.2002.tech.ITC.mechve.nanomi
Keywords: milling; stability

Nanoparticle Clustering in Supraparticles to Control Magnetic Long-Range Interactions - Wolf, Andreas; Zhou, Huanhuan; Groppe, Philipp; Stiegler, Lisa; Kämäräinen, Tero; Peukert, Wolfgang; Walter, Johannes; Wintzheimer, Susanne; Mandel, Karl (Particle & Particle Systems Characterization, 2024)
To tailor superparamagnetic iron oxide nanoparticles (SPIONs) to the specific needs of diverse application fields, it is essential to understand not only their intrinsic properties but also their interactions with each other. Theoretical models predicting/explaining the magnetization behavior of macroscopic samples containing millions of SPIONs are intricate due to the complexity of the underlying relaxation mechanisms in alternating fields. This study introduces supraparticles (SPs) as model architectures to empirically investigate magnetic interactions within and between large SPION clusters (>100 nanoparticles (NPs)). For this purpose, NP dispersions containing SPIONs and silica (SiO2)NPs as non-magnetic building blocks are spray-dried to form binary SPs. Selective salt-induced agglomeration of the two building block types before spray-drying is utilized to tailor SP architectures, including control over SPION cluster size, shape, and proximity. Magnetic particle spectroscopy (MPS), operating under ambient conditions, reveals altered magnetization behavior for different cluster structures. Not only the nearest SPION neighbors, but the whole cluster structure up to several micrometers is decisive for the magnetization behavior. This highlights the importance of long-range magnetic interactions. This work presents a versatile approach for designing model architectures to advance empirical interaction studies between SPIONs in macroscopic samples.
Created from Fastlane, Scopus look-up
Keywords: magnetic interactions; magnetic particle spectroscopy; selective agglomeration; spray-drying; superparamagnetic iron oxide nanoparticles; supraparticles

Nanoparticle precipitation: Experimental investigation, modelling and process simulation - Peukert, Wolfgang; Schwarzer, Hans-Christoph (European Congress on Crystallization, 2003)
UnivIS-Import:2015-04-16:Pub.2003.tech.ITC.mechve.nanopa
Keywords: simulation; nanoparticle

Nanoparticle precipitation in a T-mixer: Coupling experimentaland numerical investigations of the fluid dynamics with the solid formation processes - Peukert, Wolfgang; Gradl, Johannes; Schwertfirm, Florian; Schwarzer, Hans-Christoph; Schmid, Hans-Joachim; Manhart, Michael (ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering, 2006)
Mixing and consequently fluid dynamic is a key parameter to tailor the particle size distribution (PSD) in nanoparticle precipitation. Due to fast and intensive mixing a static T-mixer configuration is capable .for synthesizing continuously nanoparticles. The flow and concentration field of the applied mixer is investigated experimentally at different flow rates by Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF). Due to the PIV measurements the flow field in the mixer was characterized qualitatively and the mixing process itself is quantified by the subsequent LIF-measurements. A special feature of the LIF set up is to detect structures in the flow field, which are smaller than the Batchelor length. Thereby a detailed insight into the mixing process in a static T-Mixer is given. In this study a CFD-based approach using Direct Numerical Simulation (DNS) in combination with the solid formation kinetics solving population balance equations (PBE) is applied, using barium sulfate as modeling material. A Lagrangian Particle Tracking strategy is used to couple the flow field information with a micro mixing model and with the classical theory of nucleation. We found that the DNS-PBE approach including macro and micro mixing, combined with the population balance is capable of predicting the full PSD in nanoparticle precipitation for different operating parameters. Additionally to the resulting PSD, this approach delivers a 3D-information about all running subprocesses in the mixer, i.e. supersaturation built-up or nucleation, which is visualized for different process variables. Copyright © 2006 by ASME.
Keywords: mixing; fluid; dynamic; nanoparticle; precipitation

Nanoparticle production with stirred-media mills: Opportunities and limits - Knieke, Catharina; Carola, Steinborn; Romeis, Stefan; Peukert, Wolfgang; Breitung-Faes, Sandra; Kwade, Arno (Chemical Engineering & Technology, 2010)
Nanoparticles can be produced by wet grinding in stirred-media mills. In the lower nanometer range a true grinding limit exists, where the transferred energy from the grinding media is no longer sufficient to induce further breakage of the particles even after stressing events with high stress energies. Variations in process conditions lead to the conclusion that the grinding limit is hardly affected by most of the investigated process parameters. However, at high solids concentrations and/or small particle sizes, a drastic increase in suspension viscosity occurs, which leads to a dampening of the grinding media motion and to a reduction in the transferred stress energy. Hence, the rheological behavior can limit the grinding process, and a viscous dampening-related grinding limit can be reached prior to the true grinding limit. © 2010 WILEY-VCH Verlag GmbH & Co.
Keywords: Grinding limit; Nanoparticles; Rheology; Stirred-media mill; Ultrafine grinding

Nanoplasmonic Sensing for Monitoring the Initial Stages of Atmospheric Corrosion of Cu Nanodisks and Thin Films - Hosseinpour, Saman (Journal of The Electrochemical Society, 2013)

Nanoscale Patterning of Solid-Supported Membranes by Integrated Diffusion Barriers - Vogel, Nicolas; et al. (Langmuir, 2011)
Ultraflat nanostructured substrates have been used as a template to create patterned solid-supported bilayer membranes with polymerizable tethered lipids acting as diffusion barriers. Patterns in the size range of 100 nm were successfully produced and characterized. The diffusion barriers were embedded directly into the phospholipid bilayer and could be used to control the fluidity of the membrane as well as to construct isolated membrane corrals. By using nanosphere lithography to structure the templates it was possible to systematically adjust the lipid diffusion coefficients in a range comparable to those observed in cellular membranes. Single colloids applied as mask in the patterning process yielded substrates for creation of isolated fluid membrane patches corralled by diffusion barriers. Numerous potential applications for this new model system can be envisioned, ranging from the study of cellular interactions or of molecular diffusion in confined geometries to biosensor arrays.

Nature-inspired functional porous materials for low-concentration biomarker detection - Papiano, Irene; De Zio, Simona; Hofer, André; Malferrari, Marco; Minguez Bacho, Ignacio; Bachmann, Julien; Rapino, Stefania; Vogel, Nicolas; Magnabosco, Giulia (Materials Horizons, 2023)
sol-gel processes is a key challenge for their application as electrode materials. In this work, colloidal assembly, atomic layer deposition and selective surface functionalization are combined to design conductive inverse opals as an electrode material for novel glucose sensing platforms. An insulating inverse opal scaffold is coated with uniform layers of conducting aluminum zinc oxide and platinum, and subsequently functionalized with glucose oxidase embedded in a polypyrrole layer. The final device can sense glucose at concentrations in the nanomolar range and is not affected by the presence of common interferents gluconolactone and pyruvate. This method may also be applied to different conductive materials and enzymes to generate a new class of highly efficient biosensors.

Neues Verfahren zur Handhabung feinster Partikel und Herstellung dünner Schichten am Beispiel der Pulverlackierung mit Flüssigstickstoff - Wirth, Karl-Ernst; Nagel, Johannes; Molerus, Otto (Chemie Ingenieur Technik, 1998)
e Lackindustrie ist ein Industriezweig, der sehr stark gesetzlichen Reglementierungen unterliegt. Die immer strenger werdenden Auflagen im Bereich der Losemittelemission zwangen  die  betroffene  Industrie,  losemittelreduzierte Lacksysteme herzustellen und zu verarbeiten [l]. Die Herstellung solcher Systeme kann auf zwei Wege geschehen: - Reduktion des Losemittels, - Austausch des Losemittels durch Wasser bzw. Luft. Der Weg  der Losemittelreduktion fuhrt von den konventionellen  Lacksysteme  mit  einem Festkorpergehalt von ca. 50 bis 55 Ma.-% zu den Medium-Solid-  bm High- Solid-Lacksystemen mit einem Festkorpergehalt von ca. 55 bis 65 % bzw 65 bis 75 %. Durch Austausch des Losemittels gelangt man zu den Wasserlack- bzw. Pulverlacksystemen. Wasserlacksysteme  weisen je nach Anwendungsfall  einen Anteil organischer  Losemittel von 5 bis 20 Ma.-% auf. Die Pulverlacke hingegen  sind frei von  organischen  Losemitteln. Im Gegensatz  zu  den Flussiglacken  (konventionelle, Medium- und High-Solid-Lacksysteme  sowie Wasserlacke) lafit sich das Overspray der Pulverlacke zu nahezu 100 % recyclen. Die Losemittelfreiheit  und ein nahezu 100 %iges Recycling des Oversprays sind Griinde, die fir den immer starkeren Einsatz von Pulverlacken sprechen. Bisher wird der in Abb. 1 dargestellte Aufbau der elektrostatischen Pulverbeschichtung  (EPS) venvendet. Er besteht im wesentlichen aus einem Vorratsbehalter, der als Wirbelschicht aus- gefuhrt ist, einem Injektor, einer Forderleitung,  einer Pulverpistole mit einer Vorrichtung zur elektrostatischen Aufladung der Pulverlackpartikel und dem zu beschichtenden Objekt, das geerdet ist. Im vorliegenden Fall erfolgt die Aufladung der Pulverlackpartikel durch freie Ionen und Elek- tronen, die durch eine Corona-Entladung erzeugt werden. Ublichenveise werden mit  der EPS Pulverlacke verarbeitet,  deren KorngroRenverteilung  von 0 bis 80 pm reicht,  wobei  der Feinanteil  des  Pulverlacks  nur yxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA3 bis 8 Gew. -% kleiner 8 pmbetragt. ZumErzielen eines guten Glanz- grads sind nach Abb. 2 Schichtstarkenvon ca. 60 bis 70 pmzu applizieren. Die Angabe der Schichtstarke bezieht sich auf die Dicke der Lackschicht im eingebrannte Zustand. Sol1 aus Kostengriinden die applizierte Lackschicht dunner sein, ist
UnivIS-Import:2015-03-05:Pub.1998.tech.ITC.mechve.neuesv_74
Keywords: lack; farben; pulver; beschichtung

New approaches towards production of polymer powders for selective laser beam melting of polymers - Schmidt, Jochen; Sachs, Marius; Fanselow, Stephanie; Wirth, Karl-Ernst; Peukert, Wolfgang (32nd International Conference of the Polymer Processing Society, PPS 2016, 2017)
Keywords: wet grinding; dry coating; downer reactor; melt emulsification; laser beam melting of polymers; polypropylene (PP); polybutylene terephthalate (PBT)

New approach towards production of optimized polymer powders for additive manufacturing - Peukert, Wolfgang; Schmidt, Jochen; Sachs, Marius; Fanselow, Stephanie; Wirth, Karl-Ernst (8th International Conference for Conveying and Handling of Particulate Solids (CHoPS2015), 2015)
Rapid prototyping gradually is transferred to additive manufacturing opening many new applications. Especially powder- And beam-based processes such as laser beam melting (LBM) of polymers are promising. Major requirements for good processability in LBM of polymers are good flowability and high packing density. Within this contribution a novel process route for the production of micron-sized LBM powders [1] is presented exemplarily for polybutylene terephthalate (PBT). Wet comminution of the polymer is the first process step. Product particles with x < 10 μm are readily obtained by wet grinding [2]. The ground PBT microparticles are rounded in a heated downer reactor in the second process step. To increase the flowability of the spherical polymer particles further nanoparticles are adhered to the particle surface [3] in the third step. Spherical PBT microparticles of good flowability are obtained.
Keywords: powder; polymer; laser; beam; melting

New Insights Into Application Relevant Properties of Cu2+-Doped Brushite Cements - Späth, Karla; Nawaz, Qaisar; Schilling, Tatjana; Götz-Neunhoeffer, Friedlinde; Detsch, Rainer; Boccaccini, Aldo R.; Hurle, Katrin (Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2024)
Doping of brushite cements with metal ions can entail many positive effects on biological and physicochemical properties. Cu2+ ions are known to exhibit antibacterial properties and can additionally have different positive effects on cells as trace elements, whereas high Cu2+ concentrations are cytotoxic. For therapeutical applications of bone cement, a combination of good biocompatibility and sufficient mechanical properties is required. Therefore, the aim of this study was to investigate different physicochemical and biological aspects, relevant for application, of a brushite cement with Cu2+-doped β-tricalcium phosphate, monocalcium phosphate monohydrate and phytic acid as setting retarder. Additionally, the ion release was compared with a cement with citric acid as setting retarder. The investigated cements showed good injectability coefficients, as well as compressive strength values sufficient for application. Furthermore, no antibacterial effects were detected irrespective of the Cu2+ concentration or the bacterial strain. The cell experiments with eluate samples showed that the viability of MC3T3-E1 cells tended to decrease with increasing Cu2+ concentration in the cement. It is suggested that these biological responses are caused by the difference in the Cu2+ release from the hardened cement depending on the solvent medium. Furthermore, the cements showed a steady release of Cu2+ ions to a lesser extent in comparison with a cement with citric acid as setting retarder, where a burst release of Cu2+ was observed. In conclusion, despite the anticipated antibacterial effect of Cu2+-doped cements was lacking and mammalian cell viability was slightly affected, Cu2+-concentrations maintained the physicochemical properties as well as the compressive strength of cements and the slow ion release from cements produced with phytic acid is considered advantageous compared to citric acid-based formulations.
CRIS-Team Scopus Importer:2024-09-13
Keywords: antibacterial properties; copper; cytotoxicity; ion doping; β-tricalcium phosphate

New insights into colloidal gold flakes: structural investigation, micro-ellipsometry and thinning procedure towards ultrathin monocrystalline layers - Hoffmann, B.; Bashouti, M. Y.; Feichtner, Thorsten; Mackovic, Mirza; Dieker, Christel; Salaheldin, A. M.; Richter, P.; Gordan, O. D.; Zahn, D. R. T.; Spiecker, Erdmann; Christiansen, S.; Hoffmann, Björn (Nanoscale, 2016)
High-quality fabrication of plasmonic devices often relies on wet-chemically grown ultraflat, presumably single-crystalline gold flakes due to their superior materials properties. However, important details about their intrinsic structure and their optical properties are not well understood yet. In this study, we present a synthesis routine for large flakes with diameters of up to 70 mu m and an in-depth investigation of their structural and optical properties. The flakes are precisely analyzed by transmission electron microscopy, electron backscatter diffraction and micro-ellipsometry. We found new evidence for the existence of twins extending parallel to the Au flake 111 surfaces which have been found to not interfere with the presented nanopatterning. Micro-Ellipsometry was carried out to determine the complex dielectric function and to compare it to previous measurements of bulk single crystalline gold. Finally, we used focused ion beam milling to prepare smooth crystalline layers and high-quality nanostructures with desired thickness down to 10 nm to demonstrate the outstanding properties of the flakes. Our findings support the plasmonics and nano optics community with a better understanding of this material which is ideally suited for superior plasmonic nanostructures.

New possibilities of accurate particle characterisation by applying direct boundary models to analytical centrifugation - Walter, Johannes; Thajudeen, Thaseem; Süß, Sebastian; Segets, Doris; Peukert, Wolfgang (Nanoscale, 2015)
Analytical centrifugation (AC) is a powerful technique for the characterisation of nanoparticles in colloidal systems. As a direct and absolute technique it requires no calibration or measurements of standards. Moreover, it offers simple experimental design and handling, high sample throughput as well as moderate investment costs. However, the full potential of AC for nanoparticle size analysis requires the development of powerful data analysis techniques. In this study we show how the application of direct boundary models to AC data opens up new possibilities in particle characterisation. An accurate analysis method, successfully applied to sedimentation data obtained by analytical ultracentrifugation (AUC) in the past, was used for the first time in analysing AC data. Unlike traditional data evaluation routines for AC using a designated number of radial positions or scans, direct boundary models consider the complete sedimentation boundary, which results in significantly better statistics. We demonstrate that meniscus fitting, as well as the correction of radius and time invariant noise significantly improves the signal-to-noise ratio and prevents the occurrence of false positives due to optical artefacts. Moreover, hydrodynamic non-ideality can be assessed by the residuals obtained from the analysis. The sedimentation coefficient distributions obtained by AC are in excellent agreement with the results from AUC. Brownian dynamics simulations were used to generate numerical sedimentation data to study the influence of diffusion on the obtained distributions. Our approach is further validated using polystyrene and silica nanoparticles. In particular, we demonstrate the strength of AC for analysing multimodal distributions by means of gold nanoparticles.

New Prospects for Particle Characterization Using Analytical Centrifugation with Sector-Shaped Centerpieces - Uttinger, Maximilian; Boldt, Sebastian; Wawra, Simon; Freiwald, Tobias; Damm, Cornelia; Walter, Johannes; Lerche, Dietmar; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2020)
Analytical centrifugation (AC) has recently shown great potential for the accurate determination of particle size distributions. The well-established LUMiSizer(R) is customized by a new design allowing for higher rotor speeds, improved thermal insulation, and measurement cell assembly. The latter enables sedimentation analysis of nanoparticles (NPs) in sector-shaped centerpieces. The measurement window of AC experiments is assessed by the Peclet (Pe) number. It is shown that at low Pe numbers (0.7 < Pe < 30), sedimentation, and diffusion can be accurately and simultaneously analyzed from the sedimentation boundaries within one experiment. Moreover, sedimentation properties can be reliably determined up to Pe numbers of 4000. The thermal characteristic throughout the sedimentation analysis is validated by measuring polystyrene particles at elevated temperatures. Moreover, the performance of the setup is demonstrated by determining the sedimentation properties of SiO2 NPs at intermediate Pe numbers in excellent agreement with results from analytical ultracentrifugation experiments. Finally, for the first time, an accurate analysis of the core–shell properties of Au NPs via AC is presented. By combining the analysis of sedimentation and diffusional properties at low Pe numbers, the shell thickness of the stabilizer cetyltrimethylammonium bromide alongside the core diameter distribution of the Au NPs is determined.
CRIS-Team Scopus Importer:2020-06-19
Keywords: analytical centrifugation; core–shell nanoparticles; layering effects; nanoparticle characterization; sedimentation analysis

n-Hexanol Enhances the Cetyltrimethylammonium Bromide Stabilization of Small Gold Nanoparticles and Promotes the Growth of Gold Nanorods - Schmutzler, Tilo; Schindler, Torben; Zech, Tobias; Lages, Sebastian; Thoma, Martin; Appavou, Marie-Sousai; Peukert, Wolfgang; Spiecker, Erdmann; Unruh, Tobias (ACS Applied Nano Materials, 2019)
Gold nanorods (AuNRs) are of interest for many applications, since their absorption in the regime of visible light can easily be tuned by their exact shape. To produce these AuNRs, a two-step synthesis that starts from small seed particles is used. These seed particles are stabilized by cetyltrimethyl-ammonium bromide (CTAB), which forms micelles at the used concentration (0.1 mol/L). In this work, the influence of the micelle morphology on the stabilization of these seed particles and the consequences on the formation of AuNRs is reported. The elongation of CTAB micelles by the addition of n-hexanol leads to much more stable seed particle dispersions and thus less polydisperse AuNRs. In contrast, a higher number of micelles compared to pure CTAB dispersions result from the addition of n-pentanol. This promotes the formation of larger seed particles and leads to lower yields of AuNRs. The gold nanoparticles are characterized by UV-vis-NIR absorption spectroscopy, transmission electron microscopy, and small-angle X-ray scattering (SAXS). The morphology of the micelles has been determined by a combination of SAXS and small-angle neutron scattering (SANS). The experimental results were used to calculate the collision kinetics of seed particles by using an improved approach of classical coagulation theory to consider the anisotropy of the micelles. The combination of these experiments with the calculations strongly supports the mechanistic model-that these gold seed particles are not stabilized by a CTAB bilayer but by the micelles itself. For the first time, the influence of the micellar size and shape on the stabilization mechanism of noble metal nanoparticles could be clarified. Theses findings contribute to the development of targeted design routes for distinct nanoparticle morphologies by the use of suitable dispersions.
CRIS-Team WoS Importer:2019-06-18

N-Methyl-2-pyrrolidone as a Reaction Medium for Gold(III)-Ion Reduction and Star-like Gold Nanostructure Formation - Mirdamadi Esfahani, Maleknaz; Görlitzer, Eric; Kunz, Ulrike; Vogel, Nicolas; Engstler, Joerg; Andrieu-Brunsen, Annette (ACS Omega, 2022)
The efficiency of a wet chemical route to synthesize gold nanostructures with tunable size and shape significantly depends on the applied solvent and the interaction of solvent molecules with other species such as gold ions. The ability of the organic solvent N-methyl-2-pyrrolidone (NMP) as a suitable medium for application in star-like gold nanostructure (AuNS) synthesis with a tunable morphology at ambient conditions has been investigated. The time-dependent analysis of the UV-vis absorption spectra of AuIIICl4- in a pure NMP solution illustrates the role of NMP as simultaneous complexing and reducing agents. Kinetic studies indicate that AuIIICl4- in NMP solution is reduced to AuICl2-, with no need to use another reducing agent, any external energy sources, or solvent pretreatment. This is because AuI species stay stable in this solution unless poly(vinylpyrrolidone) (PVP) catalyzes their disproportionation. Morphological studies by transmission electron microscopy (TEM) specify the high-yield synthesis of AuNS with monocrystalline spikes in a concentrated NMP solution by PVP. This study illustrates that the presence of seeds, as another agent to catalyze the disproportionation of AuI species, makes it possible to synthesize AuNS in varying concentrations of PVP in this medium. The role of PVP concentration and the presence of seeds in the formation kinetics, morphology, and optical properties is systematically discussed. The results achieved through this study develop a straightforward and safe procedure for AuNS synthesis in high yield in a water-miscible organic polar solvent with tunable morphology and optical properties. Considering the high capability of NMP to dissolve various types of polymers and hydrophobic ligands, synthesizing AuNS in this solvent opens a window to a practical and easy way to fabricate gold-based nanomaterials with fascinating optical properties.
Created from Fastlane, Scopus look-up

NOBF4-Functionalized Au-Fe3O4 Nanoheterodimers for Radiation Therapy: Synergy Effect Due to Simultaneous Reactive Oxygen and Nitrogen Species Formation - Klein, Stefanie; Harreiß, Christina; Menter, Christina; Hümmer, Julian; Distel, Luitpold; Meyer, Karsten; Hock, Rainer; Kryschi, Carola (ACS Applied Materials and Interfaces, 2018)
Snowman-shaped Au-Fe3O4 nanoheterodimers were synthesized by thermal decomposition of iron oleate on presynthesized Au nanoparticles. Subsequently performed ligand exchange with nitrosyl tetrafluoroborate provided water solubility and enabled X-ray-induced NO release. These Au-Fe3O4 nanoheterodimers combine high-Z material with catalytically active Fe3O4 surfaces and, moreover, plasmonic properties with superparamagnetic performance. We could establish synergetic interactions between X-radiation and both the Au and Fe3O4 surfaces, which resulted in the simultaneous production of the nitric oxide radical at the Fe3O4 surface and the superoxide radical at the Au surface. The surface-confined reaction between these radicals generated peroxynitrite. This highly reactive species may cause nitration of mitochondrial proteins and lipid peroxidation and induce DNA strand breaks. Therefore, high concentrations of peroxynitrite are expected to give rise to severe cellular energetic derangements and thereupon entail rapid cell death. As providing a common platform for X-ray-induced formation of the highly superoxide, and peroxynitrite, nitrosyl tetrafluoroborate functionalized Au-Fe3O4 nanosnowmen were shown to exhibit excellent performance as X-ray-enhancing agents in radiation therapy.
Keywords: Au-Fe3O4 nanoheterodimers; nitrosyl tetrafluoroborate coating; radiation therapy; reactive oxygen species; reactive nitrogen species

Noble-Metal-Free Photocatalytic Hydrogen Evolution Activity: The Impact of Ball Milling Anatase Nanopowders with TiH2 - Zhou, Xuemei; Liu, Ning; Schmidt, Jochen; Kahnt, Axel; Osvet, Andres; Romeis, Stefan; Zolnhofer, Eva; Marthala, Venkata; Guldi, Dirk Michael; Peukert, Wolfgang; Hartmann, Martin; Meyer, Karsten; et al. (Advanced Materials, 2016)
Ball milling TiO2 anatase together with TiH2 can create an effective photocatalyst. The process changes the lattice and electronic structure of anatase. Lattice deformation created by mechanical impact combined with hydride incorporation yield electronic gap-states close to the conduction band of anatase. These provide longer lifetimes of photogenerated charge carriers and lead to an intrinsic cocatalytic activation of anatase for H2 evolution.
Keywords: Anatase; Ball milling; Hydrogen evolution; Photocatalysis; Titanium hydride

Non-invasive investigation of the cross-sectional solids distribution in CFB risers by X-ray computed tomography - Hensler, Timo; Firsching, Markus; Gomez Bonilla, Juan Sebastian; Woerlein, Thorsten; Uhlmann, Norman; Wirth, Karl-Ernst (Powder Technology, 2016)
We apply X-ray computed tomography for non-invasive investigation of the distribution of solids over the cross-section of a pilot plant scale circulating fluidized bed riser and present a novel method to derive volumetric solids concentrations from tomographic raw data. In this, the elimination of low-energetic radiation from the incident X-ray spectrum plays an essential role to avoid detrimental beam hardening effects, which are caused by the pipe material and the fluidized solids. The presented technique is applied for quantitative analysis of the radial solids concentration distribution in a gas-solid circulating fluidized bed riser. The examined operating range covers mean solids concentrations between 2.7 vol% and 37.2 vol% whilst the superficial gas velocity is varied between 1.5 m s-1 and 6.0 m s-1. The high spatial resolution of the measured data permits evaluation of the influence of the overall solids holdup and the superficial gas velocity on the radial solids concentration profile. Comparison of the cross-section averaged solids concentrations obtained by X-ray computed tomography with those inferred from differential pressure measurements confirms the high accuracy of the applied method. Based on a comprehensive set of measurement data a model is developed that allows for the prediction of the radial solids concentration distribution in vertical gas-solid upflow.
EAM Import::2019-03-08

Nonlinear spectroscopy meets particle interfaces: Revealing the interfacial structure of colloids - Sauerbeck, Christian; Schürer, Benedikt; Braunschweig, Björn; Peukert, Wolfgang (2012)

Novel acridone-modified MCM-41 type silica: Synthesis, characterization and fluorescence tuning - Zhou, Zhou; Klupp Taylor, Robin; et al. (Beilstein Journal of Nanotechnology, 2011)
Keywords: Fluorescence; Mcm-41; Acridone; Co-condensation; Scandium

Novel approaches for the production of polymer powders for selective laser beam melting of polymers - Schmidt, Jochen; Sachs, Marius; Fanselow, Stephanie; Wirth, Karl-Ernst; Peukert, Wolfgang (Solid Freeform Fabrication 2016: Proceedings of the 26th Annual International Solid Freeform Fabrication Symposium – An Additive Manufacturing Conference, 2016)
The opening of new fields of application of powder-based additive manufacturing methods like selective laser beam melting of polymers currently is hindered by the limited availability of materials showing good processability. So far, virtually only polyamides are available as optimized powder materials. Two innovative methods for production of spherical polymer micro particles for selective laser melting are discussed: The first approach, stirred media milling and rounding, is applicable for a variety of polymers. It will be exemplarily discussed for polyesters and the dependency of product properties (particle size distribution, shape, crystallinity) on the process parameters in the comminution and in the rounding step will be assessed. The second method, melt emulsification, will be demonstrated for polypropylene. Moreover, the possibilities of dry coating to tailor particle properties are illustrated. The influence of powder properties on the processability and on the quality of the obtained devices is outlined.<br
Keywords: AdditivesCrystallinityEmulsificationLaser beamsMeltingParticle sizeParticle size analysisPolypropylenes Selective Laser Sintering; Nylon 12; Polybutylene Terephthalate; Innovative method; Laser beam melting; Particle properties; Polymer powders; Powder properties; Process parameters; Product property; Spherical polymers; Selective laser melting

Novel concepts for characterisation of heterogeneous particulate surfaces - Peukert, Wolfgang; Mehler, Carsten; Götzinger, Martin (Applied Surface Science, 2002)
Surface properties of fine particles are of high relevance in several technical applications, such as nanotechnology, adsorption or crystallisation. Particulate surfaces are not well-defined, may contain flaws and dislocations, internal stresses and all kinds of impurities. Thus, these surfaces are structurally and energetically heterogeneous. Their interactions are, therefore, poorly understood. Adsorption equilibria, adhesion forces or contact angles reflect the interaction of molecules and particles with surfaces and fluid phases. Modelling of these elementary processes leads to mean or distributed surface properties of technical surfaces and small particles. The dispersive interactions of heterogeneous surfaces are characterised by mean parameters like a Hamaker constant. Henry coefficients of gases on activated carbon, graphite and alumina have been quantitatively described as a function of the critical temperature and pressure of the respective adsorptive and the Hamaker constant of the solid. Conversely, Hamaker constants determined from adsorption experiments are used to predict measured adhesion forces of alumina particles. Polar interactions are described by a new approach derived from continuum models of liquids. The particle surface is characterised by a density distribution of partial charges on small surface patches. By means of a statistical mechanical approach Henry coefficients both in the gas and liquid phase can be described quantitativel
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.novelc_8
Keywords: Particle surfaces; Characterisation; Adsorption; Adhesion

Novel Concepts for Teaching Particle Technology - Peukert, Wolfgang; Schmid, Hans-Joachim (Chemical Engineering Education, 2002)
The introduction of particle technology in chemical engineering is discussed. The course focuses on product property approach. The course enhances the students's awareness of the whole process, the concepts for the formation of structured solids, product design and powder processing systems. Another course on particle characterization enables the students to choose an appropriate setup for arbitrary particle characterization task.
UnivIS-Import:2015-03-09:Pub.2002.tech.ITC.mechve.novelc
Keywords: teaching; perticle; technology

Novel luminescent composite polymer fibers for warning and security systems - Peukert, Wolfgang; Damm, Cornelia; Schäfer, Karola; Möller, Martin; Gries, Thomas; Wang, Hailin; Pich, Andrij; Wilms, Christian; Seide, Gunnaer (Technische Textilien, 2012)
Novel luminescent, inorganic and organic nanopigments were developed for the preparation of polyethylene terephthalate (PET) fibers for applications in warning and security textiles. Luminescent nanopigments were designed by bottom-up procedures using precipitation synthesis or by top-down procedures using reactive grinding processes. The investigated nanopigments were zinc sulfide, doped with copper or manganese and strontium aluminate, doped with europium and dysprosium. Furthermore, organic dyestuffs and pigments (aldazines or perylenes) were investigated, some of them after encapsulation into silica nanoparticles. The obtained nanoparticles were applied to polymer melts for the production of filaments by extrusion processes. For this, the nanopigments were incorporated into masterbatches or liquid formulations. The filaments were finally investigated in texturing processes and were then further processed to textile fabrics. By usage of nanoscale luminescent pigments, higher luminescence, lower pigment dosage combined with better light, heat and wet fastness were achieved compared to conventionally used systems.
Keywords: luminiscent; polymer; nanopigment; precipitation; fiber

Novel luminescent composite polymer fibers for warning and security systems - Schäfer, Karola; Wang, Hailin; Pich, Andrij; Mol̈ler, Martin; Damm, Cornelia; Peukert, Wolfgang; Wilms, Christian; Seide, Gunnar; Gries, Thomas (Chemical Fibers International, 2012)
Conventional warning and security textiles based on molecular dispersed luminescent dyes exhibit limited photostability and wet fastness. The washing resistance of the textiles can be improved by using luminescent pigments instead of dyes for their coloration. The idea is to use the liquid agent for dispersion of the highly luminescent particles in this medium. The whole system is then injected into the extruder of the spin- fling unit and fibers are formed. The liquid agent stays inside the polymer and, therefore, has to be compatible with the polymer in order to avoid negative impact on the mechanical properties of the fibers. The evaluation of the dependence of changes of the properties and the process conditions is ambiguous, since the particle content and the amount of liquid dispersion agent was changed at the same time.
Keywords: textile; luminescent; dye; photostability; disperion; particle; extrusion

Novel process routes towards the production of spherical polymer powders for selective laser sintering - Schmidt, Jochen; Dechet, Maximilian; Gomez Bonilla, Juan Sebastian; Kloos, Stephanie; Wirth, Karl-Ernst; Peukert, Wolfgang (AIP Conference Proceedings, 2019)
Additive manufacturing processes allow the production of individualized and complex parts without the use of molds or tools. Especially powder and beam-based AM processes like selective laser sintering (SLS) of polymers are promising, although the choice of commercial SLS powders is very limited. To further extend the applications of SLS, new and cheap materials with good processability must be supplied. Within this contribution two innovative methods for production of spherical polymer micro particles for SLS are discussed: The first approach is a process chain applicable to a wide range of polymers consisting of wet grinding in a stirred media mill followed by rounding of the obtained irregularshaped particles in a heated downer reactor and subsequent dry coating of the spherical particles for improvement of powder flowability. It will be outlined for glass-filled PBT systems. The second approach is melt emulsification with subsequent dry coating. In this process a polymer melt is emulsified by elongational and shear stresses in a rotor stator device. The method is exemplified for polypropylene (PP). Both approaches allow for production of spherical polymer micro particles. The effect of flowability, shape and bulk density on the powders' processabilities in SLS is assessed.
CRIS-Team Scopus Importer:2019-10-22
Keywords: Additive manufacturing; Melt emulsification; Polymer powder; Rounding

Nucleation as a rate-determining step in catalytic gas generation reactions from liquid phase systems - Solymosi, Thomas; Geißelbrecht, Michael; Mayer, Sophie; Auer, Michael; Leicht, Peter; Terlinden, Markus; Malgaretti, Paolo; Bösmann, Andreas; Preuster, Patrick; Harting, Jens; Thommes, Matthias; Vogel, Nicolas; et al. (Science Advances, 2022)
The observable reaction rate of heterogeneously catalyzed reactions is known to be limited either by the intrinsic kinetics of the catalytic transformation or by the rate of pore and/or film diffusion. Here, we show that in gas generation reactions from liquid reactants, the nucleation of gas bubbles in the catalyst pore structure represents an additional important rate-limiting step. This is highlighted for the example of catalytic hydrogen release from the liquid organic hydrogen carrier compound perhydro-dibenzyltoluene. A nucleation-inhibited catalytic system produces only dissolved hydrogen with fast saturation of the fluid phase around the active site, while bubble formation enhances mass transfer by more than a factor of 50 in an oscillating reaction regime. Nucleation can be efficiently triggered not only by temperature changes and catalyst surface modification but also by a mechanical stimulus. Our work sheds new light on performance-limiting factors in reactions that are of highest relevance for the future green hydrogen economy.

Nucleotide passivated cadmium sulfide quantum dots - Green, Mark; Smyth-Boyle, David; Harries, Joanna; Klupp Taylor, Robin (Chemical Communications, 2005)
Semiconductor quantum dots are finding numerous applications in biological systems; in this paper, we report the simple in situ preparation of nucleotide capped cadmium sulfide (CdS) nanoparticles and investigate the interaction of the capping agent with the nanoparticle surfac
Keywords: particle; quantum; dots; functionalization

Numerical and experimental investigation of the turbulent flow and mixing in a static T-mixer - Peukert, Wolfgang; Schwertfirm, Florian; Manhart, Michael; Gradl, Johannes; Schwarzer, Hans-Christoph (ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering, 2006)
Turbulent mixing plays 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 two direct numerical simulations (DNS) of a confined impinging jet reactor (CIJR) at Re = 500 and Sc = 1, with and without modelling the feeding pipes. The data is compared with particle image velocimetry (PIV) measurements and it is shown that only the simulation which includes the feeding pipes gives the correct flow field. This flow field 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 and decrease rapidly towards the exit of the CIJR. In the whole CIJR the turbulence is not in equilibrium. The mixing of the scalar is rapid in the impingement zone, but due to the fast decrease of the turbulent intensities and due to the relaminarisation of the flow the PDFs of the scalar distributions in cross sections of the CIJR take a bimodal form after the impingement zone. Copyright © 2006 by ASME.
Keywords: turbulence; mixing; kinetic; energy; simulation; jet; impinging

Numerical Investigation of Flow Patterns and Concentration Profiles in Y-Mixers - Babu, Harsha Vardhan; Sahu, Swati; Haderlein, Michael; Peukert, Wolfgang; Verma, Nishith (Journal of Chemical Engineering & Process Technology, 2016)
The fluid flow patterns and associated concentration fields in Y-mixers are investi- gated using lattice Boltzmann method-based models. The focus lies on the impact of the mixing angle on the flow and concentration fields, with the mixing angle varying between acute (q =10) and obtuse (q = 130) angles. Residence time dis- tributions are determined to study the effect of the angles on the mixing and velocity patterns, in particular, different flow regimes, i.e., stratified laminar, vor- tex, and engulfment flow. The results from the simulations are validated with liter- ature data and found to be in good agreement. Maximum mixing occurs in the 100 obtuse-angle Y-mixer, attributed to the extensive engulfment of flows in the mixing channel.<br
Keywords: Lattice Boltzmann methods; Micromixers; Computational fluid dynamics; Residence time distribution; Y-mixers

Numerical methods for particle agglomeration and breakage in lid-driven cavity flows at low Reynolds numbers - Roy, N.; Dürr, R.; Bück, Andreas; Kumar, J.; Sundar, S. (Mathematics and Computers in Simulation, 2022)
In this paper, a rigorous computational study is carried out on the three numerical methods: cell average technique (CAT), weighted finite volume scheme (WFVS), and quadrature method of moments (QMOM). Each method is analyzed to solve the population balance equation coupled with hydrodynamics. Different test cases have been considered for aggregation, breakage, simultaneous aggregation and breakage processes with four different aggregation kernels and uniform breakage function. Both the advantages and disadvantages of those methods are thoroughly investigated for the PBE coupled with hydrodynamics. Based on accuracy and efficiency, it is recommended that the WFVS is a smart choice for computing number density and moments in the case of inhomogeneous PBE.
CRIS-Team Scopus Importer:2021-09-10
Keywords: Cell average technique; Lid-driven cavity; Multi-phase flow; Population balance equation; QMOM

NUMERICAL SOLUTIONS FOR MULTIDIMENSIONAL FRAGMENTATION PROBLEMS USING FINITE VOLUME METHODS - Saha, Jitraj; Das, Nilima; Kumar, Jitendra; Bück, Andreas (Kinetic and Related Models, 2019)
We introduce a finite volume scheme for approximating a general multidimensional fragmentation problem. The scheme estimates several physically significant moment functions with good accuracy, and is robust with respect to use of different nonuniform daughter distribution functions. Moreover, it possess simple mathematical formulation for defining in higher dimensions. The efficiency of the scheme is validated over several test problems.
CRIS-Team WoS Importer:2019-02-21

Numerical study of the hydrodynamics of fluidized beds operated under sub-atmospheric pressure - Zarekar, Sayali; Bück, Andreas; Jacob, Michael; Tsotsas, Evangelos (Chemical Engineering Journal, 2019)
Fluidized beds operated under partial vacuum offer a promising alternative to the expensive freeze-drying technique for processing thermo-sensitive materials in the food and pharmaceutical industries. However, the hydrodynamics of vacuum fluidized beds has not been extensively investigated. In this paper, we apply a two-fluid Eulerian model to investigate the influence of sub-atmospheric pressure on the hydrodynamic characteristics in two-dimensional fluidized beds. The simulations are compared with experiments performed in a batch vacuum fluidized bed plant. A parametric study of the effect of pressure on bed hydrodynamics is performed for two fluidization conditions: (1)constant excess velocity and (2)three times the minimum fluidization velocity. The pressure is varied in the range 1000 mbar–100 mbar with fluidized particles belonging to Geldart group D. A detailed investigation is carried out on porosity distribution, bed expansion, bypass ratio, and bubble characteristics. At low pressure, the porosity distribution is non-homogeneous with increased bubble activity near walls. A decrease in bed porosity and bubble splitting is observed as the operating pressure is reduced. The simulation results are also compared with semi-empirical correlations developed for atmospheric pressure conditions. The applicability of these correlations at sub-atmospheric pressures is, thus, evaluated.
CRIS-Team Scopus Importer:2019-05-14
Keywords: Bubble dynamics; CFD; Fluidized bed; Gas-solid flow; Reduced pressure; Vacuum

Numerical study of the packing density of fine powders by means of the Discrete Element Method - Blümel, Christina; Ribeiro Parteli, Eric Josef; Schmidt, Jochen; Wirth, Karl Ernst; Peukert, Wolfgang; Pöschel, Thorsten (85th Annual Meeting of the International Association of Applied Mathematics and Mechanics – GAMM 2014, 2014)
Numerical simulations by means of the Discrete Element Method (DEM) can provide a helpful tool in the investigation of the packing behavior of powders. In this type of numerical simulations, the Newton’s equations of motion for every single particle in the system are solved by taking into account all forces and torques acting on it, both due to external fields and due to interactions with other particles in the system

O2 adsorption dependent photoluminescence emission from metal oxide nanoparticles - Gheisi, Amirreza; Neygandhi, Chris; Sternig, Andreas; Carrasco, Esther; Marbach, Hubertus; Thomele, Daniel; Diwald, Oliver (Physical Chemistry Chemical Physics, 2014)
Optical properties of metal oxide nanoparticles are subject to synthesis related defects and impurities. Using photoluminescence spectroscopy and UV diffuse reflectance in conjunction with Auger electron spectroscopic surface analysis we investigated the effect of surface composition and oxygen adsorption on the photoluminescence properties of vapor phase grown ZnO and MgO nanoparticles. On hydroxylated MgO nanoparticles as a reference system, intense photoluminescence features exclusively originate from surface excitons, the radiative deactivation of which results in collisional quenching in an O2 atmosphere. Conversely, on as-prepared ZnO nanoparticles a broad yellow emission feature centered at h extgreeknEm = 2.1 eV exhibits an O2 induced intensity increase. Attributed to oxygen interstitials as recombination centers this enhancement effect originates from adsorbate-induced band bending, which is pertinent to the photoluminescence active region of the nanoparticles. Annealing induced trends in the optical properties of the two prototypical metal oxide nanoparticle systems, ZnO and MgO, are explained by changes in the surface composition and underline that particle surface and interface changes that result from handling and processing of nanoparticles critically affect luminescence.
EAM Import::2019-03-08

Observing Oriented Attachment during Mesocrystal Growth with in Situ Dynamic Light Scattering (DLS) - Embrechts, Heidemarie; Zhang, Siqi; Hock, Rainer; Peukert, Wolfgang; Distaso, Monica (Crystal Growth & Design, 2020)
Despite rapidly growing interest in the application of mesocrystals in catalysis, energy storage, and sensing, the understanding of mesocrystal formation mechanisms remains a relatively unexplored field, due to the time and space overlapping of different reaction steps, namely, the nucleation and growth of solid phase and, possibly, their self-assembly in 3D superstructures. In particular, the role of polymers used as templating matrices requires more in-depth investigation. Here, ZnO–PVP mesocrystals are used as a model system and their formation from molecular precursors is followed with simultaneous in situ dynamic light scattering (DLS) and turbidity measurements. The formation of 10 nm primary building blocks during the early stages of the synthesis and their subsequent oriented attachment into 200–1200 nm mesocrystalline superstructures are both directly observed with in situ DLS. The primary particle concentration at which oriented attachment (OA) begins to occur at an observable rate is proportional to the colloidal primary particle stability and is compared for different synthesis conditions with inline turbidity measurements. Synthesis with higher PVP concentrations and molecular weights results in increasingly sterically stabilized primary particles and the formation of larger ZnO–PVP mesospheres. The larger diameter of mesocrystals synthesized at higher PVP educt concentrations is attributed to partial screening of (electrostatic repulsive) interparticle interactions between mesocrystals and primary particles by attached surface PV
Keywords: Oxides; Nanoparticles; Dynamic light scattering; Chemical synthesis; Metal oxide nanoparticles

On-Demand Coupling of Electrically Generated Excitons with Surface Plasmons via Voltage-Controlled Emission Zone Position - Zakharko, Yuriy; Held, Martin; Sadafi, Fabrizio-Zagros; Gannott, Florentina; Mandavi, Ali; Peschel, Ulf; Klupp Taylor, Robin; Zaumseil, Jana (ACS Photonics, 2016)
The ability to confine and manipulate light below the diffraction limit is a major goal of future multifunctional optoelectronic/plasmonic systems. Here, we demonstrate the design and realization of a tunable and localized electrical source of excitons coupled to surface plasmons based on a polymer light emitting field-effect transistor (LEFET). Gold nanorods that are integrated into the channel support localized surface plasmons and serve as nanoantennas for enhanced electroluminescence. By precise spatial control of the near-infrared emission zone in the LEFET via the applied voltages the near-field coupling between electrically generated excitons and the nanorods can be turned on or off as visualized by a change of electroluminescence intensity. Numerical calculations and spectroscopic measurements corroborate significant local electroluminescence enhancement due to the high local density of photonic states in the vicinity of the gold nanorods. Importantly, the integration of plasmonic nanostructures hardly influences the electrical performance of the LEFETs, thus, highlighting their mutual compatibility in novel active plasmonic devices.
Keywords: surface plasmon polariton; organic semiconductor; field-effect transistor; electroluminescence; Purcell effect; active plasmonics

One-pot colloidal synthesis of plasmonic patchy particles - Bao, Huixin; Peukert, Wolfgang; Klupp Taylor, Robin (Advanced Materials, 2011)
The one-pot synthesis of patchy particles with morphologically tunable optical properties by the heterogeneous nucleation and growth of silver onto colloidal silica particles is described. Heat treatment of the silica and coating reaction conditions can be optimized in order to produce full yields of patchy particles. Dissolution of the cores leads to stable silver cages. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Keywords: asymmetric nanoparticles; colloids; core/shell nanoparticles; janus particles; silver

On Identifiability and Model Validation of a Population Balance Model for Liquid-Liquid-Mixing - Wilms, Terrance; Topalovic, Daniel; Bliatsiou, Chrysoula; Villwock, Jörn; Kraume, Matthias; Bück, Andreas; Knorn, Steffi (IFAC-PapersOnLine, 2025)
In this paper, liquid-liquid-mixer systems modelled by population balance equations are considered. As the control input / manipulated variable, the stirrer speed (and hence the energy dissipation rate) is used to control the distribution of the particle size. Three different measurement signals are considered. We investigate the observability and identifiability of the system for each measurement option and show that only in one scenario the model is observable and structurally identifiable. Further, it is shown that in this scenario, practical identifiability is generally challenging and particular care must be taken to ensure the model with identified parameter values is able to describe the dynamic behaviour of the system.
CRIS-Team Scopus Importer:2025-04-18
Keywords: Identifiability; Liquid/Liquid-Mixer Systems; Observability; Population Balance Equation Model; Process Control

Online Monitoring of Styrene Polymerization in Miniemulsion by Hyperpolarized (129)Xenon NMR Spectroscopy - Vogel, Nicolas; et al. (Macromolecules, 2012)
Online monitoring of a miniemulsion polymerization of styrene by hyperpolarized Xe-129 NMR spectroscopy is presented. The chemical shift of Xe-129 directly reports on the monomer/polymer ratio in the reaction mixture and therefore on the conversion of the reaction. The method allows for monitoring the progress of a polymerization with high time resolution and without sample extraction. The results obtained by Xe-129 NMR spectroscopy were successfully validated by comparison with results of calorimetry. Further characterization of the polymer dispersions with regard to the solids content and the particle diameters proved the comparability of both methods. Small deviations in the kinetic data and the properties of the polymer suspension from both methods are explained by the loss of monomer during the Xe-129 NMR experiments due to the used setup. In the future, Xe-129 NMR might also be applied for online monitoring of other chemicals reactions, e.g., allowing for determining the kinetics of thermoneutral reactions.

On the complex role of ammonia in the electroless deposition of curved silver patches on silica nanospheres - Sadafi, Fabrizio-Zagros; Sauerbeck, Christian; Braunschweig, Björn; Klupp Taylor, Robin (Crystengcomm, 2018)

On the control of dispersion interactions between biological membranes and protein coated biointerfaces - Blackwell, Robert; Hemmerle, Arnaud; Baer, Andreas; Späth, Matthias; Peukert, Wolfgang; Parsons, Drew; Sengupta, Kheya; Smith, Ana-Suncana (Journal of Colloid and Interface Science, 2021)
Hypothesis: Interaction of cellular membranes with biointerfaces is of vital importance for a number of medical devices and implants. Adhesiveness of these surfaces and cells is often regulated by depositing a layer of bovine serum albumin (BSA) or other protein coatings. However, anomalously large separations between phospholipid membranes and the biointerfaces in various conditions and buffers have been observed, which could not be understood using available theoretical arguments. Methods: Using the Lifshitz theory, we here evaluate the distance-dependent Hamaker coefficient describing the dispersion interaction between a biointerface and a membrane to understand the relative positioning of two surfaces. Our theoretical modeling is supported by experiments where the biointerface is represented by a glass substrate with deposited BSA and protein layers. These biointerfaces are allowed to interact with giant unilamellar vesicles decorated with polyethylene glycol (PEG) using PEG lipids to mimic cellular membranes and their pericellular coat. Results: We demonstrate that careful treatment of the van der Waals interactions is critical for explaining the lack of adhesiveness of the membranes with protein-decorated biointerfaces. We show that BSA alone indeed passivates the glass, but depositing an additional protein layer on the surface BSA, or producing multiple layers of proteins and BSA results in repulsive dispersion forces responsible for 100 nm large equilibrium separations between the two surfaces.
CRIS-Team Scopus Importer:2021-05-14
Keywords: Biointerfaces; Dispersion forces; Lifshitz theory; Reflection interference contrast microscopy (RICM); Van der Waals interactions

On the development of polymer particles for laser powder bed fusion via precipitation - Dechet, Maximilian; Schmidt, Jochen (Procedia CIRP, 2020)
In this contribution, some aspects of the development of powder bed fusion (PBF) feedstock powders via the solution-dissolution process, also known as precipitation, are exemplary addressed based on the authors' own work. The development is based on the selection of an appropriate polymer-solvent system, followed by the investigation of the cloud point diagram. After identification of a polymer-solvent system for precipitation, process-product relations, i.e. the influence of stirring, concentration and thermal regime on particle size distribution and shape, can be assessed. Via thorough product characterization concerning, amongst others, flowability and thermal properties, not only applicable PBF process parameters, but also necessary in-situ additive-enhancement with thermal stabilizers or post-processing with flow aids can be derived.
CRIS-Team Scopus Importer:2020-10-30
Keywords: Additive Manufacturing; Feedstock; Particles; Polymers; Powder bed fusion; Precipitation

On the dynamics and control of continuous fluidized bed layering granulation with screen-mill-cycle - Neugebauer, C.; Diez, E.; Bück, Andreas; Palis, S.; Heinrich, S.; Kienle, A. (Powder Technology, 2019)
This paper is concerned with an experimental and theoretical study of dynamics and control of fluidized bed layering granulation with external screen mill cycle. To achieve quantitative agreement between model calculations and experiments an extended dynamic process model is proposed. In contrast to previous work by Dreyschultze et al. [1] specific plant characteristics are taken explicitly into account including a more detailed model of the milling process and a classifying particle withdrawal from the granulation chamber. The model is then used to develop new control strategies. First, a novel bed mass controller is designed and validated. Afterward, a second control loop is introduced to dampen the oscillatory behavior of the particle size distribution. It is shown that the new control concepts achieve stable steady-state operation within a short time and thereby improve the process dynamics significantly. Theoretical predictions and experimental results are shown to be in good agreement.
CRIS-Team Scopus Importer:2019-07-12
Keywords: Continuous operation; Control; Fluidized bed layering; Stability

On the entangled growth of NaTaO3 cubes and Na2Ti3O7 wires in sodium hydroxide solution - Baumann, Stefan O.; Liu, Chang; Elser, Michael J.; Sternig, Andreas; Siedl, Nicolas; Berger, Thomas; Diwald, Oliver (Chemistry - A European Journal, 2013)
The entangled growth of sodium titanate Na2Ti3O7 nanowires and sodium tantalate NaTaO3 cubes was investigated with electron microscopy, X‐ray diffraction, and UV diffuse reflectance spectroscopy. Depending on the composition of the Ta2O5‐ and TiO2‐particle‐based powder mixtures, which served as educts, we observed different types of hybridization effects. These include the titanium‐induced contraction of the NaTaO3 perovskite‐type unit cell and the generation of electronic defect states in NaTaO3 that give rise to optical subbandgap transitions and tantalum‐induced limitations of the Na2Ti3O7 nanowire growth. The transformation from Ta2O5 to NaTaO3 occurs through a dissolution–recrystallization process. A systematic analysis of the impact of different titanium sources on NaTaO3 dispersion and, thus, on the properties of the entangled nanostructures revealed that a perfect intermixture of cubes and nanowires can only be achieved when titanate nanosheets emerge during transformation as reaction intermediates and shield nucleation and growth of isolated NaTaO3 cubes. The here demonstrated approach can be highly instrumental for understanding the nucleation and growth of composite and entangled nanostructures in solution and—at the same time—provides an interesting new class of photoactive composite material
Keywords: nanostructures; optical properties; crystal growth; doping; tantalum

On the impact of accessible surface and surface energy on particle formation and growth from the vapour phase - Peukert, Wolfgang; Artelt, Cordula; Schmid, Hans-Joachim (Journal of Aerosol Science, 2005)
This work investigates effects of reduced accessible surface area of aggregate particles and surface energy on titania particle formation and growth. It is taken into consideration that surface-related growth mechanisms, i.e. surface reaction and condensation, are limited to the fraction of the surface area of primary particles which is exposed to the collision with single molecules. Surface energy data determine the critical particle size with respect to evaporation and values are varied within the published range. This implies to develop a model which considers "surface shielding" and accounts for the formation of stable clusters from a supersaturated vapour due to nucleation and condensation besides considering the generation of monomers due to chemical reaction, growth due to surface reaction, agglomeration and sintering. Taking the accessible surface area into account is found out to be especially important if agglomerates contain a large number of primary particles or if agglomerate structure is rather compact. In this case, precursor consumption and primary particle growth turn out to be significantly retarded. Surface energy data are shown to be decisive with respect to the thermodynamic barrier to the formation of particles, thus to active particle formation and growth mechanisms, besides affecting sintering kinetics. Elevated surface energy data typically retard precursor consumption and favour primary particle growth. © 2004 Elsevier Ltd. All rights reserved.
Keywords: Accessible surface; Aerosol process simulations; Nanoparticles; Surface energy

On the Importance of Nanoparticle Necks and Carbon Impurities for Charge Trapping in TiO2 - Elser, Michael J.; Neige, Ellie; Berger, Thomas; Chiesa, Mario; Giamello, Elio; Mckenna, Keith; Risse, Thomas; Diwald, Oliver (Journal of Physical Chemistry C, 2023)
Particle attachment and neck formation inside TiO2 nanoparticle networks determine materials performance in sensing, photo-electrochemistry, and catalysis. Nanoparticle necks can feature point defects with potential impact on the separation and recombination of photogenerated charges. Here, we investigated with electron paramagnetic resonance a point defect that traps electrons and predominantly forms in aggregated TiO2 nano particle systems. The associated paramagnetic center resonates in the g factor range between g = 2.0018 and 2.0028. Structure characterization and electron paramagnetic resonance data suggest that during materials processing, the paramagnetic electron center accumulates in the region of nanoparticle necks, where O2 adsorption and condensation can occur at cryogenic temperatures. Complementary density functional theory calculations reveal that residual carbon atoms, which potentially originate from synthesis, can substitute oxygen ions in the anionic sublattice, where they trap one or two electrons that mainly localize at the carbon. Their emergence upon particle neck formation is explained by the synthesis-and/or processing-induced particle attachment and aggregation facilitating carbon atom incorporation into the lattice. This study represents a substantial advance in linking dopants, point defects, and their spectroscopic fingerprints to microstructural features of oxide nanomaterials.
CRIS-Team WoS Importer:2023-05-19

On the mechanism of Zn4O-acetate precursors ripening to ZnO: How dimerization is promoted by hydroxide incorporation - Segets, Doris; Milek, Theodor; Kirschbaum, Rolf; von Gernler, Marc; Lübbert, Christian; Drewello, Thomas; Peukert, Wolfgang; Zahn, Dirk (Journal of Chemical Physics, 2015)
We report on a combined experimental and molecular modelling study on Zn4O ion clusters stabilized by acetate molecules (OAc). In particular, ab initio calculations of acetate substitution by hydroxide ions are compared with mass spectrometry data. Though quantum calculations in the gas phase indicate strong energetic preference, no experimental evidence of stable Zn4O(OAc)6−x(OH)x clusters in ethanolic solutions could be observed. This apparent contradiction is rationalized by identifying the supportive role of hydroxide ions for the association of (OAc− → OH− substituted) Zn4O(OAc)6 and Zn4O(OAc)5+ clusters. Mass spectrometry and quantum calculations hint at the stability of (Zn4O)2(OAc)12−x(OH)x dimers with x = 1, 2. Therein, the hydroxide ions establish salt-bridges that allow for the formation of additional Zn3 motifs with the OH above the triangle center—a structural motif close to that of the ZnO-crystal. The association of Zn4O(OAc)6 clusters is thus suggested to involve OAc− → OH− substitution as an activation step, quickly followed by dimerization and the subsequent agglomeration of oligomer
Keywords: mechanism; particle; rod; nano; ripening

On the relevance of accounting for the evolution of the fractal dimension in aerosol process simulations - Peukert, Wolfgang; Artelt, Christian; Schmid, Hans-Joachim (Journal of Aerosol Science, 2003)
A population balance model is presented, which tracks particle growth in the gas phase and accounts for simultaneous agglomeration and sintering: Simulations reveal the evolution of the full distribution of a volume equivalent diameter and, amongst others, the evolution of the agglomerate collision diameter, a mean primary particle size and the number of primary particles per agglomerate. Furthermore, assuming fractal behaviour of the growing agglomerate particles—for the first time—a model for the evolution of a mean value of the fractal dimension based on physical and process parameters is proposed and incorporated into the simulation model. PARSIVAL, a commercial solver for integro-differential equations is employed to solve the equations involved. It is based on a generalised finite-element scheme with self-adaptive grid- and order construction. Calculations are performed to validate the model against monodisperse and sectional models published in literature for the exemplary case of Si production. The results are in good agreement if the same simplifying assumptions are made. However, results obtained from the new model for both—isothermal and non-isothermal process conditions—clearly show that it is important to consider the changing fractal dimension in many cases.
UnivIS-Import:2015-03-09:Pub.2003.tech.ITC.mechve.simula
Keywords: aerosol; agglomeration; simulation

On the Size-Determining Role of the Comonomer in the Nucleation and Growth of Cationic Polystyrene Latex via Emulsion Polymerization - Meincke, Thomas; Jordan, Maximilian; Vogel, Nicolas; Klupp Taylor, Robin (Macromolecular Chemistry and Physics, 2018)
Keywords: particle size; polystyrene; colloids; nucleation; cationic

Optical Analysis and Material Characterization of Nanoparticulate Oxides Synthesized via Flame Spray Pyrolysis - Münsterjohann, Bettina; Engel, Sascha; Stanzel, Melanie; Kilian, Daniel; Herre, Patrick; Peukert, Wolfgang; Will, Stefan (2014 MRS (Materials Research Society) Fall Meeting and Exhibit, 2014)

Optical Characterization of a Flame Spray Pyrolysis Process for the Synthesis of Nanoparticulate Oxides - Holfelder, Sandra; Stanzel, Melanie; Peukert, Wolfgang; Will, Stefan (36th International Symposium on Combustion, 2016)

Optical Investigation of a Flame Spray Pyrolysis Process for the Production of Nanoparticulate Oxides - Münsterjohann, Bettina; Holfelder, Sandra; Stanzel, Melanie; Peukert, Wolfgang; Will, Stefan (International Symposium Gas-phase Synthesis of Functional Nanomaterials, 2017)

Optical investigations of the droplet formation, evaporation and particle nucleation during the synthesis of zinc oxide nanoparticles in a Flame Spray Pyrolysis Process - Münsterjohann, Bettina; Labus, Markus; Huber, Franz; Stanzel, Melanie; Peukert, Wolfgang; Will, Stefan (37th International Symposium on Combustion, 2018)

Optical investigations on partially premixed diesel combustion for different operating parameters - Schmid, Marcus; Kaiser, Martin; Koch, Peter; Wensing, Michael; Leipertz, Alfred (SAE Technical Papers, 2008)
Combustion processes with partially or fully premixed cylinder load combined with self-ignition provide high combustion efficiency and low emissions of Nitrogen Oxides (NOx) and particulate matter at the same time. Since the number of diesel operated passenger cars is still rising, it would be interesting, if such a combustion concept can be realized in an ordinary DI-Diesel engine which is operated with conventional diesel fuel. In this study, the influence of nozzle geometry, Tintake, pTDC and injection timing on the functioning chain of combustion was analyzed in a transparent single-cylinder diesel engine equipped with a common rail injection system by means of optical measurement techniques. Simultaneously, different optical diagnostics (laser-based and non laser-based) were used to study the fuel distribution, ignition and combustion in the combustion chamber of the optically accessible diesel engine. The liquid fuel was visualized by Mie scattering at 532nm. The frequency tripled wavelength (355nm) of the same Nd:YAG-laser was used to obtain the spatial distribution of the fuel vapor and to visualize the quality of mixture formation with laser-induced fluorescence. The ignition process and the following combustion were detected in the UV spectral range. In order to distinguish between premixed and non-premixed combustion also the visible range of the combustion-light was detected The investigation shall demonstrate to what extent a premixed mixture can be reached and how the spatial distribution of the ignition locations as well as the combustion are affected. © 2008 SAE International.
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Optical Properties of Nanocrystal Interfaces in Compressed MgO Nanopowders - Mckenna, Keith P.; Koller, David; Sternig, Andreas; Siedl, Nicolas; Govind, Niranjan; Sushko, Peter V.; Diwald, Oliver (ACS nano, 2011)
The optical properties and charge trapping phenomena observed on oxide nanocrystal ensembles can be strongly influenced by the presence of nanocrystal interfaces. MgO powders represent a convenient system to study these effects due to the well-defined shape and controllable size distributions of MgO nanocrystals. The spectroscopic properties of nanocrystal interfaces are investigated by monitoring the dependence of absorption characteristics on the concentration of the interfaces in the nanopowders. The presence of interfaces is found to affect the absorption spectra of nanopowders more significantly than changing the size of the constituent nanocrystals and, thus, leading to the variation of the relative abundance of light-absorbing surface structures. We find a strong absorption band in the 4.0-5.5 eV energy range, which was previously attributed to surface features of individual nanocrystals, such as corners and edges. These findings are supported by complementary first-principles calculations. The possibility to directly address such interfaces by tuning the energy of excitation may provide new means for functionalization and chemical activation of nanostructures and can help improve performance and reliability for many nanopowder applications.
EAM Import::2019-03-08

Optimized Method of 3D Scaffold Seeding, Cell Cultivation, and Monitoring Cell Status for Bone Tissue Engineering - Krolinski, Adrian; Sommer, Kai Peter; Wiesner, Johanna; Friedrich, Oliver; Vielreicher, Martin (Cell Viability Assays (2nd Edt.), 2023)
The cultivation of cells in 3D systems is commonly regarded to be more physiological than in 2D as it comes much closer to the natural situation in tissues in many different aspects. However, 3D cell culture is much more complex. Cells within the pores of a printed 3D scaffold face a special situation concerning cell-material interaction and cell adhesion, cell proliferation, and supply of medium and oxygen into the core of the scaffolds. Biological assays (for cell proliferation, viability, and activity) have been validated primarily for 2D cell cultures and need to be adapted for 3D cultures. Likewise, in imaging, a number of points need to be taken into account in order to get a clear picture of the cells in 3D scaffolds, preferably with the method of multiphoton microscopy. Here, we describe a method for pretreatment and cell seeding of porous inorganic composite scaffolds (α-TCP/HA) for bone tissue engineering and for cultivation of the cell-scaffold constructs. The analytical methods described are the cell proliferation assay and the ALP activity assay. A step-by-step protocol is provided here that safely tackles typical difficulties that arise with this 3D cell-scaffold setting. In addition, MPM imaging of cells is described both with and without labeling. The combination of biochemical assays and imaging provides valuable insights into the possibilities of analysis with this 3D cell-scaffold system.
CRIS-Team Scopus Importer:2023-05-26
Keywords: 3D scaffolds; Cell adhesion; Cell proliferation; Cell seeding; Collagen-I formation; Multiphoton imaging; Osteogenic differentiation; Quantitative assays; Scaffold population; Second harmonic generation (SHG)

Optimized polybutylene terephthalate powders for selective laser beam melting - Schmidt, Jochen; Sachs, Marius; Fanselow, Stephanie; Zhao, Meng; Romeis, Stefan; Drummer, Dietmar; Wirth, Karl-Ernst; Peukert, Wolfgang (Chemical Engineering Science, 2016)
Additive manufacturing processes like selective laser beam melting of polymers (LBM) are established for production of prototypes and individualized parts. The transfer to serial production currently is hindered by the limited availability of polymer powders with good processability. Within this contribution the effect of powder properties, such as particle size, shape and flowability on the processability in LBM and their influence on device quality is exemplified for polybutylene terephthalate (PBT) materials. A process chain for the production of spherical polymer microparticles has been developed to obtain PBT powder materials. The process chain consists of three steps: first, polymer microparticles are produced by wet grinding. Second, the particle shape is engineered by rounding in a heated downer reactor to improve the flowability of the product. Third, a further improvement of flowability of the still cohesive spherical PBT particles is realized by dry coating with fumed silica. Moreover, properties of the PBT powders obtained along the process chain are thoroughly characterized with respect to structure and crystallinity by infrared spectroscopy, X-ray diffraction and differential scanning calorimetry. The effect of flowability, shape and bulk density on the powders’ processabilities in LBM is assessed by characterization of the quality of thin layers built in a LBM device. It is demonstrated that the device quality is strongly determined by particle properties: powders of good flowability and high bulk density are mandatory to obtain dense devices.
Keywords: Downer reactor; Dry particle coating; Flowability; Poly butylene terephthalate; Selective laser beam melting; Wet grinding

Optimized production of protein crystals: From 1D crystallization slot towards 2D supersaturation B22 diagram - Peukert, Wolfgang; Wanka, Johanna (Chemical Engineering & Technology, 2011)
The second osmotic virial coefficient, B, of protein solutions is a function of the protein interaction potentials and, thus, summarizes many solution parameters leading to crystallization or precipitation of proteins. B of hen egg-white lysozyme and bovine serum albumin was measured by static light scattering under the variation of pH, temperature, and crystallization agents. Comparing B values and precipitate morphology in a systematically analyzed range of solution conditions allows the construction of the so-called crystallization slot. The thermodynamic driving force for crystallization is supersaturation, which is set by the protein concentration and the solubility (related to B). Hence, besides the optimal B range, the protein concentration and, if solubilities are available, the supersaturation leads to a two-dimensional crystallization window where crystal formation is possible. This is shown in a generalized state diagram, where protein morphologies are solely determined as a function of protein concentration or supersaturation and interactions. The second osmotic virial coefficient, B, of protein solutions is a function of the protein interaction potentials. It therefore summarizes many solution parameters leading to crystallization or precipitation of proteins. Values of B were measured for different protein molecules under different solution conditions and were correlated to the results of crystallization experiments. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Crystallization; Lysozyme; Proteins

Optimizing the design of a multi-stage tangential roller threshing unit using CFD modeling and experimental studies - Hussain, Saddam; Lei, Xingpeng; Wu, Hongqi; Li, Hao; Song, Haiyan; Zheng, Decong; Jiawei, Wang; Li, Anbang; Farid, Muhammad Usman; Ghafoor, Abdul (Computers and Electronics in Agriculture, 2024)
Rising global population of the world is resulting higher demand for buckwheat being a high-quality food crop. In this study, the multi-stage shearing drum working mode was proposed to solve the problems of easy entanglement, blockage in threshing process due to inconsistency of ripening period, decrease grain breakage rate and loss rate and increase threshing efficiency. The designed threshing unit incorporates key components: frame, feeding wheel, main and secondary threshing drums, discharge unit, and concave plate. FEA and modal analysis were integrated to assure robust structural performance and stability of the threshing components within set limits, which were validated by indoor testing that confirmed the threshing drum's working frequency did not cause resonance. Single Factor Method identifies optimal conditions: 600 rpm, 7 mm, 1.2 kg/s for minimal grain breakage; 700 rpm, 9 mm, 1.2 kg/s for lowest grain loss. A three-factor, three-level orthogonal experiment validates these findings. In conclusion, optimal results are achieved with a drum speed of 600 rpm, feeding rate of 1.2 kg/s, and a threshing gap of 9 mm thus, minimizing both grain loss and breakage rates.
CRIS-Team Scopus Importer:2024-09-20
Keywords: Buckwheat breeding; buckwheat thresher; finite element analysis; model analysis; multi-stage threshing; RSM

Optimizing the Shelling Process of InP/ZnS Quantum Dots Using a Single-Source Shell Precursor: Implications for Lighting and Display Applications - Wang, Zhuang; Wegner, K. David; Stiegler, Lisa; Zhou, Xin; Rezvani, Azita; Odungat, Ahammed Suhail; Apeleo Zubiri, Benjamin; Wu, Mingjian; Spiecker, Erdmann; Walter, Johannes; Resch-Genger, Ute; Segets, Doris (ACS Applied Nano Materials, 2024)
InP/ZnS core/shell quantum dots (QDs), recognized as highly promising heavy-metal-free emitters, are increasingly being utilized in lighting and display applications. Their synthesis in a tubular flow reactor enables production in a highly efficient, scalable, and reproducible manner, particularly when combined with a single-source shell precursor, such as zinc diethyldithiocarbamate (Zn(S2CNEt2)2). However, the photoluminescence quantum yield (PLQY) of QDs synthesized with this route remains significantly lower compared with those synthesized in batch reactors involving multiple steps for the shell growth. Our study identifies the formation of absorbing, yet nonemissive ZnS nanoparticles during the ZnS shell formation process as a main contributing factor to this discrepancy. By varying the shelling conditions, especially the shelling reaction temperature and InP core concentration, we investigated the formation of pure ZnS nanoparticles and their impact on the optical properties, particularly PLQY, of the resultant InP/ZnS QDs through ultraviolet-visible (UV-vis) absorption, steady-state and time-resolved photoluminescence (PL) spectroscopy, scanning transmission electron microscopy (STEM), and analytical ultracentrifugation (AUC) measurements. Our results suggest that process conditions, such as lower shelling temperatures or reduced InP core concentrations (resulting in a lower external surface area), encourage homogeneous nucleation of ZnS. This reduces the availability of shell precursors necessary for effective passivation of the InP core surfaces, ultimately resulting in lower PLQYs. These findings explain the origin of persistently underperforming PLQY of InP/ZnS QDs synthesized from this synthesis route and suggest further optimization strategies to improve their emission for lighting and display applications.
CRIS-Team Scopus Importer:2024-10-25
Keywords: continuous flow synthesis; core/shell; InP/ZnS; quantum dots; single-source precursor

Optimum between purification and colloidal stability of ZnO nanoparticles - Marczak, Renata; Segets, Doris; Voigt, Michael; Peukert, Wolfgang (Advanced Powder Technology, 2010)
Crystalline ZnO quantum dots have been synthesized by hydrolysis of zinc acetate dihydrate with lithium hydroxide in ethanolic solution. By varying different parameters of the synthesis process, the size of the ZnO particles can be controlled. Detailed investigation of the ripening of the nanoparticles evidenced that despite of the well-known influence of ageing temperature and time, the presence of the reaction byproduct lithium acetate strongly affects the ripening behaviour. In particular, the particle size can be almost completely arrested by the removal of this byproduct via reversible flocculation of the ZnO nanoparticles using heptane as an antisolvent. A closer analysis of the repeated washing process shows an initial improvement of the colloidal stability of the ZnO nanoparticles during the first purification cycle as it mainly removes the lithium acetate from the suspension and not the stabilizing acetate groups directly bound to the particle surface. With further washing the remaining acetate ligands are unable to maintain the stabilization against agglomeration of the ZnO nanoparticles. Thus, there exists an optimum between purification progress and colloidal stability. These findings are also confirmed by calculations according to the DLVO theory, which show that there exists nearly no primary minimum of small ZnO nanoparticles below 5 nm in the presence of stabilizing acetate ions whereas the decrease in acetate ions bound to the particle surface leads to a more and more pronounced primary minimum. The present work is of particular significance for the preparation of purified colloidal ZnO nanoparticles for studies of their electrical and optical properties with respect to their wide range of potential applications.

Ordered Arrays of Gold Nanostructures from Interfacially Assembled Au@PNIPAM Hybrid Nanoparticles - Vogel, Nicolas; et al. (Langmuir, 2012)
In this Article, we report on the assembly of hybrid Au@PNIPAM core shell particles at the air/water interface, their transfer onto solid substrates, and the controlled combustion of the organic material to produce arrays of gold nanoparticles. A detailed investigation on the assembly behavior of such soft hybrid colloids at the air/water interface was performed by correlating the surface pressure area isotherms with SEM and AFM images from samples transferred at different surface pressures. The hybrid particles display a complex behavior at the interface, and we could distinguish three distinct phases with varying interparticle spacings at different compression. The transfer process presented enables the decoration of topologically structured substrates with gold nanoparticle arrays, and the order of the initial monolayers is retained in the arrays of inorganic gold nanoparticles. The change in monolayer morphology upon compression can therefore be used to tailor the interparticle distance between approximately 650 and 300 nm without exchanging the colloids. More sophisticated gold nanostructures can be patterned into symmetric arrays using a similar protocol, which we demonstrate for nanostars and nanorods.

Ordered nanopore arrays with large interpore distances via one-step anodization - Minguez Bacho, Ignacio; Scheler, Florian; Büttner, Pascal; Bley, Karina; Vogel, Nicolas; Bachmann, Julien (Nanoscale, 2018)
Preparation of pre-patterned alumina substrates using bottom-up techniques compatible with nanotechnology applications is still a challenge. We present a novel methodology to achieve superior order in 'anodic' alumina with large interpore distances by a convenient one-step anodization process. The use of transparent insulators renders such anodic layers applicable as templates for nanostructured photovoltaic or photoelectrochemical devices.

Organization of functionalized gold nanoparticles by controlled protein interactions - Kohut, Ananiy; Voronov, Andriy; Peukert, Wolfgang (Particle & Particle Systems Characterization, 2006)
Gold colloidal particles were synthesized and modified by molecular self‐assembly. In addition, the reaction of biotinylated colloids with a tetrameric protein, avidin, was studied by optical absorption spectroscopy and dynamic light scattering. The modification involves the chemisorption of octadecanethiol on the gold, with the further attachment of alkyl biotin and cross‐linking with avidin molecules. The specific interaction of avidin with biotin leads to the controlled cross‐linking of particles. The degree of flocculation was quantified using a semi‐empirical flocculation parameter and its dependence on the biotinylation system was studied. The measured data were in good agreement, showing the possibility of regulating the aggregation rate and size of the aggregates using the experimental time, degree of biotinylation, and avidin concentration. The morphology of the self‐assembled gold monolayers, from the aggregated particles, was imaged by high‐resolution scanning electron microscopy. The structure of the thin particulate film depends on the bulk aggregate size and aggregation rat
Keywords: Bio-recognition; Particle size distribution; Gold aggregates

Organometallic perovskites for optoelectronic applications (Conference Presentation) - Levchuk, Ievgen; Högl, Florian; Brandl, Marco; Osvet, Andres; Herre, Patrick; Hock, Rainer; Schweizer, Peter; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph; Peukert, Wolfgang (SPIE Nanoscience + Engineering, 2016, 2016)
Organometallic halide perovskites CH3NH3BX3 (B= Pb, Sn, Ge; X = I, Br, Cl) have become one of the most promising semiconductors for solar cell applications, reaching power conversion efficiencies beyond 20%. Improving our ability to harness the full potential of organometal halide perovskites requires the development of more reliable synthesis routines of well defined, reproducible and defect free reference systems allowing to study the fundamental photo-physical processes. In this study we present size and band gap engineering for organo-lead perovskites crystallites with various shapes and sizes ranging from the 5 nm regime all the way to 1 cm. Colloidal nano-crystals, micro-crystlline particles as well as single crystals are demonstrated with excellent purity and control in shape and size are demonstrated. The structural, optical and photo-physical properties of these reference materials are investigated and analyzed as function of their size and shape.
Keywords: particle; crystal; organometal; optoelectronics

Origin and use of SolidSim modules using as example the fluidized bed spray granulation, size reduction, and screening - Peukert, Wolfgang; Möhrl, Lothar; Drechsler, Jörg; Schmidt, Eberhard; Nitschke, Dirk; Toneva, Petya Ivanova (Chemie Ingenieur Technik, 2005)
Die Grundbausteine das SimulationssystemsSolidSim bilden sogenannte Units. Aus diesen Units werden im Rahmensystem des Program-mes flexibel komplexe Flieûbilder aufgebaut. So können in Simulationen die stationären Zustände unterschiedlichster Anlagenkonfigurationen unter Berücksichtigung variabler Prozessparameter untersucht werden.
Keywords: Simulation; solidsim; process; granulation; sieving; comminution

Origin of the Acoustic Bandgaps in Hypersonic Colloidal Phononics: The Role of the Elastic Impedance - Cang, Yu; Sainidou, Rebecca; Rembert, Pascal; Magnabosco, Giulia; Still, Tim; Vogel, Nicolas; Graczykowski, Bartlomiej; Fytas, George (Journal of Physical Chemistry B, 2022)
How phonons propagate in nanostructures determines the flow of elastic and thermal energy in dielectric materials. However, a reliable theoretical prediction of the phonon dispersion relation requires experimental verification both near to and far from the Brillouin zone of the nanostructure. We report on the experimental hypersonic phonon dispersion of hard (SiO2) and soft (polymer) fcc colloidal crystals infiltrated in liquid polydimethylsiloxane with different elastic impedance contrast using Brillouin light spectroscopy. We discuss the distinct differences with first-principles full elastodynamic calculations involving a multiple-scattering theory. Interparticle contacts strongly impact the long-wavelength speed of sound and the nature of the particle vibration resonance-induced hybridization hypersonic bandgap. The absence of the order-induced Bragg bandgap in SiO2 and its presence in soft opals cannot be fully accounted for by the theory, limiting its predictive power. Bridging the elasticity of the two colloidal crystals with suitable SiO2 core-shell (polymer) particles reveals an unprecedented crossover behavior in the dispersion relation. In view of many conversational parameters, the control tuning of phonon propagation in soft matter-based hypersonic phononics remains challenging.
CRIS-Team WoS Importer:2022-09-09

Packings of micron-sized spherical particles – Insights from bulk density determination, X-ray microtomography and discrete element simulations - Schmidt, Jochen; Parteli, Eric J.R.; Uhlmann, Norman; Wörlein, Norbert; Wirth, Karl-Ernst; Pöschel, Thorsten; Peukert, Wolfgang (Advanced Powder Technology, 2020)
The quantitative description of packing behaviour of particulate systems under consideration of realistic particle size distributions and material properties poses one challenging problem in powder technology, with impacts on a broad range of technological areas. Here we investigate the packing characteristics of micrometer to millimeter-sized, polydisperse spherical particle systems of glass, zirconia and copper by means of experimental measurements of the bulk density, X-ray microtomography (CT) and numerical simulations of the granular packings using a 3d discrete element method (DEM). The applied DEM method takes realistic material properties into account and considers the experimentally obtained particle size distributions as well as attractive inter-particle forces including adhesion (Johnson, Kendall, Roberts (JKR)) and non-bonded van der Waals (vdW) interactions. Good agreement of the packing densities predicted by DEM and observed in the experiments (bulk density determination & CT) is found. Moreover, we show that a simple mathematical expression for the packing fraction as a function of average particle size of the polydisperse powder system describes well our experimental and simulation results for all investigated materials, with only two fitting parameters. From the DEM simulations, the mean (first) coordination number in the respective polydisperse packing is extracted and discussed with respect to the experimentally obtained direct neighborhood detection from X-ray tomography and in context of previous works. The mean coordination number shows a rather broad variance due to the polydispersity of the samples considered. It also shows a remarkable dependency on the definition of particle contact. Therefore, caution is advised when evaluating coordination numbers with this quantity being highly dependent on the instrumental resolution.
CRIS-Team Scopus Importer:2020-04-24
Keywords: Bulk density; Discrete element method; Packings; X-ray microtomography

Painting by numbers: Nanoparticle-based colorants in the post-empirical age - Klupp Taylor, Robin; Seifrt, Frantiek; Zhuromskyy, Oleksandr; Peschel, Ulf; Leugering, Günter; Peukert, Wolfgang (Advanced Materials, 2011)
The visual appearance of the artificial world is largely governed by films or composites containing particles with at least one dimension smaller than a micron. Over the past century and a half, the optical properties of such materials have been scrutinized and a broad range of colorant products, based mostly on empirical microstructural improvements, developed. With the advent of advanced synthetic approaches capable of tailoring particle shape, size and composition on the nanoscale, the question of what is the optimum particle for a certain optical property can no longer be answered solely by experimentation. Instead, new and improved computational approaches are required to invert the structure-function relationship. This progress report reviews the development in our understanding of this relationship and indicates recent examples of how theoretical design is taking an ever increasingly important role in the search for enhanced or multifunctional colorants. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Keywords: colloids; core/shell nanoparticles; designed nanostructures; functional coatings; structure-property relationships

Parameter identification for continuous fluidized bed spray agglomeration - Golovin, Ievgen; Strenzke, Gerd; Duerr, Robert; Palis, Stefan; Bück, Andreas; Tsotsas, Evangelos; Kienle, Achim (Processes, 2018)
Agglomeration represents an important particle formation process used in many industries. One particularly attractive process setup is continuous fluidized bed spray agglomeration, which features good mixing as well as high heat and mass transfer on the one hand and constant product throughput with constant quality as well as high flow rates compared to batch mode on the other hand. Particle properties such as agglomerate size or porosity significantly affect overall product properties such as re-hydration behavior and dissolubility. These can be influenced by different operating parameters. In this manuscript, a population balance model for a continuous fluidized bed spray agglomeration is presented and adapted to experimental data. Focus is on the description of the dynamic behavior in continuous operation mode in a certain neighborhood around steady-state. Different kernel candidates are evaluated and it is shown that none of the kernels are able to match the first six minutes with time independent parameters. Afterwards, a good fit can be obtained, where the Brownian and the volume independent kernel models match best with the experimental data. Model fit is improved for identification on a shifted time domain neglecting the initial start-up phase. Here, model identifiability is shown and parameter confidence intervals are computed via parametric bootstra
Keywords: Population balance modeling; Identifiability; Parameter identification; Continuous fluidized bed spray agglomeration

Parameter study for the production of semi-crystalline polyetherimide particles via liquid-liquid phase separation and precipitation - Unger, Laura; Dechet, Maximilian; Fischer, S.; Schmidt, Jochen; Bück, Andreas (Procedia CIRP, 2022)
The production of micron-sized polymeric particles via liquid-liquid phase separation (LLPS) and precipitation was under investigation, as this study is a continuation of previous activities. Throughout the production process of LLPS, parameter variations were conducted in order to adjust the final product properties. These include the particle size distribution, the melting point, the specific melting enthalpy, the obtained particle shape and powder flowability properties. The herein adjusted parameters involve the polymer fraction in the solution, the rotation speed of the stirring unit and the cooling rate after dissolving the polymer-solvent mixture. The cooling rate and the polymer fraction defined both, the thermal and structural properties of the obtained semi-crystalline particles. A superior impact on the particle size distribution and morphology was obtained from the rotation speed of the stirring element. Thus, the resulting properties of precipitated microparticles can explicitly be controlled via the applied production parameters.
CRIS-Team Scopus Importer:2022-11-25
Keywords: High temperature thermoplast; Microparticles; Precipitation

Particle Adhesion Force Distributions on Rough Surfaces - Götzinger, Martin; Peukert, Wolfgang (Langmuir, 2004)
The effect of roughness on adhesion force distribution was studied in the gas phase. Spherical gold particles with diameters between 5 and 20 μm were generated in a flame process and glued onto atomic force microscope (AFM) cantilevers directly after. Nanostructured substrates with defined roughness were produced by a dip-coating process. The geometry of the adhering partners was determined by AFM imaging, and the adhesion force was measured with the AFM. Depending on the roughness of the particles and the substrates, three types of distribution functions can be identified; two of them can be explained with a simple model. The obtained adhesion force distributions not only agree with those experimentally recorded in previous studies of commercially important powders (e.g., alumina, toner, and gold on different substrates) but also agree with distributions reported in the literature.
UnivIS-Import:2015-03-09:Pub.2004.tech.ITC.mechve.adhesi_9

Particle attrition during pneumatic transport - Peukert, Wolfgang; Frye, Lars (Proceedings PARTEC 2004, 2004)
UnivIS-Import:2015-04-16:Pub.2004.tech.ITC.mechve.partic