Fachgebiet 01: Mechanische Verfahrenstechnik
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Item-typ:Veröffentlichung, Investigation of protein laden droplets in microfluidic applications(2025-10-14); ; ; This thesis explores the transport and breakup of emulsion droplets in micro-capillaries and capillary constrictions and examines the role of proteins as biological emulsifiers in these systems. The study involves modeling and simulation of liquid/liquid flow through capillary constrictions with varying dynamic contact angles, ranging from highly hydrophilic to highly hydrophobic conditions. Advanced advection schemes with geometric interface reconstruction are employed in the models for high interface advection accuracy in the simulations, alongside a sharp surface tension force model to mitigate spurious currents caused by numerical surface curvature treatment and the implementation of the surface tension as a body force. Stress singularities at the three-phase contact line are addressed using a Navier-slip boundary condition. The simulation results highlight the significant impact of wettability on the contact line propagation and interface deformation, defining distinct displacement regimes within the forced liquid/liquid displacement. These regimes are experimentally validated and evaluated. The research especially investigates the role of proteins as interface active components, particularly used in food technology, where they, due to their amphiphilic nature, stabilize liquid/liquid interfaces by lowering interfacial tension. Given the increasing use of sensitive animal- and plant-based proteins in the food industry, low-shear, low-stress homogenization methods like the premix-membrane emulsification have gained specific attention. However, challenges such as protein adsorption to membrane surfaces, leading to fouling and pore-blocking, persist. This study addresses how protein adsorption alters the system wettability and affects droplet breakup during emulsification. For this approach, generic configurations (straight micro capillaries with constriction) of membrane structures are utilized. Through molecular dynamic simulations the research quantifies the impact of protein adsorption on interfacial tension at liquid/liquid and liquid/solid interfaces. The Young-Dupr ́e equation is employed to convert interfacial energies into contact angles, which are validated through experimental studies. The calculated contact angles are used to simulate the droplet propagation through idealized pore structures. Results demonstrate that protein adsorption significantly impacts the wettability, thereby, affecting droplet propagation and interfacial stability. A specific hypothesis is tested regarding disulfide bonds in proteins like the whey protein β- lactoglobulin, which play a crucial role in maintaining secondary and tertiary structures. The study shows that the partial or complete removal of these bonds impacts protein structural rearrangement through intra- and intermolecular interactions, thereby altering their interfacial activity at oil/water interfaces. The numerical investigations contribute to a deeper mechanistic understanding of the structure-function relationship in emulsification processes, particularly concerning the interfacial adsorption behaviour of proteins.Dissertation22 38 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Anomalously low modulus of the interpenetrating-phase composite of Fe and Mg obtained by liquid metal dealloying(Elsevier Science, 2019-04-01); ; ; ; A bulk interpenetrating-phase composite consisting of immiscible Fe and Mg metals is fabricated by liquid metal dealloying. The composite exhibits an anomalously low value of the Young's modulus of 20 ± 3 GPa, when probed in compression. The Young's modulus values obtained from nanoindentation and ultrasonic measurements are, however, significantly higher than that in compression, but still remain lower than theoretical values obtained from the Hashin-Shtrikman bounds and a micromechanics model. Such a deviation is explained by the weak interfaces between Fe and Mg phases that promote phase boundary sliding upon mechanical loading, leading to a low effective modulus.Wissenschaftlicher ArtikelBand:16374 49 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Process Intensification of Metal Laser-based Powder Bed Fusion using Nanoparticle Additives(2026-04-16); ; 75 36 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Formulation and Rheological Characterization of Premix EmulsificationFormulation and Rheological Characterization of Premix EmulsificationWissenschaftlicher ArtikelBand:87Heft:8120 107 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Compaction-induced restructuring of aggregated nanoparticle films using the discrete element methodAggregated nanoparticle films find application in many fields such as gas sensing, solar cells and batteries. These films are characterized by size distributions of polydisperse primary particles and sintered particle aggregates that dictate both the response to external load and functional properties such as heat or charge transport. Mechanical compaction of the films strongly affects these properties in a way that can be quantified by the change of porosity and pore size distributions on the applied compacting pressure. The exact restructuring mechanisms of the aggregate architecture, however, remain unknown. Here, we apply Discrete Element Method (DEM) simulations to gain access to such restructuring mechanisms in TiO2 nanoparticle films synthesized by flame-spray pyrolysis. The ability of the sintered TiO2 aggregates to rearrange via mutual detachment, rolling or sliding events dictated by non-covalent, humidity-dependent interactions are known to be crucial to predict the correct response to compaction. In this work, the importance of elastic deformation of aggregates according to a novel sinter bridge model is elucidated. The best match between DEM simulations and experiments is obtained for bridges with a tensile and bending strengths substantially larger than bulk TiO2, consistently with a low probability of critical fracture initiation in nanometer-scale structures.Wissenschaftlicher ArtikelBand:34298 86 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Reducing cohesion of metal powders for additive manufacturing by nanoparticle dry-coating(Elsevier Science, 2021-02); ; ; ; Additive manufacturing processes, such as laser powder bed fusion, require steady powder processing but often exhibit poor flowability and low powder bed densities. Reducing the attractive Van-der-Waals force through nanoparticle coating can enhance initially poor flowability. We investigated the effect of dry-coating nanosized SiO2 on gas-atomized CoCrFeNi powders containing different amounts of particles < 20 μm with respect to nanoparticle concentration and mixing time. The dynamic angle of repose of a 0–90 μm powder reduced 50% and bulk powder density increased 30% with nanoparticle concentrations up to 0.153 wt.-%. The granular Bond-number was correlated with the powder flowability and porosity. The effect of mixing time was investigated with mixing two fractions 20–90 μm and 0–90 μm at a constant nominal nanoparticle surface area coverage of 128% for 2 to 1440 min. Short mixing times improved the flowability, while extensive mixing resulted in nanoparticle reagglomeration and deteriorated flow.Wissenschaftlicher ArtikelBand:37999 159