Understanding and manipulation of contact forces and corresponding bulk flow properties of chemically modified nanoparticles at controlled capillary bridge formation

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The aim of the project is the description and manipulation of contact forces of TiO2 nanoparticles under environmental conditions. Since, in the presence of humidity the inter-particle processes are dominated by capillary forces, a fundamental understanding of the water adsorption will be a key element in this study. However, the adsorbed water structure and thus the capillary bridge formation is influenced by various parameters like the particle morphology (e.g. particle size, roughness) as well as the surface chemistry (surface energy, adsorbate structure) and therefore needs to be analyzed on a molecular basis. The project will be performed cooperatively by the Particle Technology Group (PVT, Dep. Mechanical Engineering) and the chair for Technical and Macromolecular Chemistry (TMC, Dep. Chemistry).In order to derive a model capable of predicting particle behavior on a macroscopic scale, the processes involved have to be understood on a fundamental basis. Within the scope of this project we propose a multi scale approach ranging from experiments on an individual particle level (AFM and liquid bridge simulation) and investigations on small particle ensembles (combined QCM-D / FTIR) up to macroscopic shear test.In this context, the combined in-situ QCM-D / FTIR experiments will bridge the gap between experiments on an individual particle level and macroscopic shear test. Each of these experiments will give valuable insights on different aspects of the complex interplay between inter-particle forces and the surface chemistry under environmental control. Variation of surface chemistry by means of adsorption of functional organic molecules will facilitate the correlation of macroscopic particle behavior like water adsorption isothermes and bulk flow properties to nanoscopic effects like the presence and structure of adsorbate layers as well as the formation of capillary bridges while keeping the disperse properties constant.Since direct control of the particle properties is of outmost importance for such a fundamental study the synthesis of particles with controlled surface and morphology is necessary. Complementing the experimental results, a method for the numerical simulations of capillary bridges with arbitrary shape and the resulting forces on particles and without the need of approximations regarding the meniscus shape will be developed. Calculating forces of static liquid bridges and of capillary forces during separation of particles will allow the transfer to DEM simulations.