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

该项目的目的是描述和操纵二氧化钛纳米颗粒在环境条件下的接触力。由于在湿度存在的情况下，颗粒间的过程是由毛细力主导的，因此对水吸附的基本理解将是本研究的关键因素。然而，吸附水的结构和毛细桥的形成受到各种参数的影响，如颗粒形态（如粒径、粗糙度）和表面化学（表面能、吸附质结构），因此需要在分子基础上进行分析。该项目将由粒子技术小组（PVT，机械工程系）和技术与大分子化学主席（TMC，化学系）合作进行。为了推导出一个能够在宏观尺度上预测粒子行为的模型，必须在基本的基础上理解所涉及的过程。在这个项目的范围内，我们提出了一个多尺度的方法，从单个颗粒水平的实验（AFM和液桥模拟）和小颗粒整体的研究（结合QCM-D / FTIR）到宏观剪切试验。在此背景下，原位QCM-D / FTIR联合实验将弥合单个颗粒水平实验与宏观剪切试验之间的差距。这些实验中的每一个都将对环境控制下粒子间力和表面化学之间复杂相互作用的不同方面提供有价值的见解。通过功能有机分子的吸附而改变表面化学，可以在保持分散特性不变的同时，将宏观颗粒行为（如水吸附等温线、体积流动特性等）与纳米级吸附层的存在和结构、毛细桥的形成等联系起来。由于对颗粒性质的直接控制对于这种基础研究至关重要，因此合成具有可控表面和形貌的颗粒是必要的。在此基础上，提出了一种不需要半月板形状近似的任意形状毛细管桥的数值模拟方法。计算静液桥的力和颗粒分离过程中的毛细力将允许转移到DEM模拟。

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.