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环境条件下TiO 2纳米颗粒的接触力。由于，在湿度的存在下，颗粒间的过程主要是由毛细作用力，水吸附的基本理解将是本研究的一个关键因素。然而，吸附的水结构，从而毛细桥的形成受到各种参数的影响，如颗粒形态（如粒度，粗糙度）以及表面化学（表面能，吸附物结构），因此需要在分子的基础上进行分析。该项目将由粒子技术集团（PVT，Dep。机械工程）和主席的技术和高分子化学（TMC，部门。为了推导出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。在本项目的范围内，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）和小颗粒集合的研究（组合QCM-D / FTIR）宏观剪切测试。在这种情况下，组合在现场QCM-D / FTIR实验将弥合单个颗粒水平的实验和宏观剪切测试之间的差距。这些实验中的每一个都将对颗粒间力和环境控制下的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。通过功能性有机分子的吸附改变表面化学将促进宏观颗粒行为（如水吸附等温线和整体流动性质）与纳米级效应（如吸附质层的存在和结构以及毛细管桥的形成）的相关性，同时保持分散性质恒定。合成具有受控表面和形态的颗粒是必要的。作为对实验结果的补充，将开发一种数值模拟任意形状毛细桥及其对颗粒产生的力且无需对弯月面形状进行近似的方法。在颗粒分离过程中计算静态液桥力和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.