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 TiO2 纳米颗粒的接触力。由于在存在湿度的情况下，颗粒间过程由毛细管力主导，因此对水吸附的基本了解将是本研究的关键要素。然而，吸附水结构以及毛细管桥的形成受到各种参数的影响，例如颗粒形态（例如颗粒尺寸、粗糙度）以及表面化学（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）和技术和高分子化学系主任（TMC，化学系）合作执行。为了导出能够在宏观尺度上预测粒子行为的模型，必须从根本上理解所涉及的过程。在该项目的范围内，我们提出了一种多尺度方法，范围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）到宏观剪切测试。在这种情况下，组合的原位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为环境控制下颗粒间力与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来改变表面化学将有助于将水吸附等温线和整体流动特性等宏观颗粒行为与吸附层的存在和结构以及毛细管桥的形成等纳米效应相关联，同时保持分散特性恒定。由于直接控制颗粒特性对于此类基础研究至关重要，因此有必要合成具有受控表面和形态的颗粒。作为对实验结果的补充，将开发一种对任意形状的毛细管桥及其对颗粒产生的力进行数值模拟的方法，而无需对弯液面形状进行近似。计算颗粒分离过程中的静态液桥力和毛细管力将允许转移到 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.