Mechanical properties of dense granular assemblies in the presence of wetting liquids.

亚毫米大小的固体颗粒与液体的混合物在工艺工程和工业生产的许多分支中起着关键作用。例如，混凝土的生产，一方面需要颗粒材料水泥和沙子的均匀混合物，另一方面则需要水。以粉末形式存在的药物物质在模压成药丸之前与液体粘合剂混合。在低液体饱和度的湿颗粒组合中，颗粒之间的内聚可以用孤立的毛细管桥的作用来很好地描述。在超过约2%润湿液（相对于总样品体积）的大范围液体饱和度中，人们发现大的液体团簇，它们支配着颗粒组件的机械性能和组件内液体的运输。在本项目的框架内，我们的目标是开发一个统一的模型，用于毛细管桥和液体团簇存在时的凝聚力，可以实现颗粒的接触动力学模拟。为此，我们希望修正现有的模型，以考虑毛细管桥的个体体积，桥和簇之间的液体交换以及毛细管多体相互作用。本项目的另一个目标是量化在湿润液体存在下粒子接近、接触和分离过程中观察到的不同耗散过程。由此产生的粒子集体行为将在各种容器几何形状和不同的边界条件下进行研究。本项目的长期目标是将粒子动力学与液体输运模型结合起来，即首先再现，然后真实地预测大时间和长度尺度上粒子的集体动力学。

Mixtures of solid particles of sub-millimetric size and liquids play a pivotal role in many branches of process engineering and industrial production. The production of concrete, for instance, demands for a homogeneous mixture of the granular materials cement and sand on the one hand and water on the other hand. Pharmaceutical substances present in the form of powders are mixed with liquid binders before they are mold into pills. The cohesion between particles in a wet granular assembly at low liquid saturations can be well described by the effect of isolated capillary bridges. In the large range of liquid saturations above ca. 2% of the wetting liquid (with respect to the total sample volume) one finds large liquid clusters which dominate the mechanical properties of the particle assembly and the transport of liquid inside the assembly. In the framework of the present project we are aiming at the development of a unified model for cohesive forces in the presence of capillary bridges and liquid clusters which can be implemented to contact dynamics simulations of the particles. To this end we want to amend already existing models to account for the individual volume of capillary bridges, exchange of liquid between the bridges and clusters, and capillary many-body interaction. A further aim of this project is the quantification of different dissipative processes observed during approach, contact, and detachment of particles in the presence of a wetting liquid. The resulting collective behavior of the particles will be investigated in a variety of container geometries and for different boundary conditions. The long-term goal of this project is to combine the particle dynamics with models of liquid transport, that is, first of all to reproduce and then to realistically predict the collective dynamics of particles over large time and length scales.