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

亚毫米级固体颗粒和液体的混合物在过程工程和工业生产的许多分支中发挥着关键作用。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，另一方面需要水。以粉末形式存在的药物在模制成药丸之前与液体粘合剂混合。在低液体饱和度时，湿颗粒集合体中颗粒之间的凝聚力可以用孤立的毛细管桥效应很好地描述。在润湿液体(相对于总样品体积)约2%以上的大范围液体饱和度中，人们发现大的液团簇，它们主导着颗粒组件的机械性能和组件内的液体传输。在本项目的框架内，我们的目标是开发一种在存在毛细管桥和液体团簇的情况下的内聚力的统一模型，该模型可以用于颗粒的接触动力学模拟。为此，我们希望修改现有的模型，以考虑毛细管桥的单个体积、桥和团簇之间的液体交换以及毛细管多体相互作用。这个项目的另一个目标是量化在颗粒在润湿液体存在的情况下接近、接触和脱离过程中观察到的不同的耗散过程。由此产生的粒子的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。该项目的长期目标是将颗粒动力学与液体传输模型相结合，即首先再现并现实地预测大时间和大长度尺度上颗粒的集体动力学。

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.