Interfaces and dynamics in complex fluids: non-additive mixtures

胶体分散体是由介观颗粒组成的复杂流体，大小在1纳米到1微米之间，分散在液体中。有各种各样的不同类型的颗粒，具有不同的形状、大小、电荷、表面和介电性质，以及相当大范围的不同类型的溶剂，包括水溶剂和非水溶剂，其中还包括添加剂，如盐或耗尽剂。日常生活中的胶体分散物包括牛奶、血液和油漆。除了具有许多重要的工业应用外，表征良好的合成胶体分散体是研究凝聚态物质中各种基本体、界面和动力学现象的重要模型体系。在这里，我们考虑两种不同类型的粒子的胶体分散的理论模型。这两个物种都被建模为硬球体；然而，不同种类的球对之间的交叉相互作用与人们从它们的几何形状推断的不同，即斥力发生在小于或大于单个直径的算术平均值的距离上。这种非加性硬球模型具有有趣的性质，从液-液相分离的发生到高密度的聚类现象。在真胶体分散体中，由于粒子上存在电荷或磁偶极子而发生非可加性。我们将利用先前开发的密度泛函理论以及计算机模拟来研究非加性硬球模型的各种相关界面和动力学现象。我们的目标是深入了解控制该模型的长度尺度的竞争如何影响自由液-液界面的特性，壁上和毛细血管中的吸附行为，以及体积和界面中的动态相关性，以及这些界面如何响应驱动系统失去平衡的外部场，例如在沉积动力学和分散暴露于剪切流中。

Colloidal dispersions are complex fluids of mesoscopicparticles with sizes between 1nm and 1micron that are dispersed in aliquid. There is a large variety of different types of particles withvarying shape, size, charge, surface and dielectric properties, aswell as a considerable range of different types of solvents, bothaqueous and non-aqueous, which also include additives such as salt ordepletion agents. Everyday examples of colloidal dispersions includemilk, blood, and paint. Besides possessing many important industrialapplications, well-characterized synthetic colloidal dispersions serveas important model systems to investigate a wide variety offundamental bulk, interfacial and dynamical phenomena in CondensedMatter.Here we consider a theoretical model for colloidal dispersions withtwo different types of particles. Both species are modelled as hardspheres; the cross interaction between pairs of spheres of unlikespecies is however different from what one would infer from theirgeometric shapes, i.e. the repulsion occurs at a distance that issmaller or larger than the arithmetic mean of the individualdiameters. This non-additive hard sphere model has interestingproperties ranging from the occurrence of liquid-liquid phaseseparation to clustering phenomena at high densities. In realcolloidal dispersions non-additivity occurs due to the presence ofelectrical charges or magnetic dipoles on the particles.We will investigate a wide variety of relevant interfacial anddynamical phenomena of the non-additive hard sphere model using bothour previously developed density functional theory for this model aswell as computer simulations. Our aim is to gain insight into how thecompetition of the length scales that govern this model affects theproperties of free liquid-liquid interfaces, of adsorption behaviourat walls and in capillaries, and of dynamical correlations in bulk andat interfaces, and how such interfaces respond to external fields thatdrive the system out-of-equilibrium, as is relevant e.g. in thedynamics of sedimentation and for dispersions exposed to shear flow.