Simulation studies of colloidal phase behaviour: beyond effective one-component models

胶体悬浮液是一类流体，其中微观颗粒分散在液体溶剂中。实例出现在许多天然和合成的软物质系统中，包括胶束、蛋白质溶液、油-水乳液、液晶和血液。从技术上讲，胶体悬浮液在油漆，药物输送系统和润滑剂等各种应用中发挥作用。它们也普遍存在于洗涤剂和化妆品等消费品以及蛋黄酱等许多食品中。然而，在所有这些系统中，一个问题是关键，即悬浮液的稳定性，或更一般地说，其相行为。这项工作将采用计算机模拟来研究分散的胶体颗粒的性质，其中更小的纳米粒子已被添加。已显示此类添加剂显著改变分散体的物理性质，特别是胶体颗粒相分离或聚集成凝胶的倾向。这是因为添加剂改变了胶体颗粒之间的有效相互作用。然而，对于这是如何发生的以及它究竟如何取决于胶体-添加剂和添加剂-添加剂相互作用的完整理解，目前除了硬球系统之外还缺乏其他任何东西。我们将解决这个问题，在目前的工作中使用计算机模拟的简化模型，即高度尺寸不对称的二元流体混合物通过色散和库仑力相互作用。直到最近，这样的研究在技术上太难执行，但一个新的模拟方法开发的提议者现在提供了直接访问的问题，真实的实际利益。我们计划系统地阐明各种类型和浓度的添加剂对相行为的影响，并发现异国情调的自组装非均匀相发生的条件下，如调制结构或集群阶段。这种结构化的阶段潜在地提供了巨大的效用作为模板的纳米光刻，纳米电子学，光子晶体和蛋白质结晶。

Colloidal suspensions are a class of fluid in which microscopic particles are dispersed in a liquid solvent. Examples arise in a host of natural and synthetic soft matter systems including micelles, protein solutions, oil-water emulsions, liquid crystals and blood. Technologically, colloidal suspensions feature in applications as diverse as paints, drug delivery systems and lubricants. They are also prevalent in consumer items such as detergents and cosmetics as well as many foodstuffs like mayonnaise. However, in all such systems one issue is key, namely the stability of the suspension, or more generally its phase behaviour.This work will employ computer simulation to study the properties of dispersions of colloidal particles to which much smaller nanoparticles have been added. Such additives have been shown to dramatically change the physical properties of a dispersion, specifically the tendancy of the colloidal particles to phase separate or to aggregate into a gel. This happens because the additive modifies the effective interaction betwen colloid particles. However, a complete understanding of how this happens and exactly how it depends on the colloid-additive and additive-additive interactions is presently lacking for anything other than hard sphere systems. We shall address this issue in the present work using computer simulations of simplified models namely highly size-asymmetric binary fluid mixtures interacting via dispersion and coulomb forces. Until recently, such studies were technically too difficult to perform, but a new simulation method developed by the proposer now offers direct access to problems of real practical interest. We plan to systematically elucidate the effects of various types and concentrations of additive on phase behaviour and to discover the conditions under which exotic self-assembled inhomogeneous phases occurs, such as modulated structures or cluster phases. Such structured phases potentially offer great utility as templates for nanolithography, nanoelectronics, photonic crystals and protein crystallization.