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

胶体悬浮液是一种将微粒分散在液体溶剂中的流体。例子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，胶体悬浮液在涂料、药物输送系统和润滑剂等各种应用中发挥着重要作用。它们也普遍存在于洗涤剂和化妆品等消费品中，以及许多食品中，如蛋黄酱。然而，在所有这类体系中，有一个问题是关键，即悬浮液的稳定性，或者更广泛地说，它的相行为。这项工作将使用计算机模拟来研究添加了更小的纳米颗粒的胶体颗粒分散体的性质。这类添加剂已被证明可以极大地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，除了硬球体系外，目前还缺乏对这一现象如何发生以及它究竟如何依赖于胶体-添加剂和添加剂-添加剂相互作用的完整了解。我们将在目前的工作中使用简化模型的计算机模拟来解决这个问题，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还太难进行，但现在由提出者开发的一种新的模拟方法提供了直接进入真正实际感兴趣的问题的途径。我们计划系统地阐明不同类型和浓度的添加剂对相行为的影响，并发现外来自组装非均相发生的条件，例如调制结构或团簇相。这种结构相可能作为纳米光刻、纳米电子、光子晶体和蛋白质结晶的模板提供巨大的用途。

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.