Clustering and self-assembly in colloidal systems

Abstract

A colloidal dispersion consists of small particles called colloids, typically tens of nanometers to a few micrometers in size, suspended in a solvent. Due to collisions with the much smaller particles in the solvent, colloids perform Brownian motion: randomly directed movements that cause the particles to diffuse through the system. In principle, this motion allow the system of particles to explore all configurations available to them, sampling all of phase space according to the Boltzmann distribution. Analogous to molecular and atomic systems, colloidal systems can form disordered gas and liquid phases, as well as more ordered phases such as crystals, liquid crystals, or finite-sized aggregates. Since the particles form these phases based purely on their interactions and the Brownian motion that results from thermal fluctuations in their solvent, the process of forming these ordered structures is called self-assembly. In this thesis, we study the self-assembly of a variety of colloidal systems. We attempt to determine what structures can be expected to form, investigate the order and stability of these phases, and examine the nucleation of self-assembled crystals. To do this, we make use of computers to simulate the behavior of colloidal particles in suspension. Depending on the system under consideration, we perform either Monte Carlo simulations or event-driven molecular dynamics. In particular, we study the self-assembly of particles of several shapes in external electric or magnetic fields, the phase behavior of hard colloidal cubes, and the phase diagrams of charged colloidal spheres with a constant surface potential. Furthermore, we investigate the nucleation of binary hard sphere mixtures, the self-assembly of colloidal particles in evaporating emulsion droplets, and the formation of colloidal micelles. Where possible, we compare our results with experimental findings in similar systems.