Colloidal suspensions as model liquids and solids

Abstract

We here review some of our recent results on fluid-like and crystalline ordered colloidal suspensions. We have investigated the structure and the dynamical properties of strongly interacting charged latex particles. The interaction can be varied experimentally over a wide range and in a precisely controlled way. It gives rise to pronounced correlations between the particles, leading to ordered mesosocpic structures which bear striking similarities with atomic or molecular liquids and solids. These colloids therefore can be envisaged as model systems for condensed matter. Nevertheless, typical colloidal time and length scales as found in weakly interacting systems are retained throughout the whole phase diagram upon the formation of fluid, supercooled, and crystalline phases. We pay particular attention to demonstrate this in the structure-dependent self-diffusion dynamics. Due to the mesoscopic interparticle spacing the suspensions are easily probed by Bragg-scattering of visible light. This is used to determine the crystallization kinetics and the elastic properties of the resulting colloidal solids. The rigorous control of experimental parameters allows for quantitative tests of theoretical concepts. In the case of elasticity and diffusion, we detect strong systematic influences of the sample morphology. We also discuss how the determined equilibrium properties may contribute to the understanding of recent experiments in the presence of strong shearing fields.