The physics of a model colloid polymer mixture

Abstract

The addition of non-adsorbing polymer to a colloidal suspension induces an interparticle ‘depletion’ attraction whose range and depth can be ‘tuned’ independently by altering the polymer’s molecular weight and concentration respectively. Over the past decade, one particularly simple experimental realization of such a mixture has been studied in considerable detail: nearly-hard-sphere particles of poly(methyl methacrylate) and random-coil polystyrene dispersed in simple hydrocarbon solvents (mainly cis -decalin). The simplicity of the system has enabled rather detailed comparison of experimental findings with theory and simulation. Here I review the current understanding of the equilibrium phase behaviour, structure, phase transition kinetics, and metastability of this model colloid–polymer mixture. These findings form a useful reference point for understanding more complex mixtures. Moreover, in some cases, insights gained from studying this model system have relevance beyond soft-condensed-matter physics, e.g. in understanding the liquid state, in controlling protein crystallization, and in elucidating the nature of glasses.