Phase behaviour of deionized binary mixtures of charged colloidal spheres

TL;DR

This review discusses how binary mixtures of charged colloidal spheres exhibit diverse phase behaviors influenced by size and charge ratios, including stabilization of crystals and formation of various phase diagrams, with potential for future charge-tunable experiments.

Contribution

It provides a comprehensive overview of phase behaviors in charged colloidal mixtures, highlighting the effects of size and charge ratios on phase stability and structure.

Findings

Coulomb interactions stabilize crystal phases at low concentrations.

Various phase diagram types observed, similar to metal systems.

Formation of stoichiometric compounds at high concentrations.

Abstract

We review recent work on the phase behaviour of binary charged sphere mixtures as a function of particle concentration and composition. Both size ratios and charge ratios are varied over a wide range. By contrast to hard spheres the long ranged Coulomb interaction stabilizes the crystal phase at low particle concentrations and shifts the occurrence of amorphous solids to particle concentrations considerably larger than the freezing concentration. Depending on size- and charge ratios we observe upper azeotrope, spindle, lower azeotrope and eutectic types of phase diagrams, all known well from metal systems. Most solids are of body centred cubic structure. Occasionally stoichiometric compounds are formed at large particle concen-trations. For very low size ratios entropic effects dominate and induce a fluid-fluid phase separation. As for charged spheres also the charge ratio is decisive for the type of phase behaviour, future experiments with charge variable silica spheres are suggested.