ORDERING IN CHARGED COLLOIDAL DISPERSIONS AND MACROIONIC SOLUTIONS - A DENSITY-FUNCTIONAL APPROXIMATION

We examine a density-functional approach for constructing the phase diagram of charged colloidal dispersions interacting through screened Coulombic (Yukawa) pontentials. The interaction potential used accounts for the finite size of the colloids (or, "macroions"). The theoretical calculations predict the three phases (body-centered cubic (bcc), face-centered cubic (fcc), and liquidlike) that have observed experimentally. The bcc structure, observed in the region of low electrolyte concentrations and relatively low volume fractions of the macroions, becomes unstable at higher electrolyte concentrations, and the theory predicts a bcc-to-fcc or liquid-to-fcc transition. The predictions are qualitatively consistent with the recently reported experimental results based on small-angle synchrotron X-ray scattering.