Phase transitions in 2:1 and 3:1 hard-core model electrolytes.

Critical temperatures, T(c), densities, rho(c), and coexistence curves for 2:1 and 3:1 hard-core model electrolytes have been found by fine-discretization Monte Carlo simulation. The size ratio of + and - ions strongly affects T(c) and rho(c); the trends contradict most current theories. Large multivalent ions screened by small monovalent counterions exhibit normal gas-liquid transitions of direct relevance to phase separation in charge-stabilized colloids. Conversely, extrapolation suggests the absence of such transitions for sufficiently small multivalent ions with large monovalent counterions.