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.

• Received 30 July 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.045701