Stability of the liquid phase in colloidal electrolytes

The equilibrium phase diagram of a 1:1 symmetrical mixture composed of oppositely charged colloids is calculated using Monte Carlo simulations. We model the system by the DLVO effective interaction potential. The phase diagram is similar to that of its atomic analog (the ionic fluid), where a liquid-gas first order transition emerges in the low T-ρ regions being stable with respect to crystallization. As in the ionic fluids, we have found two different crystals: at high T, the fluid crystallizes in a FCC lattice, whereas at low T, the liquid coexists with a BCC crystal. The region of gas-liquid stability is observed to be narrower as the interaction range is diminished.