Phase behavior of three-component ionic fluids

We study the phase behavior of solutions consisting of positive and negativ e ions of valence z to which a third ionic species of valence Z > z is adde d. Using a discretized Debye-Huckel theory, we analyze the phase behavior o f such systems for different values of the ratio (Z) over bar = Z/z. We fin d, for (Z) over bar > 1.934, a three-phase coexistence region and, for (Z) over bar > 2, a closed (reentrant) coexistence loop at high temperatures. W e characterize the behavior of these ternary ionic mixtures as function of charge asymmetry and temperature, and show the complete phase diagrams for the experimentally relevant cases of (Z) over bar = 2 and (Z) over bar = 3, corresponding to addition of divalent and trivalent ions to monovalent ion ic fluids, respectively.