Phase behavior of ionic solutions: Comparison of the primitive and explicit solvent models

Grand canonical Monte Carlo calculations are used to investigate the demixing transition in model ionic solutions where the solvent is explicitly included. Charged hard sphere ions in hard sphere, dipolar hard sphere and quadrupolar hard sphere solvents are considered and the results are compared with the primitive (continuum solvent) model. For all solvents considered, it is found that the demixing transition is in the same general region of the phase diagram and is roughly described by liquid-vapor equilibrium in the primitive model. However, details such as the precise location of the critical point and the width of the unstable region depend upon the exact nature of the solvent. (C) 1999 American Institute of Physics. [S0021-9606(99)50203-1].