Ionic fluid criticality solvent models

Most work has dealt with the RPM as a generic model for ionic criticality. MC data suggest that the replacement of the solvent s dielectric continuum by discrete solvent molecules does not change the principal topology of the phase diagram. This ensures that the simple RPM covers the major features of real ionic fluids, at least in cases where Coulombic interactions prevail. 

Mixtures of equisized charged spheres were also treated by the MSA. Such a system is then uniquely characterized by the ratio of the critical temperatures of the pure components. Harvey [235] found that a continuous critical curve from the dipolar solvent to the molten salt is maintained until the critical temperature of the ionic component exceeds that of the dipolar component by a factor of about 3.6. This ratio is much higher than theoretically predicted for nonionic model fluids. We recall that for NaCl the critical line is still continuous at a critical temperature ratio of about 5. Thus, the MSA of the charged-hard-sphere-dipolar-hard-sphere system captures, at least in part, some unusual features of real salt-water systems with regard to their critical curves. 

---