Influence of ion size and valence on classical ionic criticality

The symmetric Poisson–Boltzmann, modified Poisson–Boltzmann and the mean spherical approximation theories are used to investigate the coexistence region of the primitive model electrolyte for variations in ion size and valence. Calculations are made for 2:1, 3:1 valences with equal sizes and for 2:1, 1:2 valences with ion size ratio of 0.5. The theories indicate meanfield behaviour near the critical points but predict changes from the 1:1 primitive model in the coexistence region and at the critical points.