Critical behavior of ionic-fluid models

It is argued that one should expect a fluid of symmetrically charged hard spheres (the restricted primitive model) to have an Ising-like critical point. It is further noted that the presence of a repulsive ${\mathit{r}}^{\mathrm{-}4}$ ion-ion interaction term (of the sort found in real ionic systems as a result of solvent-averaged ion-dipole-ion interaction) will prevent such a critical point from developing, although competing terms that suppress its effect may also be present in real electrolytes.