Criticality and tricriticality in ionic systems

The origin of the tricritical point (tcp) in ionic solutions and its dependence on the short-range effective free energies (SR) are studied within a Landau–Ginzburg–Wilson approach. The tcp is associated with a continuous transition to a charge-ordered phase, in which the charge density oscillates in space. SR interactions affect significantly the charge ordering and the position of the tcp depends sensitively on the strength, shape and state dependence of the SR potentials. The tcp can be located close to the coulombic critical point or close to the solvophobic critical point. For particular forms of the SR interactions either the tricritical or the critical point can be preempted by the occurrence of the other transition.