Crossover criticality in ionic solutions

Abstract

To examine the nature of criticality in ionic fluids we have analyzed experimental liquid–liquid coexistence and susceptibility data for various ionic solutions. We show that ionic fluids generally exhibit crossover or, at least, a tendency to crossover from Ising behavior asymptotically close to the critical point to mean-field behavior upon increasing distance from the critical point. This crossover is governed by two physical parameters: a rescaled coupling constant which reflects the strength and range of intermolecular interactions and a “cutoff” length. We conclude that the crossover critical behavior in ionic fluids is primarily governed by the cutoff length, which emerges as a new length scale that cannot be identified with the effective molecular-interaction range. An analogy between crossover critical phenomena in ionic fluids and in polymer solutions is discussed.