Crossover criticality in ionic solutions

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. (C) 2001 American Institute of Physics.