Mean-Field to Ising Crossover in Ionic Fluids

Abstract

We present evidence for a classical to nonclassical crossover, in the osmotic compressibility (${\chi }_T$) of model ionic fluids, as $T_c$ is neared. ${\chi }_T$ was deduced from precision turbidity measurements. The phase separation in this class of ionic fluids is driven by the long-ranged Coulombic interactions. For a moderatively Coulombic case, we observed a complete crossover from near Ising asymptotic behavior to a fully established mean-field character. Our results indicate that the crossover region shifts away from $T_c$ as the Coulombic interactions are progressively lessened by increasing the dielectric constant ($\epsilon$) of the solvent.