Mean-Field to Ising Crossover in Ionic Fluids

We present evidence for a classical to nonclassical crossover, in the osmotic compressibility (${\ensuremath{\chi}}_{T}$) of model ionic fluids, as ${T}_{c}$ is neared. ${\ensuremath{\chi}}_{T}$ 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 ($\ensuremath{\epsilon}$) of the solvent.

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