Nature of Crossover between Ising-like and Mean-Field Critical Behavior in Fluids and Fluid Mixtures

Abstract

An analysis of experimental data for the susceptibility of fluids and of liquid mixtures in the critical region has been performed to elucidate the character of the nonasymptotic critical behavior. While fluids and fluid mixtures exhibit an ultimate crossover to Ising-like asymptotic behavior, the effective susceptibility exponent ${\ensuremath{\gamma}}_{\mathrm{eff}}$ approaches the universal value $\ensuremath{\gamma}\ensuremath{\simeq}1.24$ either from above (A) or from below (B). We conclude that simple fluids belong to type B, whereas more complex systems may belong to type A and show a sharper nonmonotonic crossover from mean-field to Ising-like behavior.