NATURE OF CROSSOVER BETWEEN ISING-LIKE AND MEAN-FIELD CRITICAL-BEHAVIOR IN FLUIDS AND FLUID MIXTURES

An analysis of experimental data for the susceptibility of fluids and of liquid mixtures in the critical region has been performed to elucid ate the character of the nonasymptotic critical behavior. While fluids and fluid mixtures exhibit an ultimate crossover to Ising-like asympt otic behavior, the effective susceptibility exponent gamma(eff) approa ches the universal value gamma similar or equal to 1.24 either from ab ove (A) or from below (B). We conclude that simple fluids belong to ty pe B, whereas more complex systems may belong to type A and show a sha rper nonmonotonic crossover from mean-field to Ising-like behavior.