UNIVERSAL CROSSOVER-BEHAVIOR OF FLUIDS AND FLUID MIXTURES IN THE CRITICAL REGION

A new universal scaled equation of state for one-component fluids, binary mixtures, and ionic solutions, which represents the thermodynamic behavior of fluids in a wide range of temperatures and densities including the critical region, is proposed. Near the critical point this equation reduces to a theoretically based scaled equation including the leading nonasymptotic (Wegner) correction and a correction accounting for the asymmetry of fluids with respect to the critical isochore. Far away from the critical point the new equation goes over into the classical Landau expansion (van der Waals equation). The new equation is applied to represent experimental P-V-T data for H2O and CO2, as well as to represent C(v,x) data for dilute aqueous solutions of NaCl. A crossover from fluctuation to mean-field behavior is observed at increased concentrations of NaCl. A universal crossover function for the heat capacity C(v,x) of one-component fluids and binary mixtures is presented.