Crossover parametric equation of state for Ising-like systems - art. no. 026125

We present a parametric equation for the thermodynamic properties in the cr itical region of three-dimensional Ising-like systems which include fluids and fluid mixtures. The equation of state incorporates a crossover from sin gular Ising behavior asymptotically close to the critical point to classica l (mean-field) behavior further away from the critical point, characterized by two physical crossover parameters: a coupling constant related to the s trength and range of molecular interactions and a "cutoff" wave number for the critical fluctuations. In the asymptotic Ising limit, the crossover equ ation reproduces the most recent theoretical estimates for the universal ra tios of the leading and correction-to-scaling critical amplitudes. The equa tion has been tested by comparing it with recent experimental thermodynamic -property data for He-3 near its vapor-liquid critical point.