Universal Scaling Form of the Equation of State of a Critical Pure Fluid.

Close to the liquid gas critical point, the linear treatment of the symmetrical onecomponent θ[sup 4] model to observe the fluid-restricted universality of the subclass of pure fluids is reversed. The comparison with the fitting results obtained from the recent applications of the crossover description to CO[sub 2], CH[sub 4], C[sub 2]H[sub 4], C[sub 2]H[sub 6], R134a, SF[sub 6], and H[sub 2]O confirms that the dimensionless characteristic two scale factors involved in this description are: (a) the critical compressibility factor and (b) the slope at the critical point of the reduced potential P/T T[sub c]/P[sub c] along the critical isochore. For the two-phase domain along the critical isochore, a precise formulation for the extension range of the fluid-restricted universality is given in terms of the reduced scaling size ... of the critical density fluctuations, expressed as a function of the dilated scaling field which measures the distance to the critical point below T[sub c]. The explicit definition of the microscopic length scale a[sub c] = ... which characterizes the short-range of the microscopic interac- tion, gives a correlative estimation of the crossover domain when ξ[sup -] a[sub c]. [ABSTRACT FROM AUTHOR]