Conformal-solution Theory of Polar Fluids: the Statistical Mechanical Basis of Shape Factors

The formalism of conformal-solution theory (CST) has been extended to pure and mixed polar fluids with consideration of dipolar, quadrupolar and induced dipolar forces. The total potential energy is reduced to a form similar to that for neutral molecules by statistical averaging over orientations. The temperature dependence,s of the conformal parameters f, and h,, are derived and it is found that the temperature variations are in opposite directions. These conformal parameters are related to Leland’s shape factors f&, and &,,, for which similar trends in temperature variations are observed. Following the theory of Byers-Brown for neutral molecular fluid mixtures, with the random-mixing approximation, an expression is derived for the excess Gibbs free energy of a binary polar mixture, using a generalized mixing-rule approximation.