Solute-solute and solute-solvent correlations in dilute near-critical ternary mixtures: mixed-solute and entrainer effects

Abstract

The asymptotic expressions for the solute-solute, cosolute-cosolute (cosolvent-cosolvent), solute-cosolute (solute-cosolvent), solute-solvent, and cosolute-solvent (cosolvent-solvent) total correlation function integrals of infinitely dilute ternary mixtures approaching the solvent's critical point are derived. All these integrals scale as the solvent's isothermal compressibility and diverge at the solvent's critical point. The sign of those diverging quantities depends on the behavior of the short-ranged infinite dilution solute-solvent and cosolute-solvent direct correlation function integrals. Some important implications of the peculiar microscopic behavior of these mixtures are discussed, such as (a) the irreconcilable incompatibility between the microstructure of dilute near-critical mixtures and the physical basis underlying the van der Waals one-fluid conformal solution mixing rules, (b) the prediction of mixed-solute and/or entrainer effects for ternary systems whose individual solute-solvent or solute-cosolvent binaries behave as either weakly attractive or repulsive mixtures, (c) the independence of the mixed-solute effect on the solute-solute, solute-cosolute, and cosolute-cosolute interactions, and (d) the independence of the entrainer effect on the solute-solute, solute-cosolvent, and cosolvent-cosolvent interactions. 41 refs.