Solute‐induced effects on the structure and thermodynamics of infinitely dilute mixtures

Abstract

A general molecular‐based formalism developed rigorously establishes microscopic bases of the supercritical solubility enhancement in terms of well‐defined molecular correlation function integrals by unambiguously splitting the mixture's properties into short‐(finite) and long‐range (diverging) contributions. Consequently, the short‐range nature of the solute's and solvent's residual chemical potentials is proved and the change of the solvent's local environment around an infinitely dilute solute and its finite contribution to solute mechanical partial molar properties are interpreted in terms of the short‐range solute‐solvent and solvent‐solvent direct correlation function integrals. The solute‐induced effect on the system's microstructure and thermodynamics approaches zero as the mixture approaches ideality or the solute becomes an ideal gas particle. At the solvent's critical conditions, the solute‐induced effect on the solute's partial molar properties shows no compressibility‐driven singularity, though along the critical isotherm it can exhibit a finite extremum or a change of curvature near critical density, depending on the type and strength of solute‐solvent interactions. The utility of the proposed solvation formalism is illustrated using statistical mechanical integral equation calculations for three simple models of infinitely dilute near‐critical mixtures: pyrene‐CO 2, diterbutyl nitroxide‐ethane, and Ne‐Xe.