EXCESS GIBBS FREE-ENERGIES AND EXCESS VOLUMES OF MIXTURES CONTAINING NORMAL-ALKANES OR CYCLOHEXANE PLUS THIAALKANES OR DITHIAALKANES

Vapor-liquid equilibria, by head-space gas-chromatographic analysis of the equilibrated vapor phase directly withdrawn from the equilibratio n apparatus, and molar excess volumes, V(E), by means of a vibrating-t ube densimeter, of binary mixtures containing thiaalkanes or dithiaalk anes with n-alkanes or cyclohexane, were determined at 298.15 K. The e xcess molar Gibbs free energies, G(E), of the examined mixtures were o btained by a least-squares treatment of the equilibrium data. The G(E) and V(E) values indicate that the steric effect exerted by the alkyl groups adjacent to the S group causes a regular decrease of the G(E) ( or V(E)) with increasing the number of alkyl groups in the thiaalkane. A tentative approach, based on an additivity scheme of surface intera ctions combined with the scaled particle theory, is presented to estim ate the energies of solvation in terms of group contributions.