STUDY OF INTERMOLECULAR INTERACTIONS AND MICROSTRUCTURE OF SUPERCRITICAL MIXTURES WATER-HEPTANE AND WATER+N-HEXANE BASED ON PVTX MEASUREMENTS(N)

The partial molar volumes of n-heptane and n-hexane in super- and near ly critical wafer are determined based on the PVTx measurements of the binary mixtures water+n-heptane and water+n-hexane near the critical point (CP) of the pure solvent (wafer). The partial molar volumes of n -heptane and n-hexane (V) over bar(2)(infinity) show nonclassical (sca ling) behavior ((V) over bar(2)(infinity) approximate to x(-gamma/beta delta)) as the system asymptotically approaches (x-->0) the CP of pur e water along the critical isobar-isotherm (T-c, P-c). The microstruct ure of the supercritical mixture is studied based on our experimental (PVTx, (V) over bar(2)(infinity)) data and Kirkwood-Buff's fluctuation theory of dilute solutions, the dependence of the cluster size (N-1(i nfinity)) on thermodynamic conditions (T, P) is established. With mino r variations of temperature and pressure near the CP of pure water, th e cluster size changes anomalously abruptly. The parameters of the equ ation of state of the SPHCT model are determined based on the PVTx mea surements, and direct solvent-solute correlation integrals C-12(infini ty) (of water+n-heptane and water+n-hexane) are calculated The Krichev skii parameter (partial derivative P/partial derivative x)(VT)(C), ade quately defining the behavior and structure of an infinitely dilute mi xture near the CP of the pure solvent, is calculated. The effects of i nteractions between the solvent and solute molecules on the structure of a supercritical fluid are examined.