Fluctuational parameters based on the Bhatia–Thornton theory for supercritical solutions: Application to a supercritical aqueous solution of n-pentane

Abstract

To study the structural fluctuation of supercritical solutions, we introduced three fluctuational parameters, a scattering factor, a density factor and a volume factor, which were based on the Bhatia–Thornton theory. In the present study, the density dependence of the structural inhomogeneity in a supercritical aqueous solution of n-pentane was discussed using the scattering factor and the density factor obtained from small-angle X-ray scattering and the fluid density measurements, respectively. Although both these factors have their maxima at the same density position in the case of neat supercritical fluids, a significant difference between the two factors is observed in the binary solution. The large difference occurs by the contribution of the concentration fluctuation in the system. Based on the difference between the factors, it is suggested that a phase separation of the system exists in the higher-fluid-density region.