An inverse Kirkwood–Buff treatment of the thermodynamic properties of DMSO–water mixtures and cyanomethane–water binary liquid mixtures at 298.2 K

Abstract

The dependence on mole fraction of G^E_m for DMSO(2)–water(1) mixtures has been analysed using the Redlich–Kister equation. Derived parameters and other properties of this system have been used to calculate Kirkwood–Buff integral functions G₁₁, G₂₂ and G₁₂ which are related to spatial correlation functions for the liquid mixture. Trends in these parameters as a function of mole fraction composition point to the importance of the function G₁₂ consistent with strong intercomponent hydrogen bonding. The dependence of G^E_m on x₂ for water(1)—cyanomethane(2) mixtures is analysed using both Redlich–Kister and orthogonal polynomial functions. At 298.2 K and ambient pressure G^E_m > RT/2 for x₂≈ 0.4 which, for a quadratic mixture, signals partial miscibility. This complexity impinges on the analysis which requires the second differential d²G^E_m/dx²₂. Parameters derived from the dependence of G^E_m on x₂ using orthogonal polynomials are combined with other properties of this mixture to yield the Kirkwood–Buff integral functions. In contrast to DMSO–water mixtures, the dominant terms, G₁₁ and G₂₂, confirm the microheterogeneity of cyanomethane–water mixtures, where x₂≈ 0.3.