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

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Abstract
The dependence on mole fraction of GE 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 GE 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 GE 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 d2GE m/dx2 2. Parameters derived from the dependence of GE 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.

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