Mixtures with “w-Shape” CEp curves. A light scattering study

The Rayleigh ratio has been obtained for the following mixtures of non-electrolytes that show “w-shape” CEp vs. x curves: Nitrobenzene + n-Heptane, 1,4-Dichlorobutane + n-Heptane and Acetone + n-Dodecane. From them, the concentration-concentration correlation function Scc(0) has been calculated, as well as the excess Gibbs energy. It has been found that a clear tendency to homocoordination is present in all the mixtures studied. There is a rough correspondence between the concentration at which the maximum of the Scc(0) curves occur and those at which the negative curvature regions exist in the CEp curves. Also the larger the value of max. Scc(0) the more intense the “w-shape” effect. Despite size differences between the components and specific interactions which complicate the connection between Scc(0) and CEp, an analysis in terms of simple mean field models supports the view that the systems which show “w-shape” CEp curves still feel the effects of the more or less distant UCST. Hence Scc(0) is proposed as an indicator of the “w-shape” CEp.

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