Van der Waals liquids, Flory theory and mixing functions for chlorobenzene with linear and branched alkanes

The basic assumption of the Flory theory of solution thermodynamics, van der Waals behaviour of the components, is contravened by chlorobenzene and other complex liquids. Their internal pressure decreases, instead of increasing, with decreasing volume. Using chlorobenzene with a series of normal alkanes and four highly branched isomers the following quantities have been measured at 25 °C and equimolar concentration: HE, VE, dVE/dT, dVE/dp, Δ(γVT), CEp, Δ(αγVT) and ΔCv. Against expectation, the Flory theory predicts the main trends of all these data. dVE/dT, Δ(γVT) and CEp for n-Cm systems show deviations from the theory which are readily explained by temperature-sensitive order in the long-chain pure n-Cm liquids. We conclude that the Flory theory remains useful, at least for chlorobenzene, in spite of the breakdown of its van der Waals assumption.