VLE and LLE of perfluoroalkane + alkane mixtures

Vapour-liquid equilibria (VLE) of binary mixtures of n-perfluorohexane plus a n-alkane (C5-C8) and of n-hexane plus a n-perfluoroalkane (C5-C8) were determined using a head-space gas-chromatographic technique. Excess molar Gibbs energies, GE, for the systems investigated have been obtained by a least-square treatment of equilibrium data. Liquid-liquid equilibria (LLE) were determined by turbidimetry for n-perfluorohexane + alkane(C6-C8) mixtures and the observed T-x curves compared with those predicted by the temperature dependence of activity coefficients. All mixtures show strong positive deviations from ideality, which increase with the size of the second component. Solute-solvent and solute-solute interactions have been examined by calculating and discussing solvation Gibbs energies and Kirkwood-Buff integrals. Perfluoroalkanes proved to be inert molecules that interact weakly with themselves as well as with alkanes.