Excess molar Gibbs energies of mixing of water and 1,1,1,3,3,3-hexafluoropropan-2-ol mixtures at 298.15 K. Comparison of thermodynamic properties and inverse Kirkwood–Buff integral functions for binary aqueous mixtures formed by ethanol, propan-2-ol, 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol

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Abstract
Vapour pressure data for water–1,1,1,3,3,3-hexafluoropropan-2-ol (HFPA) mixtures are analysed to yield excess molar Gibbs energies of mixing GE m at 298.15 K and ambient pressure. For this system GE m is positive in water-rich mixtures and negative in alcohol-rich mixtures. These data are used in conjunction with published volumetric data to yield dependences on liquid composition (1 ≡ water and 2 ≡ alcohol) of Kirkwood–Buff integral functions G11, G12 and G22. The trends in these integral functions as a function of mixture composition are compared with data for related binary aqueous mixtures including those formed by 2,2,2-trifluoroethanol. In water-rich mixtures both CH3 and CF3 are hydrophobic, enhancing neighbouring water–water interactions. In the fluoroalcohol-rich mixtures, intercomponent hydrogen-bonding interactions involve both OH-groups and C—F groups of the fluoroalcohol molecules.