Unusual interfacial behaviour of mixtures of 2,2,2-Trifluoroethanol with hydrogenated alcohols

New experimental data is reported for the surface tension of mixtures of 2,2,2-trifluoroethanol with three hydrogenated alcohols, namely ethanol, 1-propanol and 1-butanol, at 293.2 K along the full composition range. The phase equilibria, bulk properties of the mixtures and interfacial properties were modeled with soft-SAFT combined with the density gradient theory. Excellent agreement was found between predictions from the theory and the experimental results, the model allowing interpreting the interfacial behaviour of the mixtures, providing a microscopic explanation of the unusual interfacial behavior of these particular mixtures. Negative aneotropy (minima in the surface tension vs composition curve) is observed for the three mixtures. Negative aneotropy is a rare and poorly understood phenomenon usually associated to weak intermolecular interactions between the components of the mixture, which is not the case in these systems as the components interact strongly through hydrogen bonding. To the best of our knowledge, this is the first reported example of this type of negative aneotropy.