Thermodynamics of ternary mixtures exhibiting tunnel phase behaviour Part 3.—Hexane–hexamethyldisiloxane–perfluorohexane

Abstract

The phase diagram for the ternary mixture hexane–hexamethyldisiloxane–perfluorohexane has been determined by visual observation of the liquid–liquid phase separation temperatures T _sep for the two partially miscible binary mixtures containing perfluorohexane and for three quasibinary temperature-composition slices of volume ratios of hexamethyldisiloxane:hexane of 1:3, 1:1 and 3:1. The upper critical solution temperatures T _UCS for the binary mixtures of hexane or hexamethyldisiloxane–perfluorohexane are separated by less than 1 K, being 295.76 K and 296.65 K, respectively. For the quasibinary slices, the maximum separation temperatures T _sep,max are lower than T _UCS for either binary mixture, for the central ternary slice T _sep,max = 294.64 K. The projections of the ternary liquid–liquid quasibinary slices map well on to the binary liquid–liquid coexistence curves. A simplified version of the statistical associating fluid theory (SAFT-HS) has been used to predict the phase equilibrium for this system and is in good qualitative agreement with the experimental results. In particular, the decrease in T _sep,max for the ternary mixtures is reproduced.