THERMODYNAMICS OF TERNARY MIXTURES EXHIBITING TUNNEL PHASE-BEHAVIOR .3. HEXANE-HEXAMETHYLDISILOXANE-PERFLUOROHEXANE

The phase diagram for the ternary mixture hexane-hexamethyldisiloxane- perfluorohexane has been determined by visual observation of the liqui d-liquid phase separation temperatures T-sep for the two partially mis cible binary mixtures containing perfluorohexane and for three quasibi nary temperature-composition slices of volume ratios of hexamethyldisi loxane:hexane of 1:3, 1:1 and 3:1. The upper critical solution tempera tures 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 separatio n temperatures T-sep,T-max are lower than T-UCS for either binary mixt ure,for the central ternary slice T-sep,T-max = 294.64 K. The projecti ons 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 predic t the phase equilibrium for this system and is in good qualitative agr eement with the experimental results. In particular, the decrease in T -sep,T-max for the ternary mixtures is reproduced.