Critical properties of mixtures containing siloxanes

Abstract

The critical temperatures of mixtures of octamethylcyclotetrasiloxane with four hydrocarbons, hexafluorobenzene, perfluorocyclohexane and carbon tetrachloride and mixtures of hexamethyl-disiloxane with a hydrocarbon and hexafluorobenzene are reported. The results have been compared with the van der Waals model proposed by Rowlinson and coworkers. The unlike interactions derived are compared with those predicted by three combining rules and it is concluded that, for the hydrocarbon mixtures, the empirical van der Waals rule is superior to the geometric mean and Hudson and McCoubrey combining rules.

The van der Waals model with the geometric mean rule predicts that there should be a maximum in the (critical temperature, composition) curve for some of the systems studied here. No definite maximum has been observed in these systems.