Critical temperatures of mixtures of quasi-spherical molecules. Application of the “van der Waals” treatment to some organo-silicon compounds + hydrocarbon systems

Abstract

The critical temperatures of mixtures of the cycloalkanes (C5-C8) with tetraethylsilane (TES) and octamethylcyclotetrasiloxane (OMCTS) have been measured using the sealed capillary method. The results have been analyzed in terms of the “van der Waals” model proposed by Leland, Rowlinson and Sather. Unlike interaction energies have been derived using the Lorentz combining rule for the interaction distances. The interaction energies for the OMCTS systems are less than those predicted by the geometric mean rule but greater than those predicted by the Hudson and McCoubrey rule. The interaction energies for the TES systems are greater than those predicted by both rules except for the TES + cyclooctane system where the interaction energy is slightly less than predicted by the geometric mean rule. The unusual behaviour of the TES + cycloheptane system which has a maximum in the critical temperature against composition curve is discussed.