Gas-liquid critical temperatures of polydimethylsiloxane mixtures

Abstract

Gas-liquid critical temperatures of mixtures of polydimethylsiloxanes with between two and eight silicon atoms per molecule are reported. The possible effect of decomposition of the siloxane on the observed critical temperatures at temperatures above 600 K has been studied.

Critical temperatures have been compared with those predicted by the van der Waals one fluid model using the Lorentz-Berthelot rules. The agreement is good. The unlike interactional energy term needed to fit the data at equimole fraction has been calculated using the Lorentz combining rule for the unlike interactional volume term. Trends in the energy term with increasing size difference of the component molecules are discussed.