Gas—liquid critical temperatures of binary mixtures containing a low molecular weight polydimethylsiloxane or hexaethyldisiloxane

Abstract

As part of an extensive study of the gas—liquid critical properties of binary mixtures the present paper reports critical temperature measurements on mixtures of polydimethylsiloxanes including tetrakis(trimethylsiloxy)silane, with a range of quasi-spherical molecules. This work considerably extends studies undertaken by one of us over a decade ago. The siloxanes offer the opportunity to study the critical properties of simple chain, cyclic or quasi-spherical molecules over a considerably greater range of molecular weight than is possible with hydrocarbons. Values of the interaction parameter, ξ, were obtained from the experimental results using the hard-sphere + attractive force one-fluid model. These interaction parameters, which in some measure, at least, reflect the relative strength of the interaction between pairs of unlike molecules, are compared with values from previous measurements on related systems. The interaction parameters obtained by fitting theory to experiment are also compared with values predicted using the relationship proposed recently by Sadus. The agreement, is, in general fairly good although not within the experimental uncertainty.