Thermodynamics of n-Alkane+Dimethylsiloxane Mixtures: Part 3.—Excess Volumes

Abstract

Excess volumes have been measured dilatometrically for binary mixtures of six n-alkancs (n- pentane, n-hexane, n-heptane, n-octane, n-dccane and n-tetradecanc) with four linear dimethylsiloxanes (dimer, trimer, tetramer and pentamer) at 303.2 K, and for four other mixtures. The sign and magnitude of the excess volumes depend intimately upon the chain lengths of the oligomers. The phenomenological corresponding states theory of Patterson is shown to reproduce qualitatively the experimental chain length dependence. Suggestions for the success of the model arc discussed briefly in terms of the properties of the pure components, and the disadvantages of two other approaches —the van der,Waals one-fluid model and the Prigogine cell theory—are identified. An application of Bransted’s principle of congruence to ternary mixtures is discussed.