A. Introduction

By surface tension of liquid mixtures it is meant here the property of the liquid mixture-gas interface. This is to avoid confusion with the interfacial tension property. The latter is usually reserved for liquid-liquid interfaces and, like surface tension, it arises because of different attractive intermolecular forces acting on the molecules of the two neighbouring liquid phases. Interfacial tension controls the miscibility of liquids. There is no interfacial tension at play for miscible liquids.

B. Liquid mixture surface tension

(a) Correlation of Macleod-Sudgen

The Macleod-Sudgen correlation Macleod (1923) (Equation 502.1) for pure liquids has been extended to liquid mixtures in the following form