A comprehensive approach to the surface tension of binary liquid mixtures

In order to describe quantitatively the nature and composition of the surfa ce layer in a binary liquid mixture, some equations are derived within the frame of the association solution model by Kretschmer and Wiebe. Bulk conce ntrations, properties of the pure compounds (surface tension sigma, molar v olume v and association constant K) and the constant for complexation K-AB are involved in such expressions. If molecules of both compounds are not ab le to form heterocomplexes only one adjustable parameter is necessary, whil e another one is included when K-AB not equal 0. The proposed set of equati ons acquires special significance when heteroassociation compels the surfac e tension of a solution to be higher (or lower) than that of both pure comp ounds. Different binary systems have been employed to test the obtained rel ationships, namely (THF + n-hexane, n-heptane, n-octane, n-nonane or n-deca ne), (ethanol or 1-propanol + n-hexane or n-heptane), and (THF + 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol or 1-decanol). Surface tension values for these mixtures were taken from the literature except those for the series (THF + 1-alkanol), which have been measured at the temperature 298.15 K by using a drop volume tensiometer. A simulated annealing method has been util ized in order to carry out the adjustments. Surface tension data are well d escribed by the proposed set of equations in all cases. (C) 2001 Elsevier S cience B.V. All rights reserved.