Concentration fluctuations and surface adsorption in non-ideal binary mixtures. A light-scattering and surface tension study

Abstract

The concentration fluctuations and the surface tension of binary mixtures of non-electrolytes have been measured at 298.15 K, using light scattering and plate tensiometry. The results show that all the mixtures are highly non-ideal, and present an important tendency to homocoordination. All the mixtures studied present negative values of the excess surface tension. The combination of the results of both techniques allows one to calculate the excess surface adsorption Γ₁₂ of one of the components.

The experimental results have been compared with the predictions of several solution models that have been recently used for predicting Γ₁₂ from surface tension data. It has been found that, in spite of being used in many recent papers, the UNIFAC model leads to rather poor predictions. The experimental results have also been compared with the predictions of a lattice-fluid model, the agreement is not satisfactory.