Thermodynamic properties and structure of the water–ethanol silicone oil interface

Abstract

The interface between the water (1) – ethanol (2) system and silicone oil was studied over the whole composition range of the aqueous mixtures by means of adsorption and ellipticity measurements. The adsorbed layer was treated as a phase and, after derelativization of the relative surface excess, the adsorption isotherm (in term of molar fractions) as well as the activity coefficients of water and ethanol were calculated. From the above results and by analysing the ellipticity coefficient, we calculated the contribution to this latter due to the anisotropy of the adsorbed layer; the resulting "polynomial of anisotropy" was analyzed as a consequence of water and ethanol reorientations as the surface composition is changed.