Precise vapour-pressure measurements of the solubilization of benzene by aqueous sodium octylsulphate solutions

Abstract

Accurate vapour-pressure–solubility results have been obtained for aqueous solutions of sodium octylsulphate (SOS) and benzene at 15, 25, 35 and 45 °C. Thermodynamic constants are reported for reactions of benzene with SOS monomers and micelles; hydrophobic effects are important in stabilizing the aggregates formed between monomeric benzene and SOS species.

The observed non-linearity of degree of solubilization with benzene activity indicates that benzene molecules interact cooperatively within the micelles. A mass-action model, employing a form of the Poisson distribution equations modified to account for cooperativity, provides an excellent fit of all the solubilization data at each temperature. Activity coefficients are reported for benzene in the micellar species, as functions of temperature and micellar composition.