The solubilization of propane by mixed micelles composed of sodium alkyl sulfates

Abstract

The solubility of propane has been determined at elevated pressures in aqueous solutions of sodium dodecyl sulfate (SDS) mixed with varying proportions of either sodium octyl sulfate (SOS) or sodium hexyl sulfate (SHS) at 25°C. The solubility of propane follows Henry's law in every instance. Above the CMC, the solubility of propane is found to increase linearly with total surfactant concentration in solutions containing a fixed ratio of SDS with either SOS or SHS indicating solubilization by mixed micelles of these species. The degree of solubilization varies in a continuous manner with surfactant composition. Critical micelle concentrations determined for these surfactant mixtures agree well with predictions based on the assumption that mixed micelles constitute a condensed pseudo phase which exhibits ideal solution behavior. The linear dependence between the extent of gas solubilization and the total surfactant concentration observed for each mixture above the CMC is interpreted according to this model to indicate that enhanced micellar gas solubility resulting from the enrichment in SDS content of the mixed micelles serves to compensate for a deficiency, relative to total surfactant concentration, of micellized surfactant ions.