2-SITE ADSOLUBILIZATION MODEL OF INCORPORATION OF ALCOHOLS INTO ADSORBED SURFACTANT AGGREGATES

The behavior of adsorbed surfactant aggregates, admicelles, was found to be very similar to that of micelles in the presence of alkanes. However, peculiar phenomena were observed in the incorporation of alcohols into admicelles: (i) very high ratios of alcohol to surfactant adsorption at lower coverages, (ii) remarkable increases of surfactant adsorption below the cmc, and (iii) a slight decrease of plateau adsorption. A two-site adsolubilization model is presented to interpret this complicated system. The hypothesis is that while the alkanes are adsolubilized only in a hydrocarbon core of the admicelle, there are two sites at which alcohols are adsolubilized, at the core and at the hydrophobic perimeter of the admicelle. The resulting model seems to be reasonable not only in explaining general trends in the alcohol and surfactant adsorption data but also in its estimates of aggregation numbers and the variation of aggregation numbers with alcohol and surfactant concentrations.