Excess of solubilization and curvature in nonionic microemulsions

We measure separately the amount of solute dissolved in a surfactant monolayer and the average curvature of the relevant sample to establish a link between these two quantities. The model system chosen involves the common hydrophobic pesticide lindane (gamma-C6H6Cl6) in a nonionic surfactant solution of the ethylene oxide type. Excess solubilization, defined as the solubilization in the surfactant film by comparison with bulk oil, is quantified by the interfacial composition lambda (molar ratio solute/surfactant) within the interfacial film. A linear relationship between the amount of solute adsorbed on the film and the induced variation in curvature of the surfactant film is deduced from the phase diagram, dosage, and small-angle scattering experiments in the case of micellar, Winsor I, and several Winsor III domains at equilibrium in the same ternary system, We discuss the linear relationship obtained with constraints set by molecular packing. (C) 1999 Academic Press.