Supramolecular equilibria in microemulsions

Several supramolecular structures in single phase microemulsions of oil and water are relatively ‘well known’ and include swollen water-in-oil micelles, swollen oil-in-water micelles, and irregular bicontinuous microstuctures with interpenetrating oil and water domains separated by a monolayer of surfactant. These supramolecular structures are as yet not sufficiently well understood to admit predictability with respect to predicting transformations from one such microstructure to another, and this omission is put before theorists as a challenge. Qualitative and quantitative experimental characterizations of such transformations are described. Breakpoints in conductivity, molecular self-diffuison coefficients, and viscosity serve as transition markers of such transformations. Order parameters derived from detailed self-diffusion analyses provide means for quantifying these transformations and illustrate the existence of competing equilibria among such supramolecular microstructures. The order parameter calculations reveal that the transition markers correspond to continuous transition points for microstructural change.