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 micelle s, swollen oil-in-water micelles, and irregular bicontinuous microstructure s with interpenetrating oil and water domains separated by a monolayer of s urfactant. These supramolecular structures are as yet not sufficiently well understood to admit predictability with respect to predicting transformati ons from one such microstructure to another, and this omission is put befor e theorists as a challenge. Qualitative and quantitative experimental chara cterizations of such transformations are described. Breakpoints in conducti vity, molecular self-diffuison coefficients, and viscosity serve as transit ion markers of such transformations. Order parameters derived from detailed self-diffusion analyses provide means for quantifying these transformation s and illustrate the existence of competing equilibria among such supramole cular microstructures. The order parameter calculations reveal that the tra nsition markers correspond to continuous transition points for microstructu ral change. (C) 2000 Elsevier Science B.V. All rights reserved.