SELF-DIFFUSION OF SURFACTANTS, HYDROCARBONS, AND WATER IN AN L(1) PHASE AND A CUBIC PHASE - INFLUENCE OF SURFACTANT AND HYDROCARBON CHAIN LENGTHS

The pulsed field gradient NMR method has been used to determine self-d iffusion coefficients of surfactant molecules, solubilized hydrocarbon s, and D2O solvent in ternary N-alkyl-N,N-dimethylamine oxide/alkane/D 2O surfactant systems. In the micellar phase, diffusion is governed by hydrodynamic transport of the micelles, supplemented by an exchange o f solubilized hydrocarbon upon micellar collisions. This model is test ed by variations in both the surfactant chain length and in the size o f the hydrocarbon molecules. In the cubic (''ringing gel'') phase, the solvent still exhibits values of the diffusion coefficients that are typical for motion in a continuous water phase, with the microemulsion droplets acting as obstacles. Mobilities of the surfactant in the gel state are low and have been determined only for the surfactant with t he shortest chain length (C-12-DMAO). Exchange of hydrocarbon between micellar entities in the gel is found to occur by a hopping process; t he associated rate decreases with the surfactant chain length. The lat ter process is restricted to domains with sizes on the order of a few microns.