A H-2 NMR relaxation study of a model microemulsion

The microemulsion phases of the Winsor system consisting of 47 wt% brine, 2 wt% sodium dodecylsulphate, 4 wt% butanol and 47 wt% toluene were investig ated by means of H-2 NMR relaxation on the surfactant which was specificall y deuterated in the alpha-position. The measurements were obtained at 20 de grees C for salinities varying from 3 to 10 g NaCl / 100 mi H2O. From a sim ple relaxation model the transverse relaxation rates were transformed into sizes of (spherical) droplets, which were compared with the droplet sizes o btained from the sample compositions in the Winsor I and II regions. For th e Winsor III region, the transverse relaxation rates could be rationalised in terms of a structural model based on bicontinuous cubic liquid crystalli ne phase. Moreover, by invoking previously obtained data, we show that the dependence on salinity of the water, oil and surfactant self-diffusion coef ficients can also be explained within the same framework.