A 2H 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 investigated by means of ²H NMR relaxation on the surfactant which was specifically deuterated in the α-position. The measurements were obtained at 20°C for salinities varying from 3 to 10 g NaCl / 100 ml H₂O. From a simple relaxation model the transverse relaxation rates were transformed into sizes of (spherical) droplets, which were compared with the droplet sizes obtained from the sample compositions in the Winsor I and II regions. For the Winsor III region, the transverse relaxation rates could be rationalised in terms of a structural model based on a bicontinuous cubic liquid crystalline phase. Moreover, by invoking previously obtained data, we show that the dependence on salinity of the water, oil and surfactant self-diffusion coefficients can also be explained within the same framework.