Dynamical behavior and structure of concentrated water-in-oil microemulsions in the sodium bis(2-ethylhexyl)sulfosuccinate systems

The dynamical structures are qualitatively estimated by the dynamic light scattering and the rheological measurements for sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water/n-hexane/sodium chloride systems in the concentrated region up to 50-60% of the volume fraction of the molecular aggregates. As the volume fraction increases, a very slow mode of relaxation stands out, which is interpreted not by the hindered motions of an individual spherical aggregate but by introducing ''clusters'' of the aggregates owing to attractive interactions between the aggregates. The effect of the attractive interaction is not negligible only when the volume fraction of the aggregates in the AOT microemulsion is rather high and the average distance between the aggregates is reduced, indicating that the attractive interaction is rather weak. Furthermore, the retardation effect on the decay of the concentration fluctuation due to the attractive interaction is stronger for higher salinity conditions.