Small-angle neutron scattering study of a pressure-induced phase transition in a ternary microemulsion composed of AOT, D2O, and n-decane

A small-angle neutron scattering experiment was carried out in order to investigate a pressure-induced phase transition in an AOT (dioctyl sulfosuccinate sodium salt)/water/n-decane system. The samples, 20.9%, 22.4%, and 23.0% of AOT, dissolved in an equal volume fraction of water and oil, are known to be a dense water-in-oil droplet structure at ambient temperature and pressure. With increasing pressure, a structural phase transition was observed. At higher pressure, the systems turned into two phases; a lamellar phase at the lower part of the cell and a bicontinuous phase at the upper part. A pressure dependence of the mean repeat distance for each structure was obtained. The disorder parameter both in the water-in-oil droplet structure at lower pressure and in the bicontinuous structure at higher pressure followed a unique function. [S1063-651X(99)04103-3].