The formation of water-in-oil microemulsions using a concentrated saline aqueous phase

The formation of a water-in-oil (W/O) microemulsion with a water phase containing up to 30% w/w NaNO2 and diesel oil as the oil phase, with the cationic surfactant cetyltrimethylammonium bromide (CTAB) and an alcoholic cosurfactant has been examined. The cosurfactant chain length, alcohol isomerism, solution salinity, temperature, CTAB:alcohol ratio and the effect of combining various alcohols were studied. The best set of conditions for the formation of a microemulsion with a maximum salt concentration whilst utilising a minimal amount of surfactant have been determined. The use of short chain unbranched alcohols (C3-C5), especially 1-butanol, or a combination of short alcohols (1-butanol and 2-propanol), and a CTAB:alcohol ratio between 60:40 and 70:30, with 68:32 are seen to be of primary importance for microemulsion formation. In addition, the extent of the W/O region on the phase diagram is shown to be temperature dependent, with higher temperatures increasing the extent of the one phase region. (C) 1998 Elsevier Science B.V.