Nanostructured Microemulsion Phase Behavior Using AOT or Extended Surfactant Combined with a Cationic Hydrotrope

Abstract

The phase behavior for systems containing sodium bis(2-ethylhexyl sulfosuccinate) (AOT), with the cationic hydro- trope tetraethyl ammonium chloride (TEAC), in the presence of water and heptane were studied. Formulations of mi- croemulsion for such systems and for systems containing the so called “extended surfactant”were carried out at differ- ent salt concentrations. Anisotropy was detected using cross polarizers and polarized microscopy. Ultralow interfacial tension for microemulsion was measured, first theoretically using the Chun-Huh equation, and then experimentally us- ing spinning drop experiments. The presence of short chain hydrotropes (TEAC) was found to destabilize the liquid crystalline region, observed in the AOT/water/heptane phase diagram. Ultralow interfacial tensions were observed for microemulsions formulated with surfactant concentrations as low as 0.5%, for both AOT and “extended surfactant” systems. The effect of temperature on the phase behavior of a microemulsion formed with AOT system was studied and found to behave in an opposite manner compared to the nonionic surfactant.