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

The phase behavior for systems containing sodium bis(2-ethylhexyl sulfosuccinate) (AOT), with the cationic hydrotrope tetraethyl ammonium chloride (TEAC), in the presence of water and heptane were studied. Formulations of microemulsion for such systems and for systems containing the so called “extended surfactant” were carried out at different 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 using 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.