Phase behavioral changes in SDS association structures induced by cationic hydrotropes

Phase behavior of systems containing sodium dodecyl sulfate (SDS) as anionic surfactant and each of tetraethyl ammonium chloride (TEACl) and tetrabutyl ammonium bromide (TBAB) as cationic hydrotropes in the presence of water and heptane oil was studied. This combination was also used to formulate alcohol-free middle phase microemulsion at different salt concentrations. Anisotropy was detected by cross polarizer and polarized microscopy. Ultralow interfacial tension for microemulsion was calculated theoretically using Chun Huh equation. Micelles and inverse micelles were characterized by conductivity measurements. Liquid crystals did not appear in these short-chain hydrotropic systems. Microemulsion salinity scans for 1% SDS/TBAB (2:1 M ratio) at 25 °C, exhibited Winsor III type at an optimal salinity of 8.5% NaCl, whereas the optimal salinity was found to be 4% NaCl for 8% SDS/TBAB (1:1 M ratio).