Phase behavior and microstructure of water/trisiloxane E-12 polyoxyethylene surfactant/silicone oil systems

The ternary phase behavior of the trisiloxane E-12 polyoxyethylene surfacta nt with water and three low molecular weight silicone oils has been determi ned. The silicone oils were the tetra- and pentacyclosiloxanes, D-4 and D-5 , and the short linear tetrasiloxane, MD2M. Microstructures were investigat ed using small-angle X-ray scattering and polarized light microscopy. All t hree ternary systems exhibit similar phase behavior, forming surfactant-ric h and water-rich microemulsions, and liquid crystal phases. They follow the now familiar (2) under bar Phi (Winsor I) to three-phase (Winsor III) sequ ence with increasing temperature. Because of the large immiscibility gap be tween this very polar trisiloxane surfactant and the silicone oils, (2) ove r bar Phi (Winsor II) type behavior was not observed, even at elevated temp eratures (up to 140 degrees C). The cubic I-1 and I-3 phases were found in the ternary systems along with hexagonal H-1 and lamellar L-alpha liquid cr ystal phases, which persisted to substantially higher temperatures than the ir counterparts in the binary surfactant in water system.