A Novel L₃-Phase from a Ca-Salt of an Anionic Surfactant and a Cosurfactant

An L 3 -phase is observed for the first time in a ternary phase diagram of a Ca-salt of an α-sulfonated alkyl fatty acid methyl ester, the cosurfactant (2-ethylhexyl)monoglyceride and water. As for other ternary surfactant/cosurfactant systems, the L 3 -phase occurs with increasing cosurfactant/surfactant ratios after the L α -phase. Some properties of the newly observed L 3 -phases are the same as for other known L 3 -phases. It is a low viscosity, optically isotropic fluid with a low flow birefringence. The time constants τ of the electric birefringence results scale with τ ∼ Ø -3 . Its conductivity is very much higher than that of the neighboring L α -phase, but there are some marked differences from known L 3 -phases. This novel L 3 -phase is thermodynamically stable despite ionic structure of the surfactant. We found no two phase region between the L α and the L 3 -phase, and the L 3 -phase is stable over a wide cosurfactant/surfactant ratio between one and two. In SANS measurements it shows a broad correlation peak that occurs at about the same position as the sharper peak in the L α -phase. The structure of the L 3 -phase is demonstrated by FF-TEM micrographs.