31P NMR investigation of a ringing gel phase and adjacent phases

Abstract

The temperature-surfactant concentration phase diagram was examined for the dodecyltrimethylammonium dimethylphosphate/3-methyl-3-methoxybutanol/water ternary system. The phase diagram contained a highly elastic gel phase which is known as a “ringing gel phase”. The ringing gel phase and adjacent phases in the ternary system were investigated by polarized optical microscopy, freeze-fracture transmission electron microscopy, and 31P NMR. Globular textures were observed in an optically isotropic gel phase. Since the globules were larger than those found in an isotropic solution, the texture consists of domains of aggregated units in the cubic (I 1) phase. Structure units of domains are equivalent to microemulsions which are constructed by surfactant molecules and swollen by alcohol in the isotropic (L 1) phase. Characteristic polarized microscopic textures were visualized in two phases with higher surfactant concentrations. These phases were identified as being hexagonal (H 1) and lamellar (L α) liquid crystals which was confirmed by transmission electron microscopy. The 31P NMR signal of the ringing gel showed a sharp singlet the same as that of the L 1 phase, indicating the fully averaged anisotropic interaction of the aggregates. The characteristic NMR signals of the anisotropic hexagonal and lamellar liquid crystal phases displayed chemical shielding with an asymmetric lineshape.