Complex Made from Tetrasodium N,N-Bis(carboxylatomethyl) Glutamate and Sodium Oleate that Forms a Highly Ordered Lamella in Gel Phase

Abstract

Abstract When we mixed two transparent aqueous solutions of tetrasodium N,N-bis(carboxylatomethyl) glutamate (GLDA) and sodium oleate (OleNa), a white gel phase was formed when the total solute concentrations were higher than about 2.8 wt %, indicating that complexation between GLDA and OleNa caused the gelation. The appearance of the gel was completely opaque, the gel displayed thixotropy, and the gel state changed to the sol state upon heating. Optical microscopy showed that the gel consisted of very long fibers with diameters ranging from nanometers to micrometers. Transmission electron microscopy showed that the long fibers were made from many bundled, straight fibrils with a width of 200–1000 nm. The fibril consisted of lamellae parallel to the axial direction of the fibril. X-ray scattering confirmed the lamellar structure with a spacing of 4.5 nm, and the spacing was independent of the concentration and the molar ratio of GLDA and OleNa. The area of the lamellar first peak reached a maximum at the molar ratio of GLDA:OleNa = 4:1, i.e., this ratio is the stoichiometry of the GLDA/OleNa complex. This stoichiometric number was confirmed by high-performance liquid chromatography.