Metal-ligand coordinated Ca(DS)2/C14DMAO/H2O system: Phase behavior and rheological property

Abstract

A metal-ligand coordinated surfactant system formed by calcium dodecylsulfate (Ca(DS) 2 )/tetradecyldimethylamine oxide (C 14 DMAO)/H 2 O was studied in terms of surface tension, conductivity, negative-staining TEM, phase behavior and rheological operation. In C 14 DMAO solution, when Ca(DS) 2 is added, metal-ligand complexes form between the Ca 2+ and N→O group of C 14 DMAO. Under this metal-ligand driving force, different phases can be obtained at different concentrations and different ratios of Ca(DS) 2 and C 14 DMAO. At the fixed C 14 DMAO concentration, L 1 -phase consisting of spherical micelles forms at first. With the addition of Ca(DS) 2 , the spherical micelles elongate to be wormlike micelles and then after an L 1 /L  -two phase region, the birefringent vesicle-phase (L v -phase) region is observed. When Ca(DS) 2 concentration continues to increase, a gel-phase region is found after the L v -phase region and then precipitates of undissolved Ca(DS) 2 appear. The transition between different phases is affected by temperature remarkably. The wormlike micellar solutions and vesicle solutions were checked by rheological measurements and showed apparent viscoelasticity at high surfactant concentrations. metal-ligand, phase behavior, L v phase, wormlike micellar phase, rheological property