2H Nuclear magnetic relaxation of 1.1-2H hexadecyltrimethylammonium bromide in micellar solutions of nonaqueous polar solvents and their mixtures with water

• Published in: Langmuir 1990, Vol.6, p.1205
• Main Authors: Sjöberg, M, Henriksson, U, Wärnheim, T
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827

The 2H spin-lattice and spin-spin nuclear magnetic relaxtion rates were measured at different frequencies for α-deuterated hexadecyltrimethylammonium bromide in micellar solutions of nonaqueous and mixed solvent systems. Three nonaqueous polar solvents, viz., formamide, ethylene glycol, and N-methylformamide, and their mixtures with water were used. The two-step model for magnetic relaxation of surfactant aggregates was fitted to the frequency-dependent relaxation rates for the surfactant, yielding a local order parameter and correlation times for a fast local motion and for a slow aggregate motion. The measurements show that the surfactant aggregates in formamide, ethylene glycol, and their mixtures with water. No aggregation occurs in N-methylformamide at water contents lower than 50 wt%. Approximate aggregate radii, obtained from the slow correlation times, show that the aggregates formed in formamide and in ethylene glycol are smaller than in water. The local order parameter, obtained from the relaxation measurements as well as from the quadrupolar splittings in the hexagonal phases, increases with increasing water content both in the formamide and in the ethylene glycol systems.