Surfactant-specific electrode measurements of mesophases. Electrode and X-ray measurements of hexadecyltrimethylammonium bromide/hexadecanol gel (L-beta) dispersions show large, nonequilibrium dissolution effects

A commercially available surfactant-specific electrode has been employed to investigate the dilution behavior of hexadecyltrimethylammonium bromide/he xadecanol gel phase (L-beta) dispersions. Initial measurements on known sur factants demonstrated that the electrode gave reliable data. The structure of the gel phase and the extent to which it swells in water were establishe d by optical microscopy and X-ray diffraction. Surprisingly large nonequili brium concentrations of monomeric hexadecyltrimethylammonium bromide occur in gel phase dispersions immediately after dilution, which can reach the cr itical micelle concentration of the pure surfactant. Much lower levels occu r after some time (hours to days). These time-dependent changes are likely to be important in the practical applications of gel phase surfactants as e mulsion stabilizers or in conditioning products.