Alkanediyl-α,ω-bis(dimethylalkylammonium bromide) surfactants Part 8.: Pressure-jump study of the kinetics of micellar equilibria in aqueous solutions of alkanediyl-α,ω-bis(dimethyldodecylammonium bromide) surfactants

The pressure-jump relaxation technique has been used for a study of the kinetics of micellar equilibria in aqueous solutions of cationic surfactant dimers of the alkanediyl-alpha-omega -bis(dodecyldimethylammonium bromide) type with alkanediyl = (CH2)(2), (CH2)(3), (CH2)(4), (CH2)(6), and (CH2)(8). Owing to experimental constraints the measurements were restricted to low concentrations, close to the surfactant critical micelle concentration. As for conventional (monomeric) surfactants, two relaxation processes have been evidenced in favorable situations. The fast relaxation process is associated with the surfactant exchange between micelles and bulk phase. The slow relaxation process is associated with the micelle formation-breakup. As for conventional surfactants the micelle formation-breakup proceeds via stepwise entry-exit of one surfactant at a time into-from its micelles. At the difference of conventional surfactants, the rate constant for the entry of a surfactant dimer into its micelles is slower than for a diffusion-controlled process. Also the residence time of a surfactant dimer in its micelles and the lifetime of surfactant dimer micelles are much longer than for the corresponding conventional surfactants. (C) 2001 Elsevier Science B.V. All rights reserved.