Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants Part8. Pressure-jump study of the kinetics of micellar equilibria in aqueous solutions of alkanediyl-alpha,omega-bis(dimethyldodecylammonium bromide) surfactants

The pressure-jump relaxation technique has been used for a study of the kin etics of micellar equilibria in aqueous solutions of cationic surfactant di mers of the alkanediyl-alpha-omega -bis(dodecyldimethylammonium bromide) ty pe with alkanediyl = (CH2)(2), (CH2)(3), (CH2)(4), (CH2)(6), and (CH2)(8). Owing to experimental constraints the measurements were restricted to low c oncentrations, close to the surfactant critical micelle concentration. As f or conventional (monomeric) surfactants, two relaxation processes have been evidenced in favorable situations. The fast relaxation process is associat ed with the surfactant exchange between micelles and bulk phase. The slow r elaxation process is associated with the micelle formation-breakup. As for conventional surfactants the micelle formation-breakup proceeds via stepwis e entry-exit of one surfactant at a time into-from its micelles. At the dif ference of conventional surfactants, the rate constant for the entry of a s urfactant 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 cor responding conventional surfactants. (C) 2001 Elsevier Science B.V. All rig hts reserved.