Linear viscoelasticity of wormlike micellar solutions found in the vicinity of a vesicle-micelle transition

Linear viscoelastic behavior of micellar solutions of cetyltrimethylammonium hydroxynaphthalene carboxylate is studied at temperatures above the vesicle-micelle transition under salt-free conditions and also in the presence of salt (sodium bromide and potassium acetate). The salt-free solutions, beyond a crossover volume fraction phi*, obey the micellar growth model of Mackintosh et al. The low values of phi* indicate that the effective charge on the micelles is very low. The decrease of the terminal relaxation time upon increasing surfactant concentration for volume fractions larger than similar to 6 phi* is attributed to the formation of intermicellar connections, favored by the diminution of the electrostatic contributions. A similar effect is found by the addition elf a salt that does not bind with the surfactant. The phase diagrams shown in this study suggest that the branched micelles constitute the inter mediate structures between linear micelles and bilayers.