BRANCHED VISCOELASTIC SURFACTANT SOLUTIONS AND THEIR RESPONSE TO ELONGATIONAL FLOW

Several years ago, Munstedt and Laun reported on the influence of bran ching on the elongational flow properties of polymer chains (Munstedt and Laun, 1981). They concluded that, in addition to the molecular wei ght distribution, the degree of branching strongly affects the degree of strain thickening of the elongational viscosity in such a way that the maximum in this material function increases with branching. In a r ecent paper by Lin, a ternary system of dodecyldimethylamine oxide-sod ium laureth sulphate-sodium chloride surfactant solutions was investig ated by CryoTEM and rheology (Lin, 1996). He reported a linear relatio n between the added sodium chloride and the branching of the wormlike micelles. In this paper we present an investigation of these surfactan t solutions in elongational flow. Our results indicate that for branch ed micellar systems the presence of branching enhances the maximum of the elongational viscosity in the same manner as in the case of polyme r melts.