LINEAR AND NONLINEAR VISCOELASTICITY OF SEMIDILUTE SOLUTIONS OF WORMLIKE MICELLES AT HIGH-SALT CONTENT

The frequency-dependent shear modulus of semidilute aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) in the presence of potassium bromide (KBr) has been measured as a function of surfactant and salt concentrations. The comparison between the experimental data and the recent results of a computer simulation provides an estimate of tau(break), the time taken for a micelle of the mean length to break. The measured concentration dependences of rheological and kinetic parameters suggest that intermicellar branching occurs at high salt content. An analysis of the data using the recent results of a Poisson renewal model leads to the determination of a characteristic length, identified as the ratio of the total length over the sum of the end-caps density and of twice the connections density. The nonlinear behavior of the investigated systems is in good agreement with the recent theoretical predictions of Cates et al. as long as the stress relaxation of the system does not depart too much from a single exponential.