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 potass ium bromide (KBr) has been measured as a function of surfactant and sa lt concentrations. The comparison between the experimental data and th e 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 paramete rs suggest that intermicellar branching occurs at high salt content. A n analysis of the data using the recent results of a Poisson renewal m odel 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 i nvestigated systems is in good agreement with the recent theoretical p redictions of Cates et al. as long as the stress relaxation of the sys tem does not depart too much from a single exponential.