LINEAR RHEOLOGY OF ENTANGLED WORMLIKE MICELLES

We report on the statics and dynamics of long and flexible wormlike micelles made from cationic surfactants (cetylpyridinium ions) diluted in brine (0.5 M NaCl) with strongly binding counterions (salicylate ions). This survey was performed at ambient temperature by combining light scattering and rheology measurements. Varying the weight percent, phi, of surfactants from 0.1 % to 10 %, both dilute and semidilute regimes were studied. Above the crossover concentration phi* approximately 0.3 %, the viscoelastic properties are described by an almost ideal Maxwell relaxator. The overall rheological data are found to scale with the surfactant concentration with exponents close to those predicted from a recent stress relaxation model applied to living polymers. In addition, at high angular frequency, the complex elastic modulus results are interpreted in terms of crossover between the regimes of reversible scission and of breathing of the polymer-like chains. Contrary to earlier reports, the total average length of the micellar aggregates is found to increase with surfactant concentration as: L(phi)BAR approximately phi0.25-0.4.