SHEAR BANDING STRUCTURE IN VISCOELASTIC MICELLAR SOLUTIONS

Theoretically, it has been shown that worm-like micellar solutions of surfactant can, for a shear rate (gamma) over dot greater than a criti cal value (gamma)(c) over dot, undergo a transition giving a plateau e volution (sigma = sigma(c)) Of the shear stress a against shear rate ( gamma) over dot. We report here on a experimental study of the linear and nonlinear rheological behaviour of aqueous CTAB solutions with NaN O3 as added salt. With this system, it is possible to observe the evol ution of the fundamental characteristics of the flow curve, i.e., the shear rate (gamma)(1c) over dot at which a shear banding structure app ears and the second critical shear rate (gamma)(2c) over dot character izing the end of the shear stress plateau followed by a new increased shear stress. For the first time, experimentally, we obtained evidence for the existence and the evolution of (gamma)(2c) over dot against C TAB and salt concentrations and temperature variations. Experimental r esults are compared to theoretical predictions correlating sigma(c), ( gamma)(1c) over dot and G(0) (the shear modulus) for Maxwellian micell ar solutions.