NONLINEAR RHEOLOGY OF WORMLIKE MICELLES

Certain viscoelastic surfactant solutions show unusual nonlinear rheology: In steady shear, the shear stress saturates to a constant value while the first normal stress increases roughly linearly with shear rate over several decades. Here we explain this behavior in terms of the ''reptation-reaction'' model for the dynamics of reversibly breakable, polymerlike micelles. The constitutive equation for this model leads to a flow instability of shear-banding type. The limiting shear stress is predicted to be sigma* = 0.67G0 (with G0 the plateau modulus), in quantitative agreement with experiment.