Shear banding and the isotropic-to-nematic transition in wormlike micelles- art. no. 011501

Using deuterium NMR spectroscopy in a Couette cell, we observe shear-induce d nematic ordering in the concentrated wormlike-micelle system CTAB/D2O, an d our results are qualitatively consistent with birefringence studies, and in exact quantitative agreement with the degree of order measured in neutro n-diffraction measurements. The width of the nematic region depends on shea r rats, as well as on the temperature proximity to the equilibrium isotropi c-nematic transition. Comparison of the nematic order profiles with velocit y profiles obtained under identical conditions shows quite clearly that the nematic state is not identifiable with a highly sheared, tow viscosity lay er, and we conclude that the process of shearing induces a nematic start of high viscosity, possibly associated with mesoscale ordering. We present a simple model in which transition from the high shear branch to the viscous nematic branch is counterbalanced by subsequent relaxation of nematic order .