Shear banding fluctuations and nematic order in wormlike micelles

Using rapid NMR velocimetry we demonstrate the existence of shear band fluctuations in the Couette flow of the wormlike micelle system, 10% w/v cetylpyridinium chloride and sodium salicylate (molar ratio 2:1) in 0.5 M 2H2O NaCl brine. We show that the fluctuations may be either quasirandom or periodic, the fluctuation spectrum being similar to that observed in the stress. Despite the equilibrium fluid being far from an isotropic-nematic transition, deuterium NMR shows that the onset of shear banding is associated with a nematic micellar state whose order parameter depends on shear rate.