Two-phase shear band structures at uniform stress

Using NMR microscopy we measure the velocity distribution for a wormlike surfactant solution in the gap of a small angle cone-and-plate rheometer, This system, cetylpyridinium chloride/sodium salicylate 100 mM/60 mM, exhibits biphasic shear band structure when the applied shear rate exceeds the critical rate of strain beyond which a plateau is observed in the shear stress. The structure is characterized by two low/high shear interfaces and the region of high shear evolves by increasing width as the average gap shear is increased.