Direct Observation of Shear-Induced Structures in Wormlike Micellar Solutions by Freeze-Fracture Electron Microscopy

We report the first direct observation of shear-induced structures in low concentration wormlike micellar solutions. The structures consist of micron-sized patches which are much larger than individual equilibrium micelles and occupy 5%--10% of the fracture area. Such morphologies are consistent with recent reports of increased light scattering under shear flow. The structures have a stippled or spongelike texture and contain more surfactant than the background micellar solution. These patches form aggregates spanning hundreds of microns and are consistent with the shear thickening observed in these systems.