Abstract
The formation process of Shear-bands in a wormlike micellar solution of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) in the large amplitude oscillatory shear (LAOS) is examined experimentally. A transient response of shear stress after applying a large amplitude sinusoidal strain is measured by rheometer with concentric cylinder. In order to observe the spatial distribution of the optical anisotropy in the flow field, a new visualization technique recently developed by the authors, which can evaluate distribution of both the birefringence and the orientation angle from a photograph taken by the crossed-Nicols method, was applied. The highly-birefringent layer was formed near the moving wall when the strain exceeds 2.3 in the LAOS flow. In the oscillation with the higher strain, the shear-bands are formed but the bands disappeared at when the strain turns to zero. Therefore, the formation and dissipation of the shear-bands are repeated in each cycle of the LAOS flow.
