Tumbling Behaviour of Nematic Worm-like Micelles under Shear Flow

We report on the tumbling instability occurring in nematic solutions of worm-like micelles made of surfactant and subjected to low shearing fields ( ∼ 1 s -1 ). Results obtained by rheology and small-angle neutron scattering under shear are in good agreement with the mesoscopic domain theory developed recently for textured materials (such as liquid-crystalline polymers). When a stationary shearing is applied to these solutions, the tumbling results in oscillations in the shear stress responses, which in addition exhibit the scaling laws usually observed in liquid-crystalline materials. The neutron patterns on the other hand reveal that the average texture orientation increases after cessation of a shearing in the tumbling regime.