We report evidence for two distinct strain-induced orientation transitions in a lyotropic bcc cubic crystal submitted to increasing shear rates. The crystal is built up from copolymer spherical micelles in a selective solvent. The distribution of orientations is characterized by x-ray diffraction: in the two oriented states, the dense 〈111〉 rows align along the flow, but they differ from each other in the orientations of the dense layers with respect to the shear plane. These orientation transitions have clear rheological signatures in the form of two stress plateaus each associated with the coexistence of two states of orientation. We compare this behavior with the well documented shear-induced orientation transition in wormlike micelles.

• Received 30 August 1999

DOI:https://doi.org/10.1103/PhysRevE.61.6759