Observation of Bulk Phase Separation and Coexistence in a Sheared Micellar Solution

We observe a shear-flow-induced phase transition in wormlike micelle solutions which depends on whether the applied stress or the applied shear rate is held constant. When the shear stress is held constant, the system macroscopically phase separates into two coexisting phases with a single stable interface between them. By contrast, when the shear rate is held constant, the system still undergoes a phase transition, but the steady states are homogeneous and no coexistence is observed. This leads to dramatically different rheological behavior and unusual long-lived metastable states.