FLOW BIREFRINGENCE EXPERIMENTS SHOWING A SHEAR-BANDING STRUCTURE IN ACTAB SOLUTION

Experiments of flow birefringence have been performed on a concentrate d solution of CTAB submitted to shear in a Couette cell. Qualitative o bservations of the flow in the annular gap of the Couette device let u s clearly see that the flow is divided into two layers when the shear rate exceeds a critical value. This shear banding structure is shown o n a set of photographs. The extinction angle chi and the retardation p hi were measured as a function of the shear rate gamma for different t emperatures. The results are in agreement with the predictions of the shear banding theory.