Is a birefringence band a shear band?

The discrepancy between the width of birefringence bands and shear rate ban ds in the system CTAB/water is addressed using a combination of NMR spectro scopy and NMR velocimetry. In correspondence with birefringence measurement s in the annular gap of a cylindrical Couette cell, H-2 NMR spectroscopy in dicates a separation of fluid into distinct nematic and isotropic phases. B y contrast the velocity profile exhibits an extremely narrow shear band, co nsistent with the predictions of the lever rule. Contrary to previous assum ptions, the experimental evidence points to a nematic phase with high visco sity.