Changing micellar order, lever rule behavior and spatio-temporal dynamics in shear-banding at the onset of the stress plateau

Abstract

Rapid 2D NMR velocimetry and ²H spectroscopy was used to investigate the spatio-temporal flow dynamics of the wormlike micelle system cetyltrimethylammonium bromide and sodium nitrate in a cylindrical Couette device. The nonlinear rheological response of this system exhibits a stress plateau indicative of shear banding. At the onset of the stress plateau, we observed an evolution with increasing applied shear rate from a situation where the shear rate in the high shear band increases while the interface position remains stationary to the classic lever rule behavior. This transition corresponds to increasing micellar ordering and changing fluctuating dynamics.