Investigation of shear-banding structure in wormlike micellar solution by point-wise flow-induced birefringence measurements

摘要

Shear banding occurs in many wormlike surfactant solutions subject to strong shear flow. We study this interesting phenomenon by pointwise flow-induced birefrigence (FIB) measurements in a well-known aqueous surfactant system, cetylpyridinium chloride/sodium salicylate. The dynamic nature of the local rheo-optical properties, such as birefringence and extinction angle across the gap of a Couette cell, were investigated over a range of shear rates, in particular the stress plateau region where shear stress is nearly independent of shear rate. This is probably the first application of point-wise FIB for the investigation of shear banding. The variation of optical signals along the radial direction of the Couette cell indicates that the fluid becomes inhomogeneous and forms bended structures, with either two bands or three bands across the gap, depending on the applied nominal shear rate. (c) 2005 The Society of Rheology.