(79a) Shear Induced Phase Separation (SIPS) with Shear Banding In Solutions of Cationic Surfactant and Salt

The rheological behavior and microstructure of branched, cationic worm like micellar (WLM) solutions of 40 mM erucyl bis(hydroxyethyl)methylammoniumchloride (EHAC) is studied as a function of added salt (sodium salycilate) concentration, temperature, and shear rate via Rheo-Small-Angle Light Scattering (Rheo-SALS). These WLM solutions exhibit shear induced phase separation (SIPS), manifested as visual turbidity under shear and the appearance of a characteristic “butterfly” scattering pattern in Rheo-SALS experiments. Flow kinematics measurements in a Couette geometry are used to determine the relationship between SIPS and shear banding i.e., the splitting of the viscometric flow into shear bands with different local shear rates. Modeling using the Giesekus constitutive equation provides a quantitative discrimination between banding and non-banding solutions. The combination of Rheo-SALS, dynamic rheology, velocimetry, and constitutive equation modeling allows detailed exploration of the relationship between SIPS, shear banding, fluid microstructure and the equilibrium phase behavior. SIPS is shown to be a necessary, but not sufficient condition for shear banding in branched WLMs.