On the shear thickening flow of dilute CTAT worm-like micellar solutions

Dilute solutions of worm-like micelles exhibit shear thickening caused by microstructural changes under specific flow conditions. In this work, for the first time, shear thickening in parallel plate and Poiseuille flows is investigated using simultaneously particle image velocimetry (PIV) and theometry. Four distinctive zones of flow behavior are identified in parallel plates as the shear rate increases, namely, a Newtonian region, a transition regime where inhomogeneous nucleation of the shear-induced structures (SIS) is followed by homogeneous nucleation of SIS, and an apparent second-Newtonian regime at high shear rates, where rapid temporal fluctuations of the viscosity are smoothed out by inertia of the moving plate. In pipe pressure flow, PIV results reveal a flow pattern consisting of a superposition of two parabolic regions of the velocity profile located near the center and close to the pipe walls, and a transition region where again strong fluctuations in the velocity profile are observed. The experimental results are compared with predictions of a convected Maxwell constitutive equation coupled to a kinetic equation that accounts for an increase in dissipation of the system due to the presence of the SIS. The model accounts for the average steady values of the viscosity in the structured thickened state. (C) 2003 The Society of Rheology.