Inhomogeneous structure formation and shear-thickening in worm-like micellar solutions

Abstract

The time evolution of flow-induced structures in low-concentration worm-like micellar solutions is studied using direct visualization and rheological methods. The visualization measurements show growth of a new viscous shear-induced phase (SIP) starting on the inner wall of a Couette shear cell at a time t1 after the commencement of shear flow. The SIP continues to grow across the shear cell until it fills the entire gap at a time t2. Rheological measurements show that the time t1 corresponds to the induction time for the increase in stress and that t2 corresponds to the plateau time for the saturation of stress. These measurements provide convincing evidence that the increase of stress with time results from the inhomogeneous growth of a new shear-induced phase in the flow cell. The growth of the new phase across the cell is approximately linear in time. (*) Permanent address: Laboratoire d'Ultrasons et de Dynamique des Fluides Complexes, URA au CNRS no. 851, Université Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg, France. © Les Editions de Physique.