J. Phys. II France
Volume 7, Numéro 3, March 1997
Page(s) 459 - 472
DOI: 10.1051/jp2:1997138
J. Phys. II France 7 (1997) 459-472

Inhomogeneous Flows of Complex Fluids: Mechanical Instability Versus Non-Equilibrium Phase Transition

Grégoire Porte, Jean-François Berret and James L. Harden

Groupe de Dynamique des Phases Condensées, Case 026, Université Montpellier 11, 34095 Montpellier Cedex 05, France

(Received 1 August, 1996, received in final form 28 November 1996, accepted 5 December 1996)

We briefly review and re-interpret recent experimental results on shear-induced inhomogeneous flows in complex fluids. These are usually explained in terms of a mechanical instability of the non-linear flow regime. However, in at least two respects, the robustness of the two-state banded-flow regime and the kinetics of band formation under shear, they present striking analogies with ordinary field-induced phase transitions in equilibrium systems. We propose a phenomenological explanation of these effects in terms of an effective non-equilibrium potential that accounts for the free energy stored in a viscoelastic material under steady-shear conditions. Within this picture, a shear-thinning non-homogeneous flow can be shown to be a manifestation of some underlying hidden structural transition.

© Les Editions de Physique 1997