Wall slip, shear banding, and instability in the flow of a triblock copolymer micellar solution

Abstract

The shear flow of a triblock copolymer micellar solution (PEO--PPO--PEO Pluronic P84 in brine) is investigated using simultaneous rheological and velocity profile measurements in the concentric cylinder geometry. We focus on two different temperatures below and above the transition temperature $T_c$ which was previously associated with the apparition of a stress plateau in the flow curve. (i) At $T=37.0^{\circ }$C $<T_c$, the bulk flow remains homogeneous and Newtonian-like, although significant wall slip is measured at the rotor that can be linked to an inflexion point in the flow curve. (ii) At $T=39.4^{\circ }$C $>T_c$, the stress plateau is shown to correspond to stationary shear-banded states characterized by two high shear rate bands close to the walls and a very weakly sheared central band, together with large slip velocities at the rotor. In both cases, the high shear branch of the flow curve is characterized by flow instability. Interpretations of wall slip, three-band structure, and instability are proposed in light of recent theoretical models and experiments.

arXiv comment13 pages, 13 figures

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• Shear banding in time-dependent flows of polymers and wormlike micelles
• Taylor-like vortices in the shear-banding flow of giant micelles
• The interplay between boundary conditions and flow geometries in shear banding: hysteresis, band configurations, and surface transitions
• Triggers and signatures of shear banding in steady and time-dependent flows
• Local Oscillatory Rheology from Echography
• Surfactant micelles: model systems for flow instabilities of complex fluids
• Shear banding in large amplitude oscillatory shear (LAOStrain and LAOStress) of polymers and wormlike micelles
• Interplay of edge fracture and shear banding in complex fluids
• Shear Banding from lattice kinetic models with competing interactions
• Wall slip and bulk flow heterogeneity in a sludge under shear