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Monday, August 20, 2012
2:00 PM - 3:00 PM
CNLS Conference Room (TA-3, Bldg 1690)


Transient Shear Banding in Time-dependent Fluids

Xavier Illa
University of Bacelona, Spain

Simple Yield Stress Fluids [1] are a kind of complex fluids which do not show thixotropy, and therefore are expected to have a monotonic intrinsic flow curve, thus having a steady state without shear bands. However, recent experiments display shear banding during the transient state [2] indicating a time-dependent behavior. We study the dynamics of shear-band formation using a simple rheological model. The description couples the local structure and viscosity to the applied shear stress. We consider the Couette geometry, where the model is solved iteratively with the Navier-Stokes equation to obtain the time-evolution of the local velocity and viscosity fields. It is found that the underlying reason for dynamic effects is the non-homogeneous shear distribution, which is amplified due to a positive feedback between the flow field and the viscosity response of the shear thinning fluid. This offers a simple explanation for the recent observations of Transient Shear Banding in time-dependent fluids. [1] Ragouilliaux et al, Phys. Rev. E 76, 051408 (2007) [2] Divoux et al, Phys. Rev. Lett. 104, 208301 (2010).

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