Transient Shear Banding in Time-dependent Fluids

TL;DR

This paper investigates the formation and evolution of shear bands in time-dependent fluids using a coupled rheological model, explaining transient shear banding phenomena through feedback mechanisms in shear thinning fluids.

Contribution

It introduces a simple coupled model linking local structure, viscosity, and shear stress to explain transient shear banding in time-dependent fluids.

Findings

Shear banding arises from non-homogeneous shear distribution.

Positive feedback amplifies shear localization.

Model explains recent experimental observations of transient shear banding.

Abstract

We study the dynamics of shear-band formation and evolution using a simple rheological model. The description couples the local structure and viscosity to the applied shear stress. We consider in detail 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. Extensions to more complicated rheological systems are considered.