Shear banding and interfacial instability in planar Poiseuille flow

TL;DR

This paper investigates the stability of shear banding interfaces in planar Poiseuille flow, revealing that flat interfaces are unstable and lead to complex flow patterns, with implications for experiments in rheology and microfluidics.

Contribution

It provides a theoretical analysis of interfacial instability in shear banded flows within a planar geometry, including growth rates and flow pattern predictions.

Findings

Flat shear band interfaces are unstable to undulations.

Unstable modes grow with specific wavevectors and rates.

Predicted flow patterns align with experimental observations.

Abstract

Motivated by the need for a theoretical study in a planar geometry that can easily be implemented experimentally, we study the pressure driven Poiseuille flow of a shear banding fluid. After discussing the "basic states" predicted by a one dimensional calculation that assumes a flat interface between the bands, we proceed to demonstrate such an interface to be unstable with respect to the growth of undulations along it. We give results for the growth rate and wavevector of the most unstable mode that grows initially, as well as for the ultimate flow patterns to which the instability leads. We discuss the relevance of our predictions to the present state of the experimental literature concerning interfacial instabilities of shear banded flows, in both conventional rheometers and microfluidic channels.