Spatio-temporal oscillations and rheochaos in a simple model of shear banding

TL;DR

This paper investigates a simple shear banding model revealing complex oscillatory and chaotic flow behaviors driven by flow-microstructure coupling, with results aligning with experimental observations of fluctuating shear bands.

Contribution

It introduces a minimal model capturing rich spatio-temporal oscillations and rheochaos in shear banding, advancing understanding of flow instabilities in complex fluids.

Findings

Identification of pulsating shear bands near walls at low shear rates.

Observation of high shear pulses ricocheting across the flow cell.

Detection of oscillating bands and defect interactions at high shear rates.

Abstract

We study a simple model of shear banding in which the flow-induced phase is destabilised by coupling between flow and microstructure (wormlike micellar length). By varying the strength of the instability and the applied shear rate, we find a rich variety of oscillatory and rheochaotic shear banded flows. At low shear and weak instability, the induced phase pulsates in width next to one wall of the flow cell. For stronger instability, single or multiple high shear pulses ricochet across the cell. At high shear rates we observe oscillating bands on either side of a defect. In some cases, multiple such defects exist and propagate across the cell to interact with each other. We discuss our results in the context of recent observations of oscillating and fluctuating shear banded flows.