Interface dynamics in shear-banding flow of giant micelles

TL;DR

This paper investigates the complex interface dynamics during shear banding in giant micelles, revealing multiple regimes of instability, interface migration, and pattern formation through combined mechanical and optical measurements.

Contribution

It provides detailed experimental insights into the stages of interface formation, migration, and destabilization in shear-banding flows, highlighting three distinct dynamic regimes and the three-dimensional nature of the flow.

Findings

Interface instability occurs along the stress plateau.

Pattern wavelength increases with control parameter.

Three dynamic regimes identified: oscillating, propagative, and chaotic.

Abstract

We report on a non trivial dynamics of the interface between shear bands following a start-up of flow in a semi-dilute wormlike micellar system investigated using a combination of mechanical and optical measurements. During the building of the banding structure, we observed the stages of formation, migration of the interface between bands and finally the destabilization of this interface along the vorticity axis. The mechanical signature of these processes has been indentified in the time series of the shear stress. The interface instability occurs all along the stress plateau, the asymptotic wavelength of the patterns increasing with the control parameter typically from a fraction of the gap width to about four times the gap width. Three main regimes of dynamics are highlighted : a spatially stable oscillating mode approximately at the middle of the coexistence region flanked by two ranges where the dynamics appears more exotic with propagative and chaotic events respectively at low and high shear rates. The distribution of small particles seeded in the solution strongly suggests that the flow is three-dimensional. Finally, we demonstrate that the shear-banding scenario described in this paper is not specific to our system.