Non-local effects in the shear banding of a thixotropic yield stress fluid

TL;DR

This paper introduces a non-local model to explain a new type of shear banding in thixotropic yield-stress fluids, supported by experimental rheo-MRI data, highlighting the role of non-local effects and thixotropy.

Contribution

The paper presents a simple non-local shear banding model that captures the continuous variation of shear rate and quantifies cooperativity length in microgel suspensions.

Findings

The model accurately fits rheo-MRI measurements.

The cooperativity length matches the microgel aggregate size.

A novel shear banding behavior due to non-local effects is observed.

Abstract

We observe a novel type of shear banding in the rheology of thixotropic yield-stress fluids that is due to the coupling of both non-locality and thixotropy. The latter is known to lead to shear banding even in homogeneous stress fields, but the bands observed in the presence of non-local effects appear different as the shear rate varies continuously over the shear band. Here, we introduce a simple non-local model for the shear banding (NL-SB), and we implement it for the analysis of micron-scale rheo-MRI velocimetry measurements of a milk microgel suspension in a cone-and-plate geometry. The proposed NL-SB model accurately quantifies the cooperativity length and yields values in the order of the aggregate size in the microgel.