Flow-Switched Bistability in a Colloidal Gel with Non-Brownian Grains

TL;DR

This study reveals that adding non-Brownian grains to a colloidal gel induces flow-switched bistability, where shear conditions determine whether the gel liquefies or forms a yield-stress state, creating a new mechanorheological material.

Contribution

It introduces a novel flow-switched bistability in colloidal gels with granular inclusions, supported by experimental mapping and demonstration across different particle and solvent systems.

Findings

Prolonged shear causes gel liquefaction into globules.

Fast shear results in a yield-stress gel with granular inclusions.

Behavior is consistent across different particle and solvent mixtures.

Abstract

We show that mixing a colloidal gel with larger, non-Brownian grains generates novel flow-switched bistability. Using a combination of confocal microscopy and rheology, we find that prolonged moderate shear results in liquefaction by collapsing the gel into disjoint globules, whereas fast shear gives rise to a yield-stress gel with granular inclusions upon flow cessation. We map out the state diagram of this new `mechanorheological material' with varying granular content and demonstrate that its behavior is also found in separate mixture using different particles and solvents.