Coexistence of solid and liquid phases in shear jammed colloidal drops

TL;DR

This study uses high-speed imaging to reveal how colloidal suspensions can exhibit coexisting solid and liquid phases during shear jamming caused by impact, highlighting localized shear jamming patches and front propagation.

Contribution

First direct visualization of shear jamming in colloidal drops showing coexistence of phases and dynamic front propagation during impact.

Findings

Observation of coexisting solid and liquid phases due to shear jamming

Identification of a solidification front traveling from impact point

Front speed depends on impact conditions relative to shear thickening transition

Abstract

Complex fluids exhibit a variety of exotic flow behaviours under high stresses, such as shear thickening and shear jamming. Rheology is a powerful tool to characterise these flow behaviours over the bulk of the fluid. However, this technique is limited in its ability to probe fluid behaviour in a spatially resolved way. Here, we utilise high-speed imaging and the free-surface geometry in drop impact to study the flow of colloidal suspensions. We report, for the first time, observations of coexisting solid and liquid phases due to shear jamming caused by impact. In addition to observing Newtonian-like spreading and bulk shear jamming, we observe the transition between these regimes in the form of localised patches of jammed suspension in the spreading drop. We capture shear jamming as it occurs via a solidification front traveling from the impact point, and show that the speed of this front is set by how far the impact conditions are beyond the shear thickening transition.