Coexistence of solid and liquid phases in impacting colloidal drops

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 ultrahigh-speed imaging and the free-surface geometry in drop impact to study the flow of colloidal suspensions, and for the first time observe coexisting solid and liquid phases. 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 travelling 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. 1 ar X iv :2 11 1. 10 86 8v 3 [ co nd -m at .s of t] 2 2 M ar 2 02 2