Thermally-gelling yield-stress drops impacting an immiscible liquid

We analyse, in this experimental and numerical work, the physical mechanisms governing the spreading and penetration of thermally gelling yield stress drops upon impact with an immiscible liquid. More specifically, a falling millimetric-70°C-agar drop (described as an elasto-viscoplastic fluid) passes through a 25°C-immiscible liquid/air interface and forms an air cavity, which later retracts, while the drop penetrates the immiscible liquid. The drop's temperature decreases within the liquid, which gives rise to a gelled elastic membrane in the outer part of the drop and ultimately turns the impacting object into a strong gel (solid-like material). Hence, during penetration, the drop undergoes both thermally induced solidification (gelation) and deformation (impact and penetration), leading to different final solid-like shapes depending on the impact velocity, gelation kinetics, drop/liquid hydrodynamic interactions, and the drop's rheological properties.

Work in collaboration with N. Nazzal (Mines Paris - PSL), M. Drahé (Mines Paris - PSL), R. El Khoury (Mines Paris - PSL), E. Peuvrel-Disdier (CNRS & Mines Paris - PSL), Loren Jørgensen (CNRS & ESPCI Paris - PSL), and C. Monteux (CNRS & ESPCI Paris - PSL).