Liquid encapsulation in a freezing sessile drop

During the solidification of a sessile drop, the effect of heat exchange from the gaseous environmental medium is generally ignored. However, by combining experimental observations, direct numerical simulations, and a theoretical model, we have demonstrated that the environmental medium, particularly one with high thermal conductivity such as a liquid, has nonnegligible heat exchange with both the drop and the substrate, leading to accelerated cooling of the outer surface of the sessile drop. Consequently, it causes alterations in the geometry of the freezing front and ultimately results in the formation of a solidified shell that encloses the drop. Furthermore, the encapsulated liquid continues to solidify, which induces volume change and consequently changes the final outcome of the freezing process. This study highlights the importance of considering the properties of the environmental medium and provides novel strategies to manipulate the freezing rate and reshape the morphology of the solidified drop.