Deforming Ice with Drops

A uniform solidification front undergoes nontrivial deformations when encountering an insoluble dispersed particle in a melt. For solid particles, the overall deformation characteristics are primarily dictated by heat transfer between the particle and the surrounding, remaining unaffected by the rate of approach of the solidification front. In this Letter we show that, conversely, when interacting with a droplet or a bubble, the deformation behavior exhibits entirely different and unexpected behavior. It arises from an interfacial dynamics which is specific to particles with free interfaces, namely, thermal Marangoni forces. Our Letter employs a combination of experiments, theory, and numerical simulations to investigate the interaction between the droplet and the freezing front and unveils its surprising behavior. In particular, we quantitatively understand the dependence of the front deformation Δ on the front propagation velocity, set by the strength of the applied thermal gradient, which, for larger front velocities (larger applied thermal gradients), can even revert from attraction (Δ<0) to repulsion (Δ>0).