Self-Lifting Droplet Driven by the Solidification-Induced Solutal Marangoni Flow.

Multicomponent droplets are pertinent to diverse applications ranging from 3D printing to fabrication of electronic devices to medical diagnostics and are typically inherent with the occurrence of the phase transition in the manifestation of evaporation and solidification. Indeed, the versatile transformations and fascinating morphologies of the droplets have been identified, which primarily arise from the evaporation-induced flow. Here, we report the self-lifting behavior of a frozen binary droplet, resulting in a nearly doubling in height, in a fashion that defies against the gravitational effect. This counterintuitive observation is attributed to an internal solutal Marangoni flow up to 1  mm/s, which is driven by the enriched solute concentration locally in the vicinity of the solidification front. Moreover, we perform theoretical analysis by incorporating the propagation of solidification front, and the calculated spatiotemporal evolution of droplet shape agrees with experiments excellently. The effects of several key physical parameters on self-lifting are elucidated quantitatively, providing guidance to control the self-lifting. These results will further advance our understanding of underlying physicochemical hydrodynamics in the multicomponent liquid systems subjected to heat transfer and phase change, consequently shedding light on the relevant technological applications.