Marangoni-driven freezing dynamics of supercooled binary droplets*

Solidification of droplets is of great importance to various technological applications, drawing considerable attention from scientists aiming to unravel the fundamental physical mechanisms. In the case of multicomponent droplets undergoing solidification, the emergence of concentration gradients may trigger significant interfacial flows that dominate the freezing dynamics. Here, we experimentally investigate the fascinating snow-globe freezing dynamics of supercooled ethanol-water droplets. We reveal that these unique freezing dynamics are driven by solidification-induced solutal Marangoni flow within the droplets. We quantitatively characterize the concentration-dependent migration and growth dynamics of ice particles, tightly connecting them to the solutal Marangoni effect and the associated convective heat transfer. Moreover, we show that the final wrapping state of droplets can be modulated by the concentration of ethanol. Our findings may pave the way for novel insights into the physicochemical hydrodynamics of multicomponent liquids undergoing phase transitions.