Manipulating the freezing direction of liquid via composite thermal patterns

It is natural that a water droplet freezes upward when deposited on a cold substrate, and a pointy tip forms at the center due to volume expansion during freezing. In this work, the local freezing direction can be changed via composite thermal patterns on a substrate, and the pointy tip of a frozen droplet can be avoided at the same time. Droplets freeze faster in the conductive regions than in the insulating areas. Consequently, the freezing direction and the morphology of the frozen droplet can be controlled by varying the insulating patterns on the substrate. Theoretical and experimental analyses were performed to investigate the effect of composite thermal patterns on the droplet freezing process and morphology. The findings of this work present an effective method for manipulating the anisotropic solidification process on cold substrates.