Polygonal Wrinkles in a Soft Solidified Droplet

The widespread occurrence of liquid freezing has profound implications for materials science, advanced manufacturing, and the global climate. Emerging from the intricate interplay of fluid dynamics, heat transfer, and phase change, recently, a captivating array of artistic and elegant patterns has been revealed. However, the solidified liquid component generally displays a pronounced resistance to deformation, thereby hindering the critical mechanical coupling inherently associated with thin films and soft materials. In this study, by investigating a hexadecane droplet impacting an aluminum substrate under strong supercooling conditions, we observe that this soft solidified droplet undergoes self-folding, followed by polygonal wrinkling due to Gauss's theorema egregium. These polygonal wrinkles of the submillimeter-thin film experience a striking sequential morphological transformation, characterized by a diminishing edge number, transitioning from octagonal to heptagonal, ultimately culminating in a tetragonal configuration. Both scaling analysis and numerical simulations demonstrate excellent agreement with the observed polygonal wrinkles.