Three-dimensional frost structures on fluorine coated silver iodide (AgI) micropatterns

Frost growth on silver iodide (AgI) stripes micropatterned surfaces is determined not only by the initiation of nucleation, but also by its growth kinetics after nucleation. In this study, these effects are investigated by comparing frost growth on three surfaces: bare silicon, AgI stripes on silicon, and fluorinated AgI stripes with modified wettability. Two-dimensional (2D) observations combined with three-dimensional (3D) frost reconstruction by the replica method reveal distinct growth behaviors on the three surfaces. Bare Si undergoes condensation freezing, forming dense and vertically oriented frost columns. In contrast, uncoated AgI stripes promote quick ice nucleation and lateral growth, producing frost with approximately 25% less ice volume and a characteristic horizontal wedge-like structure. For the fluorine (F) coated surface, lateral propagation is suppressed and frost grows predominantly upward, resulting in an approximately 30% increase in frost accumulation and the formation of vertically oriented columnar structures connected to the substrate through slender frost roots. These results show that nucleation activity determines where frost initiates, whereas surface wettability regulates the direction of frost growth, clarifying the distinct roles of nucleation activity and surface wettability in controlling frost morphology.