Characterization of droplet freezing on superhydrophobic surfaces with different microstructures

•Design of superhydrophobic surfaces with grooved microstructures.•The effect of structure spacing on the droplet freezing process was studied.•Droplet freezing shape change and freezing front growth were studied.•Larger structure spacing reduced surface delayed icing performance. Superhydrophobic surfaces with microstructures have garnered significant attention for anti-icing applications due to their lower cost and higher efficiency. In this paper, we designed and prepared surfaces with differently spaced groove microstructures on aluminum substrates using femtosecond laser technology combined with low-surface-energy coatings. In addition, droplet freezing times and freezing processes were investigated to study the anti-icing properties of different surfaces. The results demonstrated that the sample surfaces exhibit excellent superhydrophobicity. At the cold surface temperature of −15 °C, the freezing time of droplets on the surface with a spacing of 100 μm is 707.9 s, which is far more than that of other sample surfaces. Additionally, groove spacing has a more pronounced effect on the rate of change in height compared to the diameter before and after droplet freezing. During the freezing process, the freezing front initiates from the cold surface and grows upward in a convex shape. As the growth of the freezing front at the edge accelerates, it eventually becomes concave, and this phenomenon occurs earlier at lower temperatures. Freezing is considered complete when the freezing tip appears. As the temperature decreases, both the droplet supercooling time and phase change time shorten. This paper is anticipated to provide a reference for the design of efficient anti-icing materials.