# A Review on Ultrafast Laser Enabled Excellent Superhydrophobic Anti-Icing Performances
## 3 Anti-Icing Mechanisms of SHSs
### Failure Factors of Superhydrophobic Anti-Icing Surfaces
#### 3.2.3 Environmental Adaptivity  
Numerous complex and unexpected disturbances exist in practical application environments, including high-speed droplet impact, dust accretion, strong wind, etc. [124]. In this case, superhydrophobic anti-icing surfaces fail more easily compared to static laboratory environments. We take the common dynamic impact as an example to elucidate the influences of environments on anti-icing properties. Figure 10a,b show the comparison of four typical dynamic tests: water jet impacting, solid particle impacting, supercooled droplet impinging, and icing wind tunnel tests [81]. It can be observed that there are tremendous differences for different test conditions. For icing wind tunnel tests (a widely adopted method to simulate real aviation environments), the droplet sizes and impacting velocities are generally in the range of \(\sim\)20-100 \(\upmu\)m and \(\sim\)10-100 m/s. The dynamic pressures in icing wind tunnel tests reach up to over 1 Mpa, which is more than an order of magnitude higher than those in other tests. Under continuous, high-speed, high-pressure and tiny droplet impact, superhydrophobic anti-icing surfaces tend to fail extremely easily. Figure 9: Two key factors influencing surface durability. (**a**) Surface structure types (Reproduced with permission from [118]. Copyright (2023) Royal Society of Chemistry.) (**b**) Low-surface-energy coatings (Reproduced with permission from [122]. Copyright (1999) American Chemical Society.) Figure 10c shows the icing processes of the superhydrophobic anti-icing surfaces fabricated by the DLIP. The surfaces, which could easily repel supercooled droplets (\(-5\)\({}^{\circ}\)C; diameter: \(\sim\)2 mm; impact speed: 3.4 m/s) at the substate temperature of \(-25\)\({}^{\circ}\)C, not only failed in 0.5 min in the icing wind tunnel tests but also even resulted in more ice accretion than pristine smooth surfaces. We ascribed the phenomenon to the preferentially bottom freezing when supercooled tiny droplets contacted surfaces. Within several milliseconds, the ice embryo nucleated and generated a strong adhesion to the substrate instead of rebounding (Figure 10d). Meanwhile, subsequent high-pressure droplets continuously impacted the surfaces to further increase the ice adhesion and lead to ice accretion. To ensure that superhydrophobic anti-icing surfaces have qualified environmental adaptivity, [PERSON] et al. explored the design rules of ULSASs by testing various micro-nanostructures in icing wind tunnel conditions [125]. Two dominant but opposite factors  
Figure 10: Influence of environmental disturbances on anti-icing performances. (**a**) Summarization of the relationships between the size of the droplets/particles and the impacting velocity from the four dynamic experiments: water-jet impacting, solid-particle impacting, supercooled-droplet impinging, and icing wind tunnel tests. (**b**) Dynamic impact pressure when the droplets/particles contact the target surfaces. (**c**) Image sequences of the icing processes on SHSs in icing wind tunnel tests. (**d**) Schematic diagrams showing the physical processes at dynamic impacting (Reproduced with permission from [81]. Copyright (2023) American Chemical Society.) (**e**) Comparison of structural sizes with droplet sizes. (**f**) Interfacial shear stress versus freezing fraction (Reproduced with permission from [125]. Copyright (2020) John Wiley and Sons.) were summarized: stress concentrations and surface contact area. They found that although micro-nanostructures with small sizes had a smaller solid-liquid contact area, the structures also induced lower stress concentration. For those with larger sizes, higher stress concentration but a larger contact area was produced. It was concluded that the laser-fabricated structures should be with a spatial period of one order of magnitude smaller than the mean volume diameter (MVD) and with abundant nanostructures (Figure 10e).