# Large-Scale Fabrication of Graded Convex Structure for Superhydrophobic Coating Inspired by Nature
## 3 Results and Discussion
### Durability and Chemical Stability of the Superhydrophobic Coating  
When applied in practice, the superhydrophobic coating is usually exposed to a relatively complex and difficult environment. With the accumulation of mechanical damage and chemical corrosion, it may lose its superhydrophobic properties. A series of methods were implemented in order to measure the durability of the P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) superhydrophobic coating, such as the washing test, sandpaper friction and ultraviolet light irradiation. After 100 sandpaper-rubbing cycles, the superhydrophobic filter paper coated with P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) still showed excellent superhydrophobic properties, with a CA of 146.3\({}^{\circ}\) and satisfactory water resistance. Encouragingly, in severely worn areas, the water droplets were still nearly  
Figure 4: Atomic-force microscopy 3D and 2D images of (**a**,**b**) adhesive-coated filter paper and (**c**,**d**) P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) adhesive-coated filter paper. spherical (Figure 7a). These results show that the superhydrophobic coating is durable and has excellent abrasion resistance. The durability of the superhydrophobic coating was evaluated by continuous UV-light irradiation, and it was found that the CA was 153.4\({}^{\circ}\) after 96 h of continuous UV-light irradiation, indicating that the P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) superhydrophobic coating has excellent UV-aging resistance (Figure 7b). The washing durability was also tested by recording the CA fluctuation of the superhydrophobic coating of the P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) coating in different washing cycles (Figure 7c). As a result, the CA decreased slowly with the increase in number of washes times and was maintained at 145.2\({}^{\circ}\) after 40 washes, which indicates that the P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) superhydrophobic coating has excellent washing durability, which is due to the excellent stability of PDVB with a crosslinked structure to various extreme conditions. Figure 5: **(a)** CA of the superhydrophobic paper coated by one of P\({}_{40}\), P\({}_{4}\), and P\({}_{0.4}\), **(b)** CA of the superhydrophobic paper coated by two of the three particles, and **(c)** CA of the superhydrophobic paper coated by three particles. Figure 6: **(a)** Photographs of the non-wetting of common droplets (milk, coffee, green tea, water and ink) on superhydrophobic coatings, **(b)** silver-mirror-reflection phenomenon of superhydrophobic coating soaked in water, **(c)** photograph of a stream of water jumping on the superhydrophobic coating, and **(d)** the images illustrate a water droplet (R\({}_{0}\approx 3\) mm) bouncing on the coating. Time interval is 30 ms.  
Figure 7: **(a)** CA variations of the P\({}_{40}\)–P\({}_{4}\)–P\({}_{0.4}\) superhydrophobic paper with attrition cycles, **(b)** CA variations of the P\({}_{40}\)–P\({}_{4}\)–P\({}_{0.4}\) superhydrophobic paper with UV irradiation time, **(c)** CA and SA of the P\({}_{40}\)–P\({}_{4}\)–P\({}_{0.4}\) superhydrophobic coating during 0–50 washing cycles, and **(d)** CA of the P\({}_{40}\)–P\({}_{4}\)–P\({}_{0.4}\) superhydrophobic coating soaked in several corrosive solutions. (The inset is a photo of water droplets and contact angle after various treatments). In different surroundings (for instance, common liquids), the potential deterioration of the superhydrophobic coating is due to the weakening of the bonding strength between the superhydrophobic surface and the substrate. The corrosion resistance of the P40-P4-P0.4 superhydrophobic coating was evaluated in various solutions. The prepared superhydrophobic coating was immersed in strong acid, milk, coffee, green tea, and strong alkali solutions for 24 h, followed by measurement. As shown in Figure 7d, after immersion in various solutions for 24 h, the CA decreased slightly and remained above 150\({}^{\circ}\). It can be concluded that the prepared P40-P4-P0.4 superhydrophobic coatings have excellent stability and chemical resistance.