# Large-Scale Fabrication of Graded Convex Structure for Superhydrophobic Coating Inspired by Nature
## 3 Results and Discussion
### Chemical Analysis, Morphology and Wettability
Figure 5a exhibits the relation between the particle content of P\({}_{40}\), P\({}_{4}\), and P\({}_{0.4}\) and the CA of the superhydrophobic surfaces. When the content of PDVB-NPs was different, the CA had a significant change from 95\({}^{\circ}\) to 152\({}^{\circ}\). The rapid increase in the CA on the superhydrophobic coating was due to the increase in surface roughness. It is worth noting that when the content of PDVB-NPs was 3 wt%, the optimal hydrophobicity reached 152\({}^{\circ}\). When the content of PDVB-NPs was less than or greater than 3 wt%, the CA was less than 152\({}^{\circ}\), indicating that PDVB-NPs had excessively accumulated on the surface. The content ratio of the three PDVB-NPs based on 3 wt% total content was studied in order to maximize the CA. Two kinds of PDVB-NPs were selected to prepare functionalized coatings, and the mass ratios were 1:3, 2:2, and 3:1, respectively. Under different combinations, when the mass ratio of the P\({}_{40}\)-P\({}_{0.4}\) coating was 1:3, the maximum CA was 156.2\({}^{\circ}\) (Figure 5b). This should be due to the construction of an effective hierarchical protruding structure on the surface and the proper collaboration of clusters of different sizes. After the three kinds of particles were blended with various mass ratios, the CA of the functionalized coating was further improved. When the three PDVB-NPs were mixed in different mass ratios, the minimum CA was 154\({}^{\circ}\) and the maximum CA was 160.1\({}^{\circ}\)  
Figure 2: SEM images and size distribution of PDVB-NPs with different mass ratios of DVB and AINB: (**a**,**b**) P\({}_{40}\), (**c**,**d) P\({}_{4}\), and (**e**,**f**) P\({}_{0.4}\). (Figure 5c). The improved CA and SEM results were in good agreement, indicating that the composite of PDVB particles of various sizes had a key effect on the wettability of the coating. By adjusting the mass ratio of the PDVB-NP\({}_{\text{S}}\) with different diameters, the best superhydrophobicity was obtained, and the lotus-leaf-like micro-nano multi-level protruding structure was successfully built on the surface. Figure 3: Micromorphology and CA of (**a**) adhesive-coated filter paper, (**b**) P\({}_{40}\)-coated filter paper, (**c**) P\({}_{40}\)-P\({}_{4}\)-coated filter paper, (**d**) P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\)-coated filter paper. In order to test the waterproof capability in actual application, the water droplets are almost spherical on the P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) superhydrophobic coating (Figure 6a). When the superhydrophobic coating was immersed in water, bubbles trapped by the micro-nano rice structure appeared on the surface of the coating. Attractively, because an air layer was trapped on the coating, an obvious silver-mirror phenomenon appears (Figure 6b). As the contact area between the coating and the water droplets was reduced, the air layer effectively blocked the coating after wetting. Even if high-speed water spray is sprayed onto the surface of the coating, the water can easily bounce off the coating (Figure 6c), which further proved the strong superhydrophobic properties of the coating. According to the Cassie-Bacchus law [30; 31], this excellent non-wettability is due to the low adhesion of water which was caused by the air pockets captured by the micro-nano structure, which made it easy for water droplets to fall onto the superhydrophobic surface. Figure 6d shows the water-drop-bounce test. A 30 \(\upmu\)L water droplet made a free fall motion from a height of 40 mm from the coating. After dropping onto the superhydrophobic coating, it quickly bounced, indicating that the superhydrophobic coating had extremely low water adhesion and impact resistance. It further proved the analysis results of the sputtering test of the water column on the superhydrophobic surface (Figure 6c). The impact resistance comes from the buffering and dispersing effect of the micro-nano convex structure on the impact force, and the low water adhesion is conducive to the efficient self-cleaning of the coating.