# Large-Scale Fabrication of Graded Convex Structure for Superhydrophobic Coating Inspired by Nature
## 3 Results and Discussion  
### Chemical Analysis, Morphology and Wettability  
Figure 1 shows the infrared spectrum of the PDVB nanoparticles. The peak at 3054 cm\({}^{-1}\) in Figure 1 corresponds to the stretching vibration of the C-H bond on the benzene ring, which is the characteristic peak of the benzene ring. The peaks at 1509 cm\({}^{-1}\), 1486 cm\({}^{-1}\), and 1451 cm\({}^{-1}\) correspond to the stretching vibration of the benzene-ring skeleton. The peak at 3018 cm\({}^{-1}\) corresponds to the stretching vibration of the C-H bond of vinyl, which is the characteristic peak of vinyl. The peaks at 2929 cm\({}^{-1}\) and 2869 cm\({}^{-1}\) correspond to the antisymmetric and symmetric stretching vibrations of the C-H bond of the methylene group. The peak at 1605 cm\({}^{-1}\) corresponds to the stretching vibration of the vinyl C=C bond. This is the characteristic peak of methylene [29]. The existence of this series of peaks indicates that the polydivinylbenzene material was successfully synthesized by the hydrothermal method. Figure 2 reveals the SEM images and size distribution of the P\({}_{40}\), P\({}_{4}\), and P\({}_{0.4}\) PDVB-NP\({}_{5}\). Obviously, the combined solvothermal reaction and ultrasonic disintegration did indeed produce nanoparticles (Figure 2a,c,e). Figure 2b,d,f depict the size distribution of the PDVB-NPs, in which two main peaks exist: the smaller peak is less than 100 nm, while the larger peak is greater than 500 nm. In other words, the larger peak indicates the PDVB-NPs cluster, and the smaller peak may indicate the size distribution of PDVB-NPs. Based on the smaller peak, we obtained average particle sizes of 81.5, 40.3, and 12.7 nm corresponding to P\({}_{40}\), P\({}_{4}\), and P\({}_{0.4}\), respectively. The peaks of the PDVB-NPs clusters at 1200, 760, and 900 nm correspond to P\({}_{40}\), P\({}_{4}\), and P\({}_{0.4}\), respectively. It is clear that the combination of solvothermal treatment and sonication does produce nanoparticles and micro-scale clusters, which is the key to the superhydrophobicity of the coating. For the purpose of determining the effect of different mass ratios of PDVB-NP\({}_{5}\) on the surface morphology of the superhydrophobic PDVB coatings, the morphologies of the filter paper coated with adhesive and the P\({}_{40}\)-coated filter paper (P\({}_{40}\) particle content was 3 wt%) were studied. Filter paper coated with P\({}_{40}\)-P\({}_{4}\) (based on the total content of 3 wt%, the mass ratio of P\({}_{40}\) and P\({}_{4}\) was 1:1) and filter paper coated with P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) (The mass ratio of P\({}_{40}\), P\({}_{4}\) and P\({}_{0.4}\) particles was 1:1, based on the total content of 3 wt%) was studied through  
Figure 1: FTIR spectra of PDVB-NP\({}_{5}\). Because surface roughness is the primary factor in constructing a superhydrophobic surface, the surface roughness of P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) superhydrophobic coating was further characterized by AFM. In Figure 4a,b, the surface of the adhesive-coated filter paper is very smooth, with a root-mean-square roughness (Rq) of 1.31 nm. The Rq value is usually used to quantitatively evaluate roughness; the higher the Rq value, the greater the roughness. Unlike the adhesive-coated filter paper, the P\({}_{40}\)-P\({}_{4}\)-P\({}_{0.4}\) adhesive-coated filter paper that was made from PDVB-NPs with different particle diameters shows a rougher profile and the shaped protrusion structure varies greatly in height (Figure 4c,d). The calculated Rq value is 65.2 nm. It is believed that the mountain-shaped convex structure traps the air in the grooves between the peaks, thereby forming a stable air layer. As the contact area between the water droplets and the coating surface is reduced, a hydrophobic surface with low adhesion is produced. In this paper, CA is used as the main indicator to measure the hydrophobic performance of the coating.