## 3 Results and Discussion  
### Surface Morphology and Composition  
As we all know, the wettability of a solid surface is determined by the geometric microstructure and chemical composition of the surface [20]. Due to the presence of many hydroxyl groups, the surface of nano-SiO\({}_{2}\) particles is hydrophilic. In addition, its surface energy is relatively high, which easily leads to agglomeration of SiO\({}_{2}\) nanoparticles. Fluorosilane can effectively modify hydroxyl-rich surfaces, thereby reducing the surface energy of solids [21]. Figure 1 shows the FTIR spectra of unmodified SiO\({}_{2}\) and PFOTES-SiO\({}_{2}\). Compared with the infrared spectrum of unmodified SiO\({}_{2}\), the characteristic peaks of 1120, 702 and 660 cm\({}^{-1}\) appear in PFOTES-SiO\({}_{2}\). This is attributed to the stretching vibration of CF, CF\({}_{2}\) or CF\({}_{3}\)[22], indicating that PFOTES has successfully modified SiO\({}_{2}\) nanoparticles [21]. The influence of the mass ratio of PFOTES-SiO\({}_{2}\) to PVDF on the wettability is investigated. The surface wettability of PVDF/PFOTES-SiO\({}_{2}\) coatings with different mass ratios is tested with a contact angle measuring instrument, and the results are shown in Figure 2. Figure 2a shows the effect of PFOTES-SiO\({}_{2}\) content on wettability (the amount of PVDF is determined to be 0.3 g). It can be seen from Figure 2a that when the coating contains only PVDF, the contact angle is 97.2\({}^{\circ}\). As the content of PFOTES-SiO\({}_{2}\) in the coating increases, the contact angle continues to increase. When the content of PFOTES-SiO\({}_{2}\) is 0.10 g, the contact  
Figure 1: FTIR spectra of (a) SiO\({}_{2}\), (b) PFOTES–SiO\({}_{2}\). angle reaches the maximum value of 163.1\({}^{\circ}\). However, with the increase of PFOTES-SiO2, the contact angle began to decrease, but it remained greater than 150\({}^{\circ}\). This is because the increase of hydrophobic nanoparticles increases the roughness of the coating and reduce the surface energy, thereby improving the hydrophobicity of the magnesium alloy surface. However, with the excessive content of nanoparticles, PVDF as a film-forming agent cannot effectively combine the nanoparticles, thereby reducing the uniformity of the dispersion of nanoparticles in the coating, thus reducing the wettability of the coating surface. When the content of nanoparticles is excessive, PVDF as a film-forming agent cannot effectively bond the nanoparticles, thereby reducing the uniformity of the dispersion of nanoparticles in the coating, and thus reducing the wettability of the coating surface. Figure 2b shows the effect of PVDF content in the coating on the surface wettability (the amount of PFOTES-SiO2 is determined to be 0.1 g). It can be seen that the contact angle in the coating increases first and then decreases with the increase of PVDF content. When the PVDF content is 0.3 g, the contact angle (CA) reaches the maximum value (163.1\({}^{\circ}\)). This is because when the PVDF content is low, PVDF cannot completely disperse the PFOTES-SiO2 in the coating during the phase separation and film formation process, resulting in the coating contact angle being less than 150\({}^{\circ}\). As the content of PVDF increases, PVDF can wrap the entire nanoparticles, so the surface contact angle continues to increase. When the content of PVDF is too much (m(PVDF) > 0.5 g), the spraying solution is too viscous, resulting in uneven dispersion of the solution during the preparation process, thus reducing the hydrophobic performance. As mentioned above, by adjusting the mass of PVDF to PFOTES-SiO2 in the coating, a suitable surface microstructure can be obtained, thereby obtaining a stable superhydrophobic coating. Based on the results of water contact angle tests, the optimal value of coating preparation is obtained (m(PVDF) = 0.3 g and m(PFOTES-SiO2) = 0.1 g), so that the superhydrophobic surface prepared based on the optimal value is studying in stability performance, corrosion performance, etc.