## 3 Results and Discussion
### Stability and Wear Resistance of Superhydrophobic Surfaces  
The chemical stability of the superhydrophobic surface is a key factor that determines its feasibility in industrial applications. As a result, using an acid-based solution and air exposure method, the chemical stability of the obtained superhydrophobic surface was investigated. Figure 5a shows the contact angle and sliding angle of water droplets of different pH solutions to the superhydrophobic surface. The contact angle is maintained above 154\({}^{\circ}\) and the sliding angle is below 10\({}^{\circ}\) in the pH range of 1-14, indicating that acidity and alkalinity  
Figure 4: FTIR spectrum of PVDF/PFOTES–SiO\({}_{2}\) superhydrophobic surface. Figure 3: FESEM images of (**a**) the bare AZ31B Mg alloy and (**b**–**d**) the super-hydrophobic surface under magnifications. have little effect on the superhydrophobic properties of the prepared superhydrophobic coating. To investigate the change of surface wettability of superhydrophobic samples in the air, the prepared samples were exposed to air at a room temperature of 20-25\({}^{\circ}\) and relative humidity of 30-50%, and the contact angle and sliding angle was tested every 10 days, as shown in Figure 5b. It can be found that the superhydrophobic surfaces maintain good superhydrophobicity after exposing it to air for 60 days, the contact angle remains above 155\({}^{\circ}\), and the sliding angle remains below 5\({}^{\circ}\), indicating that the superhydrophobic surface has stability under air conditions [26; 27]. Figure 5c shows the contact angle and sliding angle of the superhydrophobic surface immersed in 3.5 wt % NaCl solution. The results show that the surface is still superhydrophobic after being immersed in 3.5 wt % NaCl for 7 days (contact angle is 155.2\({}^{\circ}\), sliding angle is 3.2\({}^{\circ}\)). Most applications superhydrophobic coatings are based on their repellence with aqueous solutions. The functional properties of the superhydrophobic coatings are usually characterized by the value of the contact angle produced by the droplets on the surface of these materials in a short period of time. However, if the superhydrophobic surfaces are used in the industrial field, it is necessary to study the characteristics and stability of the wetting behavior of the prepared superhydrophobic surface in long-term contact with an aqueous medium [14]. Therefore, the chemical durability of superhydrophobic surfaces to acidic, neutral, or alkaline aqueous solutions has been investigated by measuring the static water contact angle and sliding angle of the superhydrophobic surface before and after immersion in aqueous solutions of different pH values, and the results are shown in the Figure 6. After immersion in the acidic solutions at pH 4.0 and neutral aqueous at pH 7.0, the static water contact angles and sliding angle of the superhydrophobic surfaces decreases slightly as the immersion time increases. The static water contact angles decreased from 161.0\({}^{\circ}\) to 157.0\({}^{\circ}\) and from 162.2\({}^{\circ}\) to 159.8\({}^{\circ}\) within 120 min after immersion in the acidic solution and the neutral solution, respectively. And the sliding angle increased 2.4\({}^{\circ}\) and 0.2\({}^{\circ}\) in pH 4.0 solutions and pH 7.0 solutions, respectively. However, within immersion for 100 min in alkaline solutions (pH 10.0), the static water contact angles gradually decreased to 150.2\({}^{\circ}\). As the immersion time is further extended, the surface loses its  
Figure 5: The CA and the SA of the superhydrophobic surfaces (**a**) under pH value, (**b**) exposure to air, and (**c**) immersed in 3.5 wt % NaCl solution). superhydrophobicity. These results indicate that although the prepared superhydrophobic surface exhibits high chemical durability in neutral and acidic aqueous solutions, it has low chemical durability in alkaline aqueous solutions.