## 3 Results and Discussion
### Durability in Different Environments of Coatings  
The transmittance of coatings often decreases because of dust in practical applications. The coating with self-cleaning ability can effectively reduce the influence of dust on transmittance. Owing to being soaked in HMDS, the coating got the self-cleaning ability. Si-CH\({}_{3}\) in HMDS was transferred to the surface of the coating, making the surface hydrophobic. When the water droplet was dropped on the surface, the contact angle was up to 121\({}^{\circ}\), which is shown in Figure 7b. However, in Figure 7a, the contact angle of the unsoaked DETA-OSER was just 69\({}^{\circ}\), which was lower than the soaked one. It indicated that the hydrophobic groups were successfully grafted onto the surface. Additionally, this happened to MXDA-OSER. Generally, being soaked in the HMDS reduces the surface energy and increases the contact angle of water droplets, which endows the coating with self-cleaning ability. The durability of the coating is a key technical concern. In order to study its chemical stability in different environments, DETA-OSER and MXDA-OSER were soaked in pH = 2 and pH = 12 solutions, seawater (3.5% NaCl aqueous solution) and organic solvent (anhydrous acetone), respectively. According to Tables 3 and 4, DETA-OSER and MXDA-OSER showed to be insoluble in acetone because their polarity was weak owing to the large molecular chains. Besides, DETA-OSER and MXDA-OSER, to a certain extent, could resist the erosion of the acid and seawater, but the hardness of DETA-OSER decreased slightly. The possible reason is that the molecular chains with phenyl are more inert due to the steric hindrance of phenyl. In addition, both DETA-OSER and MXDA-OSER could be soaked in an aqueous alkali only for a short time. The reason for hardness decline is that the Si-O-Si framework reacts with NaOH to produce the soluble Na\({}_{2}\)SiO\({}_{3}\). Gradually, the corrosion of strong alkali destroyed the cross-link structure. Figure 6: Transmittance spectra of the DETA-OSER, MXDA-OSER and bare glass. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Refractive Index (\(\pm\)0.003)** & **Thickness** \\ \hline DETA-OSER & 1.493 & 103 nm \\ Bare glass & 1.512 & 700 μm \\ MXDA-OSER & 1.525 & 114 nm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Refractive index and thickness of the DETA-OSER, MXDA-OSER and bare glass. To study the thermal behavior of materials, the thermal-oxidative decomposition processes of samples were investigated. According to the DTG curves shown in Figure 8, a maximum value with 160 \({}^{\circ}\)C and 13.4 min was observed. When the temperature was lower than 160 \({}^{\circ}\)C, the water adsorbed on the surface and started to evaporate, and the free Si-OH and the unreacted C\({}_{2}\)H\({}_{5}\)-O-Si also began to condense to produce a Si-O-Si cross-link structure, which reduced the mass during this time. In other words, annealing at 160 \({}^{\circ}\)C made the cross-link more thorough and then increased the hardness of the coating. When the temperature was higher than 160 \({}^{\circ}\)C, the rate of mass decrease began to increase, which meant that the polymer coating began to decompose intensely. Therefore, the DETA-OSER coating has the highest working temperature of 160 \({}^{\circ}\)C. Similarly, a maximum value of 155 \({}^{\circ}\)C was obtained at 12.7 min for MXDA-OSER coating. Meanwhile, it is observed that the DTG curves fluctuated greatly in the high-temperature region (>160 \({}^{\circ}\)C). This was \begin{table}
\begin{tabular}{c c c c c} \hline  & **1 Day** & **3 Days** & **5 Days** & **7 Days** \\ \hline pH = 2 & 8H & 8H & 8H & 8H \\ pH = 12 & 8H & 3B & \textless{}6B & \textless{}6B \\ Seawater & 8H & 8H & 8H & 8H \\ Acetone & 8H & 8H & 8H & 8H \\ \hline \end{tabular}
\end{table} 
Table 4: The pencil hardness grade of MXDA-OSER being soaked in different solutions. Figure 7: Contact angle of a water droplet on the surface of (**a**) DETA-OSER, before being soaked in HMDS. (**b**) DETA-OSER, after being soaked in HMDS.