# Research on Hard, Transparent and Hydrophobic Coating on PMMA Sheet
## 2 Materials and Methods
### Characterizations  
Use a standard contact angle tester (SL-200A, Kono, USA) to measure the wetting angle of the self-cleaning coating, use a UV-VIS-NIR spectrometer (UV3600, Tsushima, Japan) to measure the visible light transmittance of the coating, and use a Fourier transform infrared spectrometer (FTIR, Nicolet6700, Thermophile, USA) to measure the infrared spectrum of the coating. Use a cold field emission scanning electron microscope (SEM, JSM-7500F, Japan Electronics Co., Ltd.) to observe the microstructure of the coating surface, use a hand-pushed pencil hardness tester (QHQ-A, Zhejiang Aipu) to measure the hardness of the coating according to ISO 15184:2020 Paints and Varnishes-Determination of Film Hardness by pencil test, and use a Baige knife (QFH-A, Zhejiang Airupu) to measure the adhesion of the coating according to ISO 2409:2020 Paints and Varnishes-Cross-Cut Test. The judgment standards of coating adhesion are shown in Table 1.  
The water-flow scouring resistance of the prepared coating was evaluated through a laboratory self-made test device as shown in Figure 1, where the rotor stirred the deionized water to form an annular flow. The coating sample was fixed at the same height level as the rotor blades, and the coating surface was perpendicular to the radial direction. The rotor radius R was 40 mm, and the distance d from the coating surface to the axis was 50 mm. The rotor speed was 2000 rad/min. The wettability and transparency after 20 h and 40 h scouring were detected.  
The microorganism attachment behavior of the prepared coating was evaluated by a microbial immersion test. Specifically, immerse the sample in sterilized seawater for 12 h, and then take it out and immerse it in the phaeodactylum tricornutum solution with a concentration of 2 \(\times\) 10\({}^{6}\) for 6 h. After the immersion test, the sample surface is washed with ultrapure water for 30 s. The microorganism attachment rate is calculated by counting the adhesion area rate with a fluorescence microscope (FM, ZEISS, Germany). A total of 20 random fields magnified by 40 times were taken by the fluorescence microscope for each sample. The adhesion area was evaluated via an Image processing software (Image pro-plus).  
\begin{table}
\begin{tabular}{c c} \hline
**Classification** & **Description** \\ \hline
0 & The edges of the cuts are completely smooth; none of the squares of the lattice is detached. \\
1 & Detachment of small flakes of the coating at the intersections of the cuts. A cross-cut area not greater than 5\% is affected. \\
2 & The coating has flaked along the edges and/or at the intersections of the cuts. A cross-cut area greater than 5\%, but no greater than 15\%, is affected. \\  & The coating has flaked along the edges of the cuts partly or wholly in large ribbons, and/or it has flaked partly and wholly on different parts of the squares. A cross-cut area greater than 15\%, but not greater than 35\%, is affected. \\  & The coating has flaked along the edges of the cuts in large ribbons and/or some squares have detached partly or wholly. A cross-cut area greater than 35\%, but not greater than 65\%, is affected. \\
4 & squares have detached partly or wholly. A cross-cut area greater than 35\%, but not greater than 65\%, is affected. \\
5 & Any degree of flaking that cannot even be classified by classification 4. \\ \hline \end{tabular}
\end{table}
Table 1: Classification of test results for coating adhesion.  
Figure 1: Schematic diagram of water-flow scouring test.