Relationship between hydrophobicity and drag reduction of SiO2/HLR-Si coatings

The one-step spraying deposition method using hydrophobic SiO2 and fluorine-silicone resin (HLR-Si) was adopted in this paper to prepare the hydrophobic micro-nanoscale hierarchical structure on the surface of the test sample. Scanning electron microscopy and atomic force microscopy were used to characterize the surface morphology of the coating, and the contact angle meter was employed to evaluate the surface wettability. The content of hydrophobic silica produced on the hydrophobic performance of the coating was studied, and the relationships between hydrophobic performance and drag reduction performance were investigated. Results show that the one-step spraying deposition method is a simple and efficient technique for coating preparation. The maximum contact angle of SiO2/HLR-Si coating is 163, and the sliding angle is only 1.8. Compared with the 96 pure HLR-Si resin coating, the maximum drag reduction rate of the prepared superhydrophobic coating is 23.4%. Furthermore, the water resistance increases with the contact angle when the contact angle is less than 150, while the drag reduction effect is improved with the increase of the contact angle when the contact angle is larger than 150. However, the effect of drag reduction disappears when the rotation speed is excessively high. Finally, results verified that the air film captured by the superhydrophobic surface can reduce the water resis-tance through the method of artificial air supplement.