Al ₂O ₃-nanodiamond composite coatings with high durability and hydrophobicity prepared by aerosol deposition

We attempted the room-temperature fabrication of Al ₂O ₃-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al ₂O ₃ powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al ₂O ₃ to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al ₂O ₃ powder by ball milling to ratios of 0.01wt.%, 0.03wt.%, and 0.05wt.% ND. The water contact angle (CA) of the Al ₂O ₃-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al ₂O ₃-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al ₂O ₃-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0wt.% ND. In addition, the Al ₂O ₃-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates.