关键词: 木材表面, 等离子体刻蚀, 等离子体化学气相沉积, 碳氟薄膜, 超疏水

Abstract: [Objective] The greatest disadvantage of wood in actual applications is its hygroscopicity, hydroxyl groups on the porous surface readily form hydrogen bonds with adsorted water molecules. In order to inhibit or reduce moisture adsorption on the surface of wood, this study fabricated superhydrophobic wood surfaces, therefore, prolong the lifetime of wood and improve its service performance, and provide a method for creation of superhydrophobic wood using plasma technology.[Method] Firstly,the radial sections of Acer saccharum Marsh. wood were etched for different times with an O₂ plasma at a discharge power of 150 W and working pressure of 66 Pa. The effect of O₂ plasma etching time on morphology and roughness of wood surfaces was investigated using scanning electron microscopy (SEM) and laser scanning confocal microscope (LSCM) profilometry. Then, the superhydrophobic wood were fabricated by plasma chemical vapor deposition of fluorocarbon film which has lower surface free energy on etched wood surfaces from a mixture of pentafluoroethane (PFE) and argon gas at a discharge power of 120 W and working pressure of 133 Pa. The wetting behavior of the treated wood was determined by static water contact angle and roll-off angle measurement. Furthermore, the morphology, thickness of deposited films, element composition and their chemical bonding information of wood surfaces before and after deposition treatment were also measured and analyzed by SEM, ellipsometer and X-ray photoelectron spectroscopy (XPS).[Result] The average roughness (S_a), root mean square roughness (S_q) and peak-to-valley roughness (S_z) of wood surfaces increased with the etching time within 30 min. However, the wood surface roughness decreased slightly after prolonged etching time to 45 min. when the time of deposition fluorocarbon film was fixed at 40 s, the static water contact angles did not change significantly as a function of etching time, but the roll-off angles of wood surfaces decreased gradually with increasing etching time, moreover, the roll-off angles along the grain direction were always smaller than those across the grain direction. The static water contact angles of wood surfaces without prior O₂ plasma etching displayed a gradually decreasing trend with the increasing of deposition time, and water drops always remained "pinned" to the wood surface even when the substrate was tilted to 90°. Ellipsometer results showed that the thickness of deposited films exhibited a linear increase trend with the increasing of deposition time. When the etching time was 15 min or 45 min, the static water contact angles did not change significantly as a function of deposition time, but the roll-off angles of wood surfaces reduced firstly and then increased with the increasing time for fluorocarbon film deposition. It should be noted that the static water contact angle of the sample treated by 45 min etching and deposition of fluorocarbon film for 40 s was as high as 160.6°±0.4° and showed the lowest roll-off angle of 11.5°±1.2°(along grain) and 14.7°±2.5°(across grain). XPS analysis showed that almost 50% fluorine atoms were found on the wood surfaces deposited with fluorocarbon film and the C1s spectra exhibited that the surface composition of fluorocarbon film was heterogeneous with-C-CFx, -CF₃, -CF₂, and -CF groups indicating that this film was highly cross-linked.[Conclusion] This study demonstrated the probability to fabricate superhydrophobic wood surfaces with O₂ plasma etching prior to fluorocarbon film deposition. The treated wood exhibited superhydrophobicity (the static water contact angle >150°) with low roll-off angles, and could avoid water droplets adhere to wood surface effectively.

Key words: wood surface, plasma etching, plasma chemical vapor deposition, fluorocarbon film, superhydrophobicity