A novel method to fabricate organic-free superhydrophobic surface on titanium substrates by removal of surface hydroxyl groups

Titanium (Ti) and its alloys have been extensively used for biomedical applications and surface wettability makes large differences during their applications. Especially, superhydrophobic surfaces with water contact angle (WCA) > 150 degrees are under great interest and are now finding increased use in the biomedical arena. Up to now, most fabrication of superhydrophobic surface on Ti substrates would introduce external organics with low surface free energy (SFE), which could influence the intrinsic chemical components of Ti surface and face the risk of degradation when exposed for a long time. But it seems quite difficult to achieve superhydrophobic surfaces on Ti substrates without organic coating and few researches have been reported. Herein, a superhydrophobic Ti surface (WCA = 151.9 degrees) was successfully fabricated by a novel method including anodization, H2O2 and aging treatment. During this procedure, no external organics with low SFE were introduced. Then surface topography and roughness, 3D morphology, wettability, crystalline structure and chemical components of the as-prepared samples were characterized. The as-prepared surface was coated with a TiO2 layer, and exhibited a porous morphology with numbers of crater structures with roughness value (Ra) about 1.21 mu m. It was found the absorption of hydrocarbon and decrease of hydroxyl (OH) groups together changed the intrinsic wettability of Ti surface, where the removal of OH groups by H2O2 and aging treatment played a critical role. The results indicated that surface micro-roughness and declined intrinsic wettability were responsible for the formation of superhydrophobicity. This novel method could achieve superhydrophobicity without changing the intrinsic properties of Ti/TiO2 surface and would have great potential in biomedical applications.