title: Effect of annealing temperature on wettability of TiO2 nanotube array films.
abstract: Highly ordered TiO2 nanotube array (TN) films were prepared by anodization of titanium foil in a mixed electrolyte solution of glycerin and NH4F and then annealed at 200°C, 400°C, 600°C, and 800°C, respectively. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), water contact angle (WCA), and photoluminescence (PL). It was found that low temperature (below 600°C) has no significant influence on surface morphology, but the diameter of the nanotube increases from 40 to 50 nm with increasing temperature. At 800°C, the nanotube arrays are completely destroyed and only dense rutile film is observed. Samples unannealed and annealed at 200°C are amorphous. At 400°C, anatase phase appears. At 600°C, rutile phase appears. At 800°C, anatase phase changes into rutile phase completely. The wettability of the TN films shows that the WCAs for all samples freshly annealed at different temperatures are about 0°. After the annealed samples have been stored in air for 1 month, the WCAs increase to 130°, 133°, 135°, 141°, and 77°, respectively. Upon ultraviolet (UV) irradiation, they exhibit a significant transition from hydrophobicity to hydrophilicity. Especially, samples unannealed and annealed at 400°C show high photoinduced hydrophilicity.
authors.affiliation: School of Physics and Materials Science, Anhui University, Hefei 230601, People's Republic of China ; New Star Institute of Applied Technology, Hefei 230031, People's Republic of China.
authors.forename: Lei
authors.initials: L
authors.lastname: Yang
authors.affiliation: School of Physics and Materials Science, Anhui University, Hefei 230601, People's Republic of China.
authors.forename: Miao
authors.initials: M
authors.lastname: Zhang
authors.affiliation: School of Physics and Materials Science, Anhui University, Hefei 230601, People's Republic of China.
authors.forename: Shiwei
authors.initials: S
authors.lastname: Shi
authors.affiliation: Department of Physics and Electronic Engineering, Hefei Normal University, Hefei 230061, People's Republic of China.
authors.forename: Jianguo
authors.initials: J
authors.lastname: Lv
authors.affiliation: School of Physics and Materials Science, Anhui University, Hefei 230601, People's Republic of China.
authors.forename: Xueping
authors.initials: X
authors.lastname: Song
authors.affiliation: School of Physics and Materials Science, Anhui University, Hefei 230601, People's Republic of China.
authors.forename: Gang
authors.initials: G
authors.lastname: He
authors.affiliation: School of Physics and Materials Science, Anhui University, Hefei 230601, People's Republic of China.
authors.forename: Zhaoqi
authors.initials: Z
authors.lastname: Sun
keywords: Annealing temperature; Photoinduced hydrophilicity; TiO2 nanotube arrays; Wettability