Surface wettability of TiO2 nanotube arrays prepared by electrochemical anodization

This work reports structural engineering and wettability of titania nanotube arrays (TNTs). The nanotube diameter and thickness of TNT layer increase with increasing of applied voltage from 20 to 40,60 and 80 V, and the diameter has no relevance to extending anodic duration. The fabricated TNTs are 30-190 nm inner diameter and 5-40 mm height. 10 mL water droplets are applied to define wettability of the TNTs by measuring contact angles. Hydrophilicity is enhanced with increasing diameter of TNTs as well as over etching occurring on the surface. Large diameter tubes and capillary force provide more space and power for liquid to penetration. The contact angle reduces from 35 to 2 with the tube diameter increasing from 30 to 190 nm. Bare Ti foil is inherently hydrophobic with approximately 90 contact angle. The as prepared TNTs are hydrophilic with contact angle of 24, and annealing further improves this property to a contact angle of 13. The bottom of TNTs shows superhydrophilic due to hydroxide compounds existed on the surface. The metal substrate with tube footprint left presents hydrophobic with contact angle of 68, which is lower than the bare one. It is believed that wettability on the surface of TNTs is dependent on their morphology and chemical composition. (C) 2016 Elsevier B.V. All rights reserved.