Large-Scale, Uniform, and Superhydrophobic Titania Nanotubes at the Inner Surface of 1000 mm Long Titanium Tubes

Large-scale and mass production of uniform nanostructured materials has been a growing challenge. Anodic titania nanotubes have been widely employed in various applications, which are usually demonstrated with limited size and planar geometry. In this study, a coaxial electrochemical anodization approach is explored and reported. With this method, uniform titania nanotube arrays are produced at the inner surface of titanium tubular electrodes of 1000 mm in length and 10 mm in diameter, in good contrast to the nonuniform nanotubes attained with a conventional anodizing scheme. Such an approach is cost-effective and energy-efficient. It is also capable of processing other valve metals possible for anodization and even longer tubular substrates. The wetting property of the resulting nanotube arrays is further tailored, with a maximum contact angle of 166° for water and 163° for glycerol, exhibiting a superhydrophobic feature. An equation is derived to compute the intrinsic contact angle of a spherical drople...