Correlation between Hydrophilicity and Surface Aggregation in Anodized TiO2 Nanotube Arrays

Aligned TiO2 nanotube array through anodization method often comes with a surface aggregation layer of TiO2 nanowires. To achieve high photoelectrochemical(PEC) performance, aggregation must be avoided during synthesis or removed via post-processing methods. We present here an efficient method of evaluating the extent of surface aggregation on TiO2 nanotube arrays through water contact angle measurement. Our results indicate that water contact angle on a clean TiO2 nanotube array is almost negligible, with a good correlation between aggregate coverage ratio and contact angles as the aggregation layer increases. This enables a convenient and reliable procedure for quantitatively characterize the surface aggregate level on a macroscopic scale.