Tailoring the wettability of TiO2 nanotube layers

Self-organized TiO2 nanotube layers were grown on Ti by electrochemical anodization. As prepared, these layers showed a super-hydrophilic wetting behaviour. When modified with organic molecules, octadecylsilane (C18H37SiH3) or octadecylphosphonic acid (C18H37PO(OH)2), the layers show a super-hydrophobic behaviour. We demonstrate how the tubular geometry of the TiO2 layers combined with UV induced decomposition of the organic monolayers (SAM) can be used to adjust the surface wetting properties to any desired degree from super-hydrophobic to super-hydrophilic.