Fluorine-Induced Superhydrophilic TiO₂ Nanotube Arrays

Continuous water film formed on a hydrophilic or superhydrophilic surface can delay the formation of a vapor film in boiling and thus improve critical heat flux (CHF), therefore, the fabrication of hydrophilic or superhydrophilic surface is an efficient approach to enhance boiling heat transfer. In the present work, superhydrophilic TiO₂ nanotube arrays (TiNAs) interfaces are fabricated by anodization in fluoride contained electrolyte, and the fluorine is found out to be the key factor affecting the wettability of TiNAs interfaces. After anodization, a stable oxy-fluoride layer was formed at the interface as form of -O-Ti-F, the fluorine atoms are linked to the interface as terminal groups. Due to the strong polarity of titanium oxy-fluorides, superhrophilic TiO₂ nanotube arrays interface is obtained. Furthermore, we characterize the stability of titanium oxy-fluorides by storing. After store for 2 months, the inner titanium fluorides (TiF₄) are lost due to its strong volatility. Fortunately, the content of titanium oxy-fluorides remains the same, and retain its remarkable superhydrophilic properties. It is potential to design energy-efficient devices ranging from boiling heat transfer to self-cleaning.