Optimal condition for preparing TiO2 superhydrophobic surfaces on titanium substrate in NH4F/H3PO4 electrolyte by anodization and its self-cleaning effect and anti-icing ability

Abstract Superhydrophobic surface materials on metallic substrate have attracted widespread research interest due to tremendous promising application value in various fields. Superhydrophobic surface on Ti substrate was successfully obtained with a two-step method. Firstly, micro/nano-cone or flower-like structures were fabricated in the mixture solution of H3PO4/NH4F by a simple, cost-effective anodization method, and then modified with stearic acid. The synergistic effect both of them achieved a superhydrophobic surface. Effects of anodization parameters including NH4F concentration in the mixture of H3PO4/NH4F electrolyte, anodization time and anodization voltage on the morphology and wettability of the superhydrophobic surfaces were systematically studied and optimized. It is found that the surface was getting rougher and rougher with the increase of NH4F concentration in the mixture, anodization time and anodization voltage, respectively, meanwhile, the corresponding contact angles (CAs) were gradually increase and corresponding sliding angles (SAs) were gradually decrease, respectively. Results showed that the best superhydrophobicity surface with a maximum CA of ~170.3° and a SA of approximately 0° were obtained at room temperature when the anodizing voltage, anodizing time and the mixture electrolyte concentration were 100 V, 60 min and 5 wt% H3PO4/0.5 wt%NH4F, respectively. Formation mechanisms of the micro/nano-protrusion hierarchical structures were also discussed. Additionally, the superhydrophobic surface exhibited ultralow adhesion, a long-term stability, excellent self-cleaning effect and good anti-icing property.