Preparation of Large-Area Anodic Oxide Films with Regularly Arranged Pores by Two-Step Anodization of Stainless Steel Substrates and Application to Superhydrophobic and Superoleophobic Surfaces

An anodic oxide film with regularly arranged pores was obtained by two-step anodization of a stainless-steel (SS) substrate in ethylene glycol containing NH4F. The effect of the electrolyte composition on the pore arrangement was investigated to prepare large-area anodic oxide films with regularly arranged pores. It was found that the concentrations of H2O and NH4F in the electrolyte significantly affected the pore arrangement. It was also confirmed that the degradation of the electrolytes affected the pore arrangement. To form a large-area anodic oxide film with regularly arranged pores, it is essential to use a sufficient amount of an electrolyte with an appropriate composition to minimize the effect of electrolyte degradation. An ordered anodic oxide film with a size of 50 mm x 50 mm was obtained using two-step anodization of the SS substrate under optimized conditions. It was also shown that a surface with hierarchical nanomicrostructures could be fabricated when two-step anodization was performed on an SS substrate with microstructures. When the obtained sample was treated with fluoroalkyl silane, it acted as a superhydrophobic and superoleophobic surface. Large-area anodic oxide films with regularly arranged pores can be utilized in various applications, including capacitors, water-splitting devices, solar cells, and surfaces with highly controlled wettability.