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 × 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.