Colloidal Transfer Printing–Mediated Fabrication of Zinc Oxide Nanorods for Self‐Cleaning Applications

Fabrication of superhydrophobic surfaces with extremely low contact angle hysteresis ((CAH) < 4 degrees), which exhibits excellent self-cleaning behavior by colloidal template-guided hydrothermal growth of zinc oxide nanorods (ZnO NRs), is reported. A hexagonal close packed monolayer of polystyrene (PS) colloids is first deposited by spin coating on a thin poly(methyl methacrylate) (PMMA) film. Subsequently, the colloidal array is transferred to a substrate precoated with sputtered zinc oxide seed layer by UV-Ozone (UVO) mediated colloidal transfer printing. ZnO NRs are grown with colloids of different diameter (d(D)) varying between 300 and 800 nm, and for each d(D) the growth time (t(G)) is optimized to obtain maximum level of hydrophobicity. These experiments show that best self-cleaning property is achieved with colloids having d(D) = 600 nm and t(G) = 4 h, which do not require any subsequent low surface energy coating. Using transfer printing allows uniform coverage of the monolayer colloidal array over the sputtered seed layer spanning over large areas, irrespective of the roughness or curvature of the target substrate.