Facile Fabrication of Super-Hydrophobic Nano-Needle Arrays via Breath Figures Method

Super-hydrophobic surfaces which have been fabricated by various methods such as photolithography, chemicaltreatment, self-assembly, and imprinting have gained enormous attention in recent years. Especially 2D arrays ofnano-needles have been shown to have super-hydrophobicity due to their sharp surface roughness. These arrayscan be easily generated by removing the top portion of the honeycomb films prepared by the breath figuresmethod. The hydrophilic block of an amphiphilic polymer helps in the fabrication of the nano-needle arraysthrough the production of well-ordered honeycomb films and good adhesion of the film to a substrate.Anisotropic patterns with water wettability difference can be useful for patterning cells and other materials usingtheir selective growth on the hydrophilic part of the pattern. However, there has not been a simple way togenerate patterns with highly different wettability. Mechanical stamping of the nano-needle array with apolyurethane stamp might be the simplest way to fabricate patterns with wettability difference. In this study,super-hydrophobic nano-needle arrays were simply fabricated by removing the top portion of the honeycombfilms. The maximum water contact angle obtained with the nano-needle array was 150°. By controlling the poresize and the density of the honeycomb films, the height, width, and density of nano-needle arrays weredetermined. Anisotropic patterns with different wettability were fabricated by simply pressing the nano-needlearray at ambient temperature with polyurethane stamps which were flexible but tough. Mechanical stamping ofnano-needle arrays with micron patterns produced hierarchical super-hydrophobic structures.