CONTROLLING THE MOVEMENT OF WATER DROPLETS WITH MICRO- AND HIERARCHICAL MICRO/NANOSTRUCTURES

Abstract

Anisotropic surfaces with micropillar- or micropillar/nanobump structures and anisotropic wetting behavior were fabricated. Structures were arranged as three parallel zones where the structure of the middle zone differed from that of the edge zones. The widths of the middle zones were increased systematically, and the effects of the middle zone structures and widths on the contact and sliding angles of water were investigated. Structures were fabricated on PP by injection molding. Microstructured mold inserts for injection molding were obtained by structuring aluminum foils with a microworking robot, and hierarchically structured mold inserts by anodizing the microstructured foils. It was possible to create surfaces where the microstructure in the middle zone was lower or higher than on the edges, or where the middle zone had only nanostructure or was unstructured. The behavior of water on the surfaces was characterized by measuring the dynamic contact angles and sliding angles parallel and perpendicular to the zones. Hydrophobic surfaces were achieved. With appropriate middle zone widths, clearly differing parallel and perpendicular contact angles were measured and elongation of droplets along the middle zones was detected.