Hydrophobicity of curved microstructured surfaces

This paper presents measurements and models for how the macroscopic curvature of microstructured polymers affects hydrophobicity. Flexible polymer substrates were fabricated with arrays of regular microstructures. The interaction of liquid drops with these surfaces was analyzed for flat substrates and substrates flexed into either positive or negative cylindrical shapes. Liquid droplet static contact angle and dynamic slide angle were measured for a range of surfaces. An increase in substrate curvature corresponded with decreased slide angle for liquid droplets suspended on the surface asperities. This phenomenon is investigated in terms of solid-liquid contact line and the periodicity of surface microstructures. We present a model that can be used to understand the observed phenomena and to design microstructure geometries for hydrophobicity.