Diamond turned hierarchically textured surface for inducing water repellency: analytical model and experimental investigations

Abstract Functional surfaces have gained a lot of interest due to enhancement in water repellency for advanced engineering applications. In the present era, single and multi-level texturing is usually carried out on surfaces for inducing complete water repellency. The role of a hierarchical textured surface for enhancing the contact angle (CA), however, has not been extensively studied and understood. In the present work, the physical interpretation of water droplet activity on a hierarchical textured surface has been studied by the development of a mathematical model taking into account different forces responsible for inducing water repellency. Subsequently, hierarchical textured surface i.e., arrays of major pillars with rectangular sub-micron minor pillars over its top surface, were fabricated with high precision by using a diamond turn machining (DTM) process. The fabricated hierarchical textured surfaced was investigated based on the structural dimension and static CA. Also, the effects of variation of spacing between major pillars (p), the ratio of spacing between minor pillars to the minor pillar width ( k = p s w t ) and ratio of minor pillar to major pillar width ( v = w t w ) with CA were studied. The developed mathematical model was able to predict the water CA with dimensions similar to experimentally fabricated hierarchical textured surface with an error of 6.67%. The model is capable of designing and optimizing the hierarchical textured surface of various sizes, which enables their manufacturing in a cost-effective way.