Evolution of nanoliter size fluid droplet on micropatterned surface

Abstract

Static shape of liquid droplets on textured surface draws significant attention from the standpoint of several engineering applications, ranging from heat transfer to bio-printing. This paper discusses the equilibrium behavior of a nanoliter size droplet dispensed on a micropatterned surface. For a given combination of intrinsic wettability of the surface, liquid surface tension and the geometric morphology of the textured surface, the liquid droplet prefers to be on Cassie-Baxter, Wenzel or an intermediate, hybrid state. Here we have carried out an energy-based simulation of nanoliter size droplets on micropatterned surface, using an open-source surface evolver fluid interface tool SE-FIT. A simplified periodic geometry of rectangular (straight or tapered) micro-pillars of specified dimensions is chosen for the micropatterned surface. For a given solid surface texture, we found that droplet prefers to transit from Wenzel to Cassie state beyond a threshold intrinsic sessile contact angle (which the liquid would have subtended on a microscopically smooth surface of the same solid material). This critical transition contact angle is plotted against the roughness parameter. Present study helps in designing the wettability-engineered surfaces for specific engineering applications.