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.
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