Droplet Impact and Wetting on a Micropillared Surface

Droplet impact and wetting on non-wetting micro-textured surfaces have applications in manufacturing innovative heat-transfer devices. Inspired by examples in nature, we examine the interaction of sessile droplets with the micro-pillared surfaces of superhydrophobic nature (contact angle \(\sim\) 150°), with square and hexagonal arrangements of pillars. These physically textured surfaces were fabricated using photo-lithography and are quantitatively characterized by surface height correlations. The solid-area fraction for the two surfaces is kept constant. Experiments show that the contact angles are almost similar on both types of arrangement in the ‘air-pocket’ (Cassie) state in a wide range of solid area fractions, however, a significant difference is observed for the lower values of solid area fraction: in this regime, the contact angles for squared-pillar arrangement exhibits a plummet. The droplet impact revealed that, at low solid-area fraction, hexagonal arrangement continues to show complete bouncing behaviour for higher Weber number while in square arrangement droplet transits to Wenzel-state at significantly lower Weber number.