Numerical simulations of guided self-propelled jumping of droplets on a wettability gradient surface

The direction control of self-propelled jumping of droplets has great significance for efficient chip cooling, anti-icing and self-cleaning. The transport mechanism of guided self-propelled jumping needs to be further explored since it is different in many ways from the extensively-studied vertical jumping of coalescing droplets on surfaces without a surface energy gradient. In this work, the VOF method was used to simulate the guided self-propelled jumping of droplets on superhydrophobic, wettability gradient surfaces. The effects of the surface energy gradient and the initial droplet arrangement on the jumping velocity and energy conversion efficiency are investigated. The results show that the jumping direction is tilted to the side with a smaller contact angle, rather than being perpendicular to the surface, due to the uneven force distribution along the three-phase line. In addition, the surface energy gradient reduces the droplet symmetry resulting in a lower energy conversion efficiency.