Directional rebound of compound droplets on asymmetric self-grown tilted mushroom-like micropillars for anti-bacterial and anti-icing applications

Abstract

Directional liquid bouncing is of great significance for a variety of biological and industrial applications. Although surface engineering through 3D printing or self-assembly enables water droplets to rebound directionally, directional bouncing of compound droplets still poses a challenge due to their low surface tension. Moreover, preparation of superamphiphobic surfaces in an efficient and simple manner to accomplish this mission remains to be studied. Here, a tilted stepped mushroom-like micropillar surface (TSMMs), whose structural morphology can be created and tailored by a facile and direct femtosecond laser-induced asymmetric self-growing strategy, is designed to enable the oblique quasi-pancake bouncing of a low surface tension droplet (γ = 32 mN/m). Oblique quasi-pancake bouncing can not only reduce the droplet contact time (7 ms) but also effectively control the direction of droplet bouncing (the horizontal distance of 2.4 mm). Accompanying mechanistic analysis provides an in-depth understanding of the structure-droplet motion relationship. Finally, we demonstrate the applications of TSMMs in antibacterial and anti-icing scenarios. This work advances the investigation of directed droplet transportation, and paves new avenues in the fields of advanced biomedical and other industrial materials.