Oriented bouncing of droplets with a small Weber number on inclined one-dimensional nanoforests.

Asymmetric superhydrophobic structures with anisotropic wettability can achieve directional bouncing of droplets and thus can have applications in directional self-cleaning, liquid transportation, and heat transfer. To achieve convenient large-scale preparation of asymmetric superhydrophobic surfaces, inclined nanoforests are prepared in this work using a technique of competitive ablation polymerization, which allows the control of the inclined angles, diameters, and heights of the nanostructures. In this study, such asymmetric structures with the smallest dimension (230 nm diameter) known are achieved by a simple etching method to guide droplet unidirectional bouncing. With such nanoforests, the mechanism of droplet bouncing on their surface is investigated, and controllable droplet bouncing over a long distance is achieved using droplets with a low Weber number. The proposed structure has a promising future in directional self-cleaning, liquid transportation and heat transfer.