Bidirectional Transport of Split Droplets

Abstract

Simple and smart directional transport of impacting droplets is of great significance for future life and industry, but there are still many challenges due to complex hydrodynamics. Inspired by Setaria viridis leaves, we propose an efficient strategy to manipulate the split and transport of impacting droplets based on the simple design of liquid-repellent surfaces decorated with a ridge, and we report the large-scale, high-speed, and fast-response bidirectional transport of split droplets. Upon impacting on a wirelike ridge, the droplet splits into two parts, which have considerable horizontal transport velocity up to 34% of the initial impact velocity. The transport distance can exceed 1 order of magnitude longer than the droplet size and the response time is reduced by 50% compared to the contact time on flat surfaces. The splitting of the impacting droplet is the precondition for this bidirectional movement, and the time required for splitting strongly correlates to the horizontal transport velocity. A model is developed to accurately predict the splitting time, and a scaling law is proposed to illustrate the quantitative relationship between the horizontal transport velocity and impact parameters. These findings provide a route for using macrostructures to achieve precise droplet manipulation for diverse applications, such as anti-icing and chemical detection.