Ultrafast self-propelled water droplet transport on a graphene-covered nanocone

Abstract

Cacti, a common drought-tolerant plant, enable the directional transport of droplets from the tip of the spikes to the roots in order to collect moisture from the air, creating conditions for cactus survival in arid areas. Inspired by this interesting natural phenomenon, a novel design for a monolayer graphene-covered nanocone (GNC) is proposed to realize ultrafast water droplet transport from the tip to the end of the GNC. The results show that the self-driving speed of a water droplet can reach ∼80 m s−1 driven by the Young–Laplace pressure difference. The rule of energy change during the droplet self-driving process indicates that the potential energy of the droplet and the interaction energy between the droplet and the GNC undergo cooperation and competition successively, resulting in the droplet first speeding up and then slowing down to a steady moving state. A larger droplet can extend the high-speed stage, which is beneficial to long-distance self-driving of droplets in a water-harvesting process. Continuum theory in the self-driving of a droplet at a microscale is used to describe the steady moving process, in order to further understand the rule in GNC-based water transport. The findings will open a broad range of novel perspectives for spontaneous droplet transport and water harvesting by graphene-covered functional surfaces.