Spontaneous transport of water nanodroplets on graphene and hexagonal boron nitride in-plane heterostructure

Abstract

Developing a surface inducing water droplets to transport spontaneously is very important to energy conversion. Here we demonstrate by the molecular dynamics simulations that a water nanodroplet on graphene and hexagonal boron nitride (h-BN) in-plane heterostructure can move spontaneously from the narrower end of the wedge-shaped h-BN track to the wider end. The driving force comes from the capillary force caused by the surface energy gradient at the edge of the connection, which is attributed to the different interactions of the water nanodroplet with graphene and h-BN. The energy analysis shows that the h-BN acts as a driving force, while graphene as a hindrance. We analyze the forces exerted on the water droplet and propose a theoretical model which indicates that the moving speed of the water nanodroplet can be controlled by the wedge angle and temperature. The present study suggests that the graphene/h-BN heterostructure is a potential material for driving droplets motion and can be explored to find applications in microfluidic systems.