Directional self-motion of nanodroplets driven by controlled surface wetting gradients

The self-propelled movement of droplets is essential for numerous applications. To obtain a microscopic insight on the self-propelling dynamics of droplets, droplet movement under different surface wettability gradients needs to be studied. In this study, a method is proposed to control the droplet motion using a continuous surface wettability gradient via molecular dynamics simulation. The effects of single gradient, continuous gradient, and nonlinear complex wetting gradient on the self-propelling dynamics of droplets are investigated. The results show that the droplet motion can be driven in a directional way by carefully designing the wetting gradient surface. On a single wetting gradient surface, the droplet speed increases with the wettability gradient. On a linear continuous wetting gradient surface, the droplet trajectory is consistent with the gradient direction. On a complex wetting gradient surface, the droplet trajectory can be a circle, a sine function curve, or a U-shaped curve. By ingeniously designing the wetting gradient surface, the proposed method for the self-propelled movement of droplets can be extended to more interesting paths. This study presents a microscopic perspective on the directional self-propelled movement of droplets on surfaces with wettability gradient and provides guidance for the application of droplet directional transport.