Droplet Transport in Two-Dimensional Channel Driven by Interlayer Distance-Induced Wettability Gradient.

Droplet transport in nanochannels plays a vital role in energy conversion, drug delivery, and nanofluidic applications. Unlike driving approaches relying on an external field, wettability gradient offers a novel strategy for autonomous droplet transport. In this study, a two-dimensional nanochannel with a wettability gradient consisting of a double-layer graphene is constructed, which is utilized to achieve spontaneous and directional droplet transport. The simulation results reveal that the droplet motion within the nanochannel is driven by the wettability gradient between the front and rear surfaces, leading to a two-stage dynamic process characterized by an initial acceleration followed by deceleration. In the small droplet regime, increasing droplet size facilitates transport. Moreover, enhancements in the wettability of the external material or inclination angles within specific ranges promote migration, while increases in channel height or interlayer distance within a certain range exert an inhibitory effect. This work systematically investigates the synergistic coupling of multiple influencing factors through numerical simulations to determine the optimal transport regime. These insights are ultimately leveraged to design wettability gradient surfaces based on two-dimensional materials and offer potential applications in fields such as drug delivery and microfluidics.