Dual-gradient wettability-patterned surface for droplet rectification and targeted transport

Abstract

Droplet self-transport holds significant implications for applications such as water harvesting, microreactors, and microfluidic chips. Achieving precise and efficient droplet self-transport is therefore crucial. Herein, a dual-gradient wettability-patterned surface (DWPS) incorporating both wettability and structural gradients is proposed, where the wettability gradient facilitates ultrafast droplet transport, while the structural gradient serves to rectify the transport direction, collectively achieving directional droplet rectification and ultrafast targeted self-transport. The influence mechanism of energy conversion on droplet self-transport behavior during oscillatory motion is elucidated. The oscillatory behavior during droplet self-transport can be effectively suppressed through a droplet coalescence strategy. Compared to the single wettability or structural gradient surfaces, the structural gradient surface exhibits the lowest transport efficiency. Although the droplet self-transport efficiency on the DWPS is also lower than that on the wettability gradient surface, it enables precise droplet transport. The mechanisms underlying the self-transport behavior and efficiency variations on the three model surfaces are revealed through an analysis of the relationship between solid-liquid interfacial energy and droplet potential energy. These findings provide a theoretical foundation for the design of functional surfaces aimed at achieving precise droplet self-transport.