Controllable lubricant-infused wrinkled surface for light-manipulated droplet climbing/pinning on inclined surfaces

Abstract

Stimuli-responsive droplet transport on solid surfaces holds significant importance in various engineering domains; however, achieving accurate and robust manipulation of droplets, particularly their climbing and pinning on inclined surfaces, remains an unresolved challenge. This study proposes a novel light-responsive surface that integrates wrinkle structure with a lubricant-infused photothermal film, enabling flexible light-controlled movement of droplets even on inclined surfaces. The key to constructing this surface lies in fine control of the lubricant infusion amount onto a wrinkled Fe₃O₄/polydimethylsiloxane (PDMS) composite film, where wrinkles were “half covered, half exposed”. Thus, a droplet placed on this controllable lubricant-infused wrinkled surface (CLWS) comes into contact with both the lubricant and the raised parts of wrinkles. In the absence of light, the droplet pins onto the inclined surface, displaying a large sliding angle up to 50°. Upon exposure to external light, the droplet exhibits climbing ability on inclined surfaces with a tilt angle larger than 15°. This behavior is primarily attributed to the Marangoni effect generated by photothermal conversion, which not only provides the driving force for climbing but also alters the distribution of lubricant to mitigate the resistance. The proposed CLWS demonstrates its suitability for various droplets including water, glycol and glycerol, while enabling complex operations such as directional movement, Z-shape turning, and multi-droplet fusion on inclined or curved surfaces. We believe that our proposed CLWS, designed for light-induced droplet climbing/pinning on inclined surfaces, significantly augments the versatility and application potential in the realm of droplet manipulation techniques.