Emerging light-responsive functional surfaces for droplet manipulation

Precise manipulation of the droplet is essential in both fundamental research and practical applications, from cargo pick-up to biological diagnostics, thus functional surfaces with specific wettability that are sensitive to external stimuli have aroused broad interests in droplet manipulation on demand. Light, an intriguing stimulus format, provides an ideal platform for remote and contactless droplet manipulation with outstanding temporal and spatial accuracy, which is typically induced by photochemistry, photomechanics, light-induced Marangoni effects and light-induced electric fields. In this Review, emerging progress of light-responsive functional surfaces for droplet manipulation from perspectives of fundamental principles, categories and structural characteristics of the functional surfaces, as well as corresponding prototypical preparation techniques are revisited. In addition, the advanced inspiring applications of light-responsive functional surface in droplet motion are summarized, including manipulation of soft matter and information, harvesting of soft matter and energy, materials manufacturing and multiphase separation, and chemical analysis and bio-related applications. Finally, the frontier challenges and future outlook associated with the light-responsive functional surface for droplet manipulation are prospected, which is critical for the further development of this cross-fertilized research field.