Photo-controlled water gathering on bio-inspired fibers

We report photo-controlled water gathering on bio-inspired fibers. We have designed a bio-inspired fiber using azobenzene (Azo) polymer materials, with roughness and a curvature similar to the spindle-knots of wetted spider silk. We demonstrate that the cooperation between roughness and curvature and the photo-responsive wettability play a key role in water gathering after Vis or UV irradiation, which regulate effectively the separation of water droplets away from the spindle-knots or the coalescence towards the spindle-knots, respectively. This study offers an insight into the design of novel gradient surfaces that may drive tiny droplets to move in as-desired directions, which could potentially be extended to the realms of fluid-control in micro-scale engines, sub-micron masks, heat transfer, water-collecting devices and systems.