UV-regulated wettability and directional droplet self-transport on SnO2 triangular patterned surfaces

The directional self-transport of water droplets holds significant application value in fields such as microfluidics and water collection. Current research mostly focuses on single wettability gradients or fixed surface structures, lacking systematic exploration of dynamic wettability regulation and SnO 2 -based intelligent surfaces. In this study, a triangular-patterned SnO 2 surface (TPSS) was constructed via anodic oxidation combined with ultraviolet (UV) irradiation. Dynamic regulation of surface wettability was achieved by adjusting the UV irradiation time, and the influence of wettability changes on the self-transport behavior of water droplets was systematically investigated. The results showed that no directional self-transport of water droplets occurred when the water contact angle (WCA) was greater than 33°; water droplets transported directionally in a droplet-like form when the WCA ranged from 10° to 33°; when the WCA was less than 10°, water droplets spread into a film-like form with a significant decrease in transport speed, but the addition of a second water droplet could recondense them and restore their self-transport capability. Combined with X-ray photoelectron spectroscopy (XPS) characterization and in-situ optical observation, the synergistic regulation mechanism of Laplace pressure difference and hysteresis force was clarified. Moderate UV irradiation enhances surface hydrophilicity, and the Laplace force generated by the curvature difference overcomes the hysteresis resistance to drive the droplet transport. Excessive UV irradiation, causing the water droplets to spread and the Laplace force to attenuate, while the liquid film can restore the droplet-like form and transport capability through a buffering effect. This study provides an experimental basis and theoretical support for the design of dynamically adjustable microscale water droplet self-transport intelligent surfaces, expands the application of SnO 2 in fields such as microfluidics and micro-detection, and realizes an efficient fog collection function based on TPSS.