Liquid Confine-Induced Gradient-Janus Wires for Droplet Self-Propelling Performances in High Efficiency

Constructing surface wetting gradients usually involves complex physical or chemical methods. Here, a novel Gradient-Janus wire (GJW) can be designed based on the theory of newly Liquid Confined Modification (LCM). In LCM theory, reaction difference will be generated by the confinement of reaction solution, which constructs wettability discrepancy on the same curve surface. Thus a unique continuous Gradient-Janus wetting region can be constructed in a long range on a 1D wire. It is demonstrated that GJW can propel water droplets to transport the distance of ≈73 mm in 0.9 s, and liquid bridge to 85 mm (the longest among this kind of study) in 0.79 s with peak velocity high up to 237 mm s⁻¹ (over 20 times faster than droplet transport on surface of Sarracenia trichome). The mechanism is attributed to cooperation between imbalanced Laplace pressure and surface tension force to generate the driving force act on droplet, liquid bridge, or column transport, respectively. LCM directs the large-scale facile fabrication of GJWs within 20 s. A large-scale GJW array can achieve the high-efficient transport of water droplet in a wide volume range (few µL to 1 mL), making it potential in fogwater harvesting.