Boosting\nDroplet Transport for Fog Harvest

Wedge-shaped\nsuperhydrophilic tracks have been considered as one\nof the most effective ways to transport droplets for diverse cutting-edge\napplications, e.g., energy harvesting and lab-on-a-chip devices.\nAlthough significant progress, such as serial wedge-shaped tracks\nwith curved edges, has evolved to advance the liquid transport, the\nultrafast and long-distance transporting of drop-shaped liquid remains\nchallenging. Here, inspired by the cactus spine that enables fast\ndroplet transport and the serial spindle knot of spider silk, which\nis capable of collecting condensate from a wide range of distances,\nwe created serial wedge-shaped superhydrophilic patterns and optimized\ntheir side edges with a convex brachistochrone curve to boost the\nacceleration. The junctions of the serial patterns were meanwhile\nreformed into concave brachistochrone curves to lower the energy barrier\nfor sustained transport. For transporting the liquid in drop shapes\nto the long distance at high velocity, the wedge-shaped tracks were\nslenderized to the greatest extent to suppress the liquid spreading\nand thus prevent the degradation of the Laplace driving force. Moreover,\nthe junction that determines the energy barrier of droplet striding\n was carefully designed based on the principle of minimizing momentum\nloss. The exquisite architecture design pushed the droplet transport\nto a maximum instantaneous velocity of 207.7 mm·s<sup>–1</sup> and an outermost transport distance of 120.5 mm, exceeding most\nwettability or geometric gradient based reports. The transported volume\nof the droplets can be readily regulated by simply scaling the created\narchitectures. The enhanced droplet transport facilitates the motion\nand departure of the cohered droplets, enabling a 1.9-fold rise of\nthe water collection rate and 12-fold increase of the heat transfer\ncoefficient during the fog harvest test. This scalable, controllable,\nand easily fabricatable surface design provides an essential pathway\nin realizing high-performance manipulation of droplets and possibly\npioneers substantial innovative applications in multidisciplinary\nfields. Those include but are not limited to energy harvesting, lab-on-a-chip\ndevices, and MEMS systems.