Efficient Autonomous Dew Water Harvesting by Laser Micropatterning: Superhydrophilic and High Emissivity Robust Grooved Metallic Surfaces Enabling Filmwise Condensation and Radiative Cooling

Abstract

The present work explores a unique yet unexplored synergy between the properties of laser micropatterned metallic surfaces and the requirements for an autonomous dew water harvesting candidate material. Laser-patterned aluminum surfaces achieved simultaneously high infrared emissivity (up to 0.95 in the atmospheric window) and superhydrophilic wettability (water contact angle of 0°), key properties enabling passive radiative cooling and filmwise condensation dynamics respectively. The generation of micrometric-sized grooves during laser processing plays a fundamental role in both properties, as they provide a broadband enhancement of the emissivity based on multiscale topographies and oxide layers, while limiting the growth of the water film during condensation through strong capillary wicking forces. As a result, the patterned aluminum surfaces display self-cooling capacities under radiative deficit conditions as well as low water retention levels (three times lower than the untreated dropwise condensation counterparts). The promising results obtained lead to the construction and evaluation of a real size outdoors autonomous dew water harvesting system based on those surfaces, demonstrating the scalability of the technology. A 70% improvement in the collected dew water in comparison to a state-of-the-art reference material is consistently measured during 1-year outdoor study, proving the robustness of the surfaces and their performance.