Elliptical Superhydrophilic Microregions: A Strategy for Enhanced Spontaneous Droplet Aggregation and Fog Collection

The development of high-efficiency fog collection technology is crucial for alleviating freshwater scarcity. Inspired by the efficient water-harvesting mechanisms of organisms such as the Namib Desert beetle and cacti, this study fabricates a biphilic surface on aluminum (Al), comprising elliptical superhydrophilic (SHL) microregions patterned within a superhydrophobic (SHB) background. The elliptical morphology of SHL microregions can be controlled by adjusting both the defocus distance of the cylindrical lens and the pulse width in a femtosecond laser system. Importantly, these microregions facilitated droplet formation and growth at their centers, regardless of orientation, due to the dominant influence of Laplace pressure gradients. In contrast, rectangular microregions exhibited no such capability. The biphilic surface exhibited significant improvements in fog collection efficiency, outperforming traditional SHB surfaces by factors of 14.2, 5.0, and 3.8 in environments with 70%, 85%, and 95% relative humidity, respectively. Furthermore, the surface patterned with elliptical microregions exhibited a marked advantage in fog collection performance compared to surfaces with rectangular microregions of equivalent area. By optimizing geometrically gradient micropatterns, this study highlights the critical role of edge morphology in controlling droplet self-transport, offering an innovative surface solution for efficient fog collection and expanding the application prospects of bioinspired fog-harvesting technologies.