Durable Lubricant-Infused Surfaces with Hierarchical Structures of Submicrometric Reservoirs and Metal-Oxide Nanograss

Lubricant-infused surfaces (LISs) offer exceptional slippery and nonwetting properties by utilizing a liquid-liquid interface with a lubricant layer trapped in rough surface structures. The performance of LISs relies on maintaining a durable layer of lubricant on the surface, and hierarchical surfaces composed of micrometer-scale voids and nanometer-scale rough structures were generally expected as a solution to enhance lubricant storage and distribution. However, the previous hierarchical surfaces mainly failed to achieve the expected performance of lubricant retention due to the significant size discrepancy between the dimensions of the micrometric substrate patterns and the additive nanostructures. In this work, we present a refined design for hierarchical nanoporous surfaces, featuring similarly scaled submicrometric reservoirs (similar to 300 nm) and nanometric grass-like structures, to enhance the retention and redistribution of the infused lubricant. The reservoirs are fabricated using self-assembled patterns of anodic aluminum oxide (AAO) and the grass-like nanostructures are formed by chemical oxidation of copper, thus showing facile fabrication steps without complex nanofabrication techniques. The hierarchical surface exhibits up to a 300% increase in lubricant retention performance under droplet shearing drainage conditions compared to reference samples and additionally demonstrates passive refilling of the lubricant layer in previously drained regions. Furthermore, the structural integrity of the surface structures and stable retention of the infused lubricant are confirmed under high inertial forces and repeated experiments. The increased lubricant retention performance and structural durability demonstrated by the fabricated surface offer promising alternatives for developing LIS with enhanced durability and functionality.