Comprehensively durable superhydrophobic metallic hierarchical surfaces via tunable micro-cone design to protect functional nanostructures

Abstract

Superhydrophobic surfaces have been intensively investigated in recent years. However, their durability remains a major challenge before superhydrophobic surfaces can be employed in practice. Although various works have focused on overcoming this bottleneck, no single surface has ever been able to achieve the comprehensive durability (including tangential abrasion durability, dynamic impact durability and adhesive durability) required by stringent industrial requirements. Within the hierarchical structures developed for superhydrophobicity in typical plants or animals by natural evolution, microstructures usually provide mechanical stability, strength and flexibility to protect functional nanostructures to enable high durability. However, this mechanism for achieving high durability is rarely studied or reported. We employed an ultrafast laser to fabricate micro/nanohierarchical structures on metal surfaces with tunable micro-cones and produced abundant nanostructures. We then systematically investigated their comprehensive mechanical durability by fully utilizing the protective effect of the microstructures on the functional nanostructures via the tunable design of micro-cones. We confirm that the height and spatial period of the microstructures were crucial for the tangential abrasion durability and dynamic impact durability, respectively. We finally fabricated optimized superhydrophobic tungsten hierarchical surfaces, which could withstand 70 abrasion cycles, 28 min of solid particle impact or 500 tape peeling cycles to retain contact angles of greater than 150° and sliding angles of less than 20°, which demonstrated exceptional comprehensive durability. The comprehensive durability, in particular the dynamic impact durability and adhesive durability, are among the best published results. This research clarifies the mechanism whereby the microstructures effectively protected the functional nanostructures to achieve high durability of the superhydrophobic surfaces and is promising for improving the durability of superhydrophobic surfaces and thus for practical applications.