Realization of superhydrophobic aluminum surfaces with novel micro-terrace nano-leaf hierarchical structure

Abstract

Metallic superhydrophobic surfaces are an important class of superhydrophobic materials. We used a simple method to fabricate micro-terrace nano-leaf hierarchical structures to realize superhydrophobicity on commercial aluminum sheets. Microscaled rough surfaces were produced by a simple etching method using Beck’s etchant while nanoscale structures were achieved by dipping in sodium chloride solution. Subsequently, they were fluorinated to decrease the surface free energy. The advantages of hierarchical structures were demonstrated by comparing the superhydrophobic properties in nano-leaf, micro-terrace, and micro-terrace nano-leaf hierarchical structures; the water contact angle increased from to 172° with transition of the surface from a micro-terrace or nano-leaf structure to a micro-terrace nano-leaf hierarchical structure. Sliding angles were extremely low (1°) in both cases. The fabricated aluminum surfaces were stored at very cold and very hot temperatures in air and water; they retained their superhydrophobicity for long times under all conditions, demonstrating the high stability and durability of the fabricated layers under severe conditions. As expected, the hierarchical structure also showed self-cleaning properties. As the approach for producing superhydrophobic aluminum surfaces is very facile and inexpensive, the present method can be easily used to realize superhydrophobic surfaces on other metals and alloys.