Sculpting Tiered Micro-Nanogradient Structure by Anisotropic Stepped Anodization for Mediating Water Distribution and Transportation

Tiered micro-nanogradient structures with custom-tailored profiles and dimensions can be fabricated by the anisotropic electrochemical anodization of aluminum, where the micro and nanostructures are simultaneously formed. The microgradient structures can be sculpted by the chronological and spatial order of polymer masking followed by step anodization; the nanostructures can be controlled by electrochemical conditions in step anodization. Water spatial distribution and directional transportation abilities of the exemplified micro-nanogradient structures (i.e., tiered micro symmetric circular structure, microasymmetric circular structure, and microrectangular step structure which are all integrated with nanotip-capped nanopore structure) are studied under the fogging condition. It is found that despite the directional self-jumping of the microdroplets caused by the cooperation of asymmetric structure and wind blowing, microdroplets can also be quickly gathered on the topper tier of the gradient structures to form large droplets and then roll away along the descending direction of the structures (also wind blowing direction), which sweep the microdroplets they passed by. These tiered micro-nanogradient structures not only have potentials to become high efficiency fog collector but also could be a platform for the preparation of tiered micro-nanogradient structures of various materials with advanced functions.