Three-Level Biomimetic Rice-Leaf Surfaces with Controllable Anisotropic Sliding

Rice leaves with anisotropic sliding properties have the ability to directionally control the movement of water microdroplets. However, the realization of artificial anisotropic sliding biosurfaces has remained challenging. It is found, by a systematic investigation, that the height of 200-mu m-width groove arrays on rice leaves reaches up to 45 mu m, far greater than the smaller microgrooves that are widely adopted for the study of anisotropic wetting. A new model based on three-level microstructures (macro/micro/nano) is developed to interpret the anisotropic sliding behavior. Moreover, artificial rice leaves with different macrogrooves are demonstrated by combining micro/nanostructures and macrogrooves, which are prepared by photolithography, PDMS imprinting, and micro/nanostructure coating. Sliding-angle measurement further prove that the third-level macrogroove arrays are the determining factor for anisotropic sliding. Finally, a new testing method, curvature-assisted droplet oscillation (CADO), is developed to quantitatively reveal the anisotropic dynamic behavior of biomimetic rice-leaf-like surfaces.