Hierarchical hydrophobic surfaces with controlled dual transition between rose petal effect and lotus effect via structure tailoring or chemical modification

Abstract The divergences in superwettability between lotus leaves and rose petals result from minute differences in their morphological features. The fabrication of these hierarchical structures with unique wetting behaviors is fascinating but challenging. In this paper, a simple and cost-effective approach for controllable fabrication of hierarchical surfaces is presented. Two kinds of hierarchical polymethyl methacrylate (PMMA) structures, including microhemispherical and micropillar arrays covered with nanowires, were obtained by directly molding from anodic aluminum oxide (AAO) templates using UV lithography and two anodization steps. Multiscale structural features and surface chemical compositions influenced the adhesiveness of water droplets to the surfaces. The surface morphologies were precisely controlled by regulating the anodization condition of the AAO templates. The hierarchical surface with either a microhemispherical or micropillar array exhibits excellent hydrophobicity. Surfaces bearing micropillar arrays with –COOH modification show a rose petal effect but switch to a lotus effect after fluorination of the surface. In contrast, surfaces bearing microhemisphere arrayed hierarchical structures always show a rose petal effect, independent of the chemical composition of the surfaces. The controllable fabrication of surfaces with different wettability behaviors and switching between the lotus and rose petal effect is important for the design and fabrication of surfaces with desired properties.