Fabrication of artificial Lotus leaves and significance of hierarchical structure for superhydrophobicity and low adhesion

TLDR

Lotus leaves are superhydrophobic and self‑cleaning, and have served as a model for artificial biomimetic surfaces. The study recreates Lotus leaf hierarchical structures to examine how roughness at multiple scales affects superhydrophobicity and adhesion, using flat, microstructured, and nanostructured replicas. Hierarchical surfaces were fabricated by molding the Lotus leaf microstructure and self‑assembling natural wax into nanoscopic tubules via thermal evaporation and solvent‑vapor exposure, then static contact angle, hysteresis, tilt angle, and adhesion were measured. Micro‑ and nanostructures alone produce superhydrophobicity, but the combined hierarchical structure further enhances it and yields lower contact‑angle hysteresis than natural Lotus leaves.

Abstract

The superhydrophobic and self-cleaning leaves of Lotus (Nelumbo nucifera, Gaertn.) have been used as a model for the development of artificial biomimetic surfaces. The hierarchical structure of the Lotus leaf has been recreated to characterize the influence of hierarchical roughness on superhydrophobicity and adhesion. Hierarchical structures were fabricated by a fast and precise molding of the Lotus leaf microstructure, and self-assembly of the natural Lotus wax deposited by thermal evaporation to create the wax tubules nanostructures. Tubule formation was initiated by exposure of the specimens to a solvent vapor phase at a selected temperature. In order to study the influence of structures at different scale sizes on superhydrophobicity, a flat surface, microstructured Lotus leaf replica and a micropatterned Si replica, and a nanostructure were fabricated. Static contact angle, contact angle hysteresis, tilt angle and adhesive forces were measured. The data show that microstructures and nanostructures lead to superhydrophobicity, whereas hierarchical structures further improve this property and show low contact angle hysteresis, superior to that of the natural Lotus leaves.