Fabrication of anisotropic superhydrophobic surface based on the Nepenthes slippery zone

Abstract

Depending on its highly evolved structures that consist of microscale lunate cells and nanoscale wax coverings, the slippery zone of Nepenthes alata shows significant anisotropic superhydrophobicity, which has gradually become the biomimetic prototype for designing superhydrophobic surfaces. In this study, the authors constructed the structures of the slippery zone into equidistantly distributed greenhouses and array of cylinders, therefore obtaining a biomimetic model of an anisotropic superhydrophobic surface. The greenhouses were printed using ultraviolet-cured material, via 3D printing, and then flake graphite was selected as a substitute for the array of cylinders (wax coverings) and was absorbed onto the printed greenhouses by using high-voltage electrostatic absorption technology. The contact/sliding angle was measured to verify the anisotropic superhydrophobic effect of the fabricated sample. The contact angle increases significantly with an increase in the greenhouse density (l/L value) and achieves a value of 152.6 ± 0.6° when l/L is 0.8, and the sliding angle toward bottom and top shows values of 3.07 ± 0.26° and 5.69 ± 0.24°, respectively. These results indicate that the fabricated sample has anisotropic superhydrophobicity. Therefore, this study provides a simple and low-cost approach for the biomimetic fabrication of anisotropic superhydrophobic surfaces.