Micro-morphological Models for Hydrophobicity on the Surface of Moth Wing

Abstract

The micro-morphology, wettability and chemical composition of the moth wing surfaces were investigated by a scanning electron microscope (SEM), a contact angle (CA) meter and a Fourier transform infrared spectrometer (FT-IR). The micro-morphological models for hydrophobicity on the wing surface were established on the basis of the Cassie-Baxter equation. The wetting mechanism was discussed from the perspective of biological coupling. The moth wing surfaces are composed of naturally hydrophobic material and display micro/nano hierarchical structures, including primary structure (micrometric scales), secondary structure (submicro longitudinal ridges and lateral bridges) and tertiary structure (nano stripes). The wing surfaces exhibit high hydrophobicity (CA 150~158°) and low adhesion (sliding angle 1~3°). The cooperative effect of material element and structural element contributes to the special wettability of the wing surface. In micro-dimension, the smaller the width and the bigger the spacing of the scale, the stronger the hydrophobicity of the wing surfaces. In nano-dimension, the smaller the height and the smaller the width and the bigger the spacing of the longitudinal ridge, the stronger the hydrophobicity of the wing surfaces. The micro/nano structural model provides CA predictions in good accord with the data measured. The result may bring inspiration for biomimetic design and preparation of smart interfacial materials and novel self-cleaning coatings. Keywords-micro-morphology; contact angle; hydrophobicity model; biomaterial; moth