Experimental Research On Detachment Mechanism Of Anti-insect-adhesion Plant Surfaces

Insects in nature, generally, are adept at adhering to various rough and smooth surfaces including numerous plant leaves taking advantage of their specific foot structures. Meanwhile, some plant surfaces can refrain from insects'adhesion and even capture those guests by its unique characteristics to get nutrients. Here, we investigate the anti-adhesion mechanism and detachment stability of the waxy zone of nepenthes in various air humidity conditions, using colloid probes. This research provides a theoretical foundation for design and preparation of bionic anti-adhesion surfaces.The micro-topography and geometrical parameters of the waxy slippery zone of the nepenthes surface are characterized by atomic force microscope (AFM) and environment scanning electron microscope (ESEM). Adhesion and friction forces of the waxy zone surface are measured using colloid probe simulation method, and measurement results are compared with those of polishing papers with different roughness values. Considering the effect of surface physicochemical properties on its adhesion ability, contact angles of polar (water) and non-polar (diiodomethane) liquids on the waxy zone surface and polishing papers with a similar roughness are measured by contact angle measuring device. The results show that a single crystal of waxy zone is of the mechanical stability, thus disclaiming the contamination hypothesis. The contact area at the interface can be reduced efficiently by the surface roughness of waxy zone, which, to some extent, decreases its adhesion and friction forces. The super-hydrophobic property, combined with the low surface energy of the waxy zone, forming an anti-adhesion effect on the nepenthes waxy slippery zone, is another key factor in reducing the surface adhesion and friction forces.Additionally, to investigate the detachment stability of nepenthes waxy slippery zone, colloid probe simulation method is used to measure the adhesion and friction of the waxy zone surface in a range of air humidity. Smooth glasses and several plant surfaces with typical architectures (smooth two-dimensional layers of wax, low cuticular folds, and high cuticular folds) are employed to be references. The results show that smooth two-dimensional wax layers of Ilex aquifolium leaf surface, possessing an enhanced detachment property in dry ambient air, can prevent the formation of capillary bridge around low humidity ambient air. The Litchi chinensis leaf surface with low cuticular folds presents a better anti-adhesion character and ability of rejecting capillary bridge in a wider humidity range than two-dimensional wax layers; High cuticular folds of Cyclamen persicum leaf and three-dimensional wax crystals of nepenthes surface are able to drive away water vapor around the contact area, thus appear a high-efficiency anti-adhesion function either in dry or high humidity ambient air. The architecture of nepenthes waxy surface shows a superior anti-adhesion effect, compared with that of Cyclamen persicum leaf. Furthermore, wet contact models with different typical plant surface architectures are proposed to interpret the experimental phenomenon.