Effect of Pretension on the Peeling Behavior of a Bio-inspired Nanofilm and a Hierarchical Adhesive Structure

Abstract

Inspired by the reversible adhesion behaviors of geckos, the effects of pretension in a bio-inspired nanofilm and a hierarchical structure on adhesion are studied theoretically. In the case with uniformly distributing pretension in a spatula-like nanofilm under peeling, a closed-form solution to a critical peeling angle is derived, below or above which the peel-off force is enhanced or reduced, respectively, compared with the case without pretension. The effects of nonuniformly distributing pretension on adhesion are further investigated for both a spatula-like nanofilm and a hierarchical structure such as gecko’s seta. Compared with the case without pretension, the pretension whether uniform or nonuniform can increase the adhesion force not only for the spatula-like nanofilm but also for the hierarchical structure at a small peeling angle, while decreasing it at a relatively large peeling angle. Furthermore, if the pretension is large enough, the effective adhesion energy of a hierarchical structure tends to vanish at a critical peeling angle, which results in spontaneous detachment of the hierarchical structure from the substrate. The present theoretical predictions can not only give some explanations on the existing experimental observation that gecko’s seta always detaches at a specific angle and no apparent adhesion force can be detected above the critical angle, but also provides a deep understanding for the reversible adhesion mechanism of geckos and be helpful for design of biomimetic reversible adhesives.