Revisiting the contact splitting hypothesis : an effective route for enhancing adhesion on rough surface

Abstract

The contact splitting hypothesis (CSH) has been proposed for around 20 years, which suggests that the patterned or fibrillar surfaces enable very efficient biological attachment systems (e.g., Geckos’ seta). However, there is still a debate in academic community on the necessity of the CSH in man-made adhesives, since experiments have indicated that the non-fibrillar surface can also show strong adhesion. This study demonstrates that the surface roughness plays a key role in evaluating the influence of CSH on adhesion by a simple finite element (FE) model. The highly split structures are essentially required for strong adhesion on highly rough surface, but may in turn cause slight adhesion reduction on smooth surface due to the areal loss in the splitting process. With our results, the debate in CSH is explained as an incomplete understanding of an adhesive contact problem, in which the surface roughness is overlooked. Our results further sheds light on the natural selection that climbing animals with heavier body usually evolve finer adhesive structures on their pads, by considering both the surface roughness and its length scale dependence.