Mechanics of robust adhesion of smooth biological attachment pads on rough surfaces

Recent studies on geckos attachment structure revealed that robust adhesion on rough surfaces can be achieved by nanoscale hairy structures. Clearly, this may not be the only strategy for robust adhesion since smooth attachment systems, such as attachment pad of cicada, also exist in nature. To obtain a comprehensive understanding of the mechanics of robust adhesion on rough surfaces, adhesion between smooth attachment pad and periodically rough surfaces is studied by using a two-dimensional contact model. Our results show that the adhesion behavior between a smooth attachment pad and rough surfaces depends on dimensionless parameters and. While the former describes the flexibility of attachment pad, the latter characterizes the size of roughness asperity in contrast to the effective range of interaction forces. A phase diagram in terms of and is constructed for the condition of spontaneous full contact. Robust adhesion is feasible on surfaces with roughness up to microns as long as the flexibility parameter of the attachment pad satisfies. These findings not only shed light on adhesion of smooth attachment systems but would be of great value to the design of artificial devices for strong adhesion with rough surfaces.