Adhesion and Friction Enhancement of Film-Terminated Structures against Rough Surfaces

A number of biomimetic and bioinspired micron-scale surface structures have been developed in recent years with unique surface properties such as highly enhanced and switchable adhesion and friction against smooth surfaces. However, few studies have examined the effect of roughness on mechanisms for property enhancement, although this is of critical importance for applications. Here, we investigate the effect of roughness on adhesion and friction of a family of film-terminated fibrillar and ridge/channel microstructures. Although increasing roughness uniformly attenuates adhesion and friction, we find that the film-terminated structures maintain their enhancement compared to flat controls against a variety of rough surfaces (including natural stones). The principal mechanisms underlying property enhancement against smooth surfaces remain operative against rough surfaces. We show how the effect of roughness on surface mechanical properties of structured surfaces can be understood as a combination of known effects due to structure and roughness.