Achieving enhanced and tunable adhesion via composite posts

Surfaces with enhanced and tunable adhesion have a variety of applications, including microtransfer printing of semiconductor elements, material handling in manufacturing, and gripping surfaces on climbing robots. Traditionally, schemes to achieve tunable adhesion have relied on fabricating arrays of posts or fibers with complex geometries, such as angled posts terminated by wider caps. Here, we describe an alternative to post structures with complex geometries through the use of composite posts that consist of a stiff core and a compliant shell. Posts consisting of a stiff core and compliant shell have enhanced adhesion under normal loading, and the pull-off can be reduced via the application of shear. The adhesion mechanics of composite posts are demonstrated here through a combination of finite element simulations and experimental measurements on individual millimeter-scale posts.