Using microfluidics to control soft adhesion

We demonstrate that the inclusion of subsurface micro-fluidic features in a soft polymer surface, whose internal pressure can be varied, can be used to modify the effective radius of curvature of the contact and thus switch the magnitude of the adhesion of the surface to a harder counterface from one state to another – in other words to control the ‘stickiness’ of the surface. In these circumstances adhesion depends on van der Waal forces and can be described by the classic treatment of Johnson Kendall and Roberts [1] who added the influence of surface energy to that of elastic deformation in the analysis of the contact between a loaded sphere and a smooth flat. In addition, we demonstrate that appropriate surface features, viz. relatively slender ‘fibrils’, can enhance the ability of a such a soft surface to adhere to a hard but macroscopically rough counterface while still maintaining the possibility of switching from one level to another. Conversely, stiffer more conical surface features can suppress adhesion even against a smooth counterface.