Energy Approach to Understand Contact Mechanics on Rough Surfaces

Understanding the deformation of elastic solids on rough surfaces is crucial for soft-hard contacts at different scales of applications such as biomedical adhesives, tire traction, soft robotics and even micro- or nano-electromechanical devices. It has been experimentally demonstrated that the apparent work of adhesion for a soft material brought in contact with rough surfaces is lower than the intrinsic work of adhesion. During separation, there is energy loss commonly attributed to viscoelastic dissipation, termed as adhesion hysteresis. Here, with
experimentally controlled elastic modulus, roughness and surface chemistry, we demonstrate that the reduction in work of adhesion is equal to the energy required to achieve conformal contact. Further, the energy loss during contact and removal is equal to the product of the
intrinsic work of adhesion and the true contact area. These findings provide a simple mechanism to quantitatively link the widely observed adhesion hysteresis to roughness rather than viscoelastic dissipation.