Stiffer Is\nStickier: Adhesion in Elastic Nanofilms

When two objects are brought into contact, separating\nthem typically\nrequires overcoming a detachment force. While this adhesion-induced\nforce is vital for thin film materials in a range of nature and engineering\nsystems, its quantitative understanding remains elusive due to the\ncomplex interplay between nonlinear deformation and adhesion. Here\nwe perform controlled experiments and develop formal theories for\nthe detachment force in a canonical configuration: separation of a\nsphere from an elastic graphene film. We observe that applying tension\nto the film can increase both its apparent out-of-plane stiffness\nand its detachment force, a behavior that cannot be explained by macroscopic\nadhesion theories. We attribute this unusual “stiffer-stickier”\nbehavior to long-range intermolecular forces and demonstrate that\nit is a general phenomenon for elastic nanofilms, explainable through\na multiscale theory that we develop. The ideas introduced here offer\na generic strategy to understand the adhesion of slender structures\nacross various length scales.