title: Surface tension regularizes the crack singularity of adhesion.
abstract: The elastic and adhesive properties of a solid surface can be quantified by indenting it with a rigid sphere. Indentation tests are classically described by the JKR-law when the solid is very stiff, while recent work highlights the importance of surface tension for exceedingly soft materials. Here we show that surface tension plays a crucial role even in stiff solids: Young's wetting angle emerges as a boundary condition and this regularizes the crack-like singularity at the edge of adhesive contacts. We find that the edge region exhibits a universal, self-similar structure that emerges from the balance of surface tension and elasticity. The similarity theory is solved analytically and provides a complete description of adhesive contacts, by which we reconcile global adhesion laws and local contact mechanics.
authors.affiliation: Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands. j.h.snoeijer@utwente.nl.
authors.forename: Stefan
authors.initials: S
authors.lastname: Karpitschka
authors.affiliation: Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands. j.h.snoeijer@utwente.nl.
authors.forename: Leen
authors.initials: L
authors.lastname: van Wijngaarden
authors.affiliation: Physics of Fluids Group, Faculty of Science and Technology, Mesa+ Institute, University of Twente, 7500 AE Enschede, The Netherlands. j.h.snoeijer@utwente.nl and Mesoscopic Transport Phenomena, Eindhoven University of Technology, Den Dolech 2, 5612 AZ Eindhoven, The Netherlands.
authors.forename: Jacco H
authors.initials: JH
authors.lastname: Snoeijer