(175e) Morphology of Soft, Stratified and Slippery Contact

We present the first experimental observation on effects of surface slip caused by roughness on the morphology and dynamics of soft contacts. We disentangle the contributions of surface stratification and slip through measurement of absolute fluid film thickness and comparing with theory based on linear elasticity and fluid lubrication. We show that stratification leads to deformation profiles that are drastically different from those observed for elastic half-space (wimples). The coupled effect of surface slip and elasticity can lead to trapped fluid pockets between surfaces in contact. The contact morphology between soft coatings has important implications in tribology, interfacial rheology, pressure sensitive adhesives, and in biology. In the context of bio-inspired adhesives, the surface structure and mechanical properties of soft coatings are engineered to maximize the contributions of surface forces (such as van der Waals interactions). Here we see that the dynamics of contact formation, and associated elastic deformation, can prevent physical contact therefore could play an important role in the adhesive performance of bio-inspired adhesives. Similarly, trapped fluid during the bonding of pressure sensitive adhesives could lead to poor bond formation and weaker performance. Lastly, with the absence of surface profile information, the interplay between stratification and roughness could lead to misinterpretation of dynamic surface forces measurements.