Enhanced stiffness of amorphous polymer surfaces under confinement of localized contact loads

For contact depths < 200 run from the free surface of amorphous polymers, the apparent mechanical stiffness is in excess of bulk elastic properties. This enhanced stiffness can be attributed to the dynamic formation of a mechanically distinct interphase at synthetic and biological polymer interfaces. In glassy polymers such as polystyrene, this enhanced stiffness is independent of molecular weight, processing route, and environmental conditions.