LONG-RANGED SURFACE FORCES - THE STRUCTURE AND DYNAMICS OF POLYMERS AT INTERFACES

Polymers that attach at solid-liquid interfaces can considerably modify the long-ranged forces acting between surfaces. Over the past decade or so these forces have been studied directly using a surface-force-balance approach, and the equilibrium force laws between two polymer-bearing surface interacting across a liquid medium are reasonably well understood. Recently we have extended these studies to the case of surfaces with adsorbed and with grafted layers as they shear part each other. Our results suggest that the lateral forces depend on the extent of interpenetration of the opposing layers and on their relative shear velocities; they reveal a marked coupling between the normal forces and the shear velocity, beyond a certain critical value of the latter which is probably related to relaxation rates of the end-tethered chains. We find that while non-adsorbing but end-anchored polymer layers are stable with respect to shear and compression, they can be rapidly replaced by addition of shorter polymers with the same adhering end-group.