Interactions, friction and lubrication between polymer-bearing surfaces

Polymers that are adsorbed on a surface, or grafted to it (so-called polymer brushes), generally adopt extended configurations, For this reason forces between polymer-bearing surfaces are long-ranged, and are largely determined by steric interactions between molecules on the opposing layers. When two polymer-bearing surfaces are compressed and made to slide past each other, the frictional forces between them are determined by several different factors. The reduction of friction by polymer brushes occurs because such brushes can support a large load while maintaining a very fluid interface due to limited mutual interpenetration. At the highest pressures, slip reverts from the mid-plane to the polymer-substrate interface. Functionalized polymers with specifically attractive groups can lead to frictional dissipation on sliding which is modulated by the breaking and reforming of bonds. Detailed understanding of polymer-modulated friction may be obtained by taking due account of the polymer dynamics, surface structure and topology, and their specific surface attachment.