THE FORMATION OF VISCOUS SURFACE-FILMS BY POLYMER-SOLUTIONS - BOUNDARY OR ELASTOHYDRODYNAMIC LUBRICATION

The film-forming properties of a range of polymer solutions have been studied down to very thin film thickness using ultrathin film interfer ometry. It has been found that, at very slow rolling speeds, some poly mers generate much thicker films than predicted from theory. It appear s that these polymers form adsorbed layers between three and 15 nanome ters thick on the two solid surfaces. These layers have a viscosity ma ny times higher than that of the bulk solution. Therefore, under slow speed, low film thickness conditions, the contact effectively operates within a viscous boundary layer, generating an elastohydrodynamic-typ e film much thicker than predicted from the viscosity of the bulk lubr icant. As the speed is raised the contact emerges from this boundary l ayer and reverts to elastohydrodynamic behavior based upon the viscosi ty of the bulk polymer solution.