The Formation of Viscous Surface Films by Polymer Solutions: Boundary or Elastohydrodynamic Lubrication?

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Abstract
The film-forming properties of a range of polymer solutions have been studied down to very thin film thickness using ultrathin film interferometry. It has been found that, at very slow rolling speeds, some polymers generate much thicker films than predicted from theory. It appears that these polymers form adsorbed layers between three and 15 nanometers thick on the two solid surfaces. These layers have a viscosity many 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-type film much thicker than predicted from the viscosity of the bulk lubricant. As the speed is raised the contact emerges from this boundary layer and reverts to elastohydrodynamic behavior based upon the viscosity of the bulk polymer solution.