The friction coefficient on polycarbonate as a function of the contact pressure and nanoscale roughness

During dry friction the rheological behavior at the interface between a polymer surface and a rigid indenter is linked to the local pressure and the roughness of the surface of the indenter. This study on polycarbonate reports experimental results obtained at ambient temperature using rigid, spherical glass indenters of various radii. In a first step, a plot of the experimental friction coefficient mu versus the mean contact pressure pmean showed that below the yield stress (pmean < 100 MPa) the intrinsic friction coefficient follows a master curve for smooth indenters. In a second step, roughened indenters were prepared by chemical etching, which allowed the monitoring of nanoscale roughness parameters. From 5.5 to 140 nm Rrms, the friction coefficient mu progressively fell to a plastic-like constant value, indicating that the nanoroughness mediates the friction. These results form the basis for a study of the rheology of confined polymer layers. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012