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Friction on solid polymer and nano-contacts

The aim is to imrove the knowledge in physics and mechanics mechanisms at the interface between a rigid tip and a rejuvenated glassy polymer. As the tip slides, the activation volume at this interface is estimated to a few nm3.
Tests were performed on rejuvenated polycarbonate surfaces, in a mean contact pressure range below the yield point and in dry friction (RH < 4%).
The rheological behaviour at the interface between a polymer surface and a rigid indenter during dry friction is linked to the local pressure and the roughness of the surface of the indenter. The rigid indenters are made of spherical glass from several radii whose surfaces are of two types: polished to tight tolerance (optical lenses) or nano-roughened (chemical etching), and experiments are made using our homemade scratch apparatus and our recent nanoscratch device. Millimetric tips were etched to have model roughnesses (from 5.5 rms nm to 140 rms nm). Below yield stress (pmean < 100MPa) the intrinsic friction coefficient follows a master curve for smooth indenters whereas nano-roughness monitors friction. To explain these experimental results an original modeling mixing local behaviours was developed based on the classical laws of contact mechanics and gives the basics to study confined polymer layers.

* A. Rubin, C. Gauthier, R. Schirrer, “Analysis of the effect of nano-roughness on the friction of a vitreous polymer”, Wear 303, 40-48 (2013) ;doi:10.1016/j.wear.2013.02.021.
* A. Rubin, C. Gauthier, R. Schirrer, “The friction coefficient on polycarbonate as a function of the contact pressure and nanoscale roughness”, J. Polymer Sciences Part B: Polymer Physics 50, 580–588 (2012) ; doi: 10.1002/polb.23046.