Deformation-and rupture-controlled friction between PDMS and a nanometer-scale SiO_(x) single-asperity

This work investigates the friction between polydimethylsiloxane(PDMS)and silicon oxide(SiO_(x))in single asperity sliding contact by atomic force microscopy(AFM).Two friction dependences on the normal force are identified:a tensile regime and a compressive regime of normal forces.In the compressive regime,friction is governed by the shear deformation and rupture of junctions between PDMS and SiO_(x).In this case,the shear strengthτ≈10 MPa is comparable with the cohesive strength of PDMS under compressive loading.In contrast,friction in the tensile regime is also affected by the elongation of the junctions.The single SiO_(x)-asperity follows a stick–slip motion on PDMS in both normal force regimes.Statistical analysis of stick–slip as a function of the normal force allows determining the necessary amount of energy to break a SiO_(x)/PDMS junction.Friction between a SiO_(x)-asperity and a PDMS surface can be rationalized based on an energy criterion for the deformation and slippage of nanometer-scale junctions.