Evaluation of Friction Behavior and Contact Area Dependence at the Micro and Nanoscales

In this work, we have compared the friction behavior of two different materials (a) mica and (b) ultra-high molecular weight polyethylene (UHMWPE) at two length scales. The friction experiments were carried out at the nanoscale with an atomic force microscope (AFM) and at the microscale, with a custom-built microtribometer. The material interface (Si₃N₄ probe) and the environmental conditions (RH < 10%) were kept the same at both the scales. The friction data obtained were analyzed for dependence on normal load or contact area, based on which, a coefficient of friction has been reported or an appropriate contact mechanics theory was applied and an interfacial shear strength value was calculated for the material pair. Friction between a silicon nitride and UHMWPE interface resulted in contact area dependence at both the length scales, for the applied load ranges of our experiment. Friction between silicon nitride and mica at the nanoscale showed an initial nonlinearity and then exhibited damage and linearity with normal load beyond certain loads. At the microscale, the mica-silicon nitride interface resulted in a linear friction behavior.