Nano-friction, stick-slip and pull-out forces in nanotube-multiwalls, -composites and -bundles

An analysis to understand and quantify the phenomenon of nano-friction and stick-slip observed during sliding of adjacent shells in multiwalled carbon nanotubes is presented. The contact force and shear stress are found to be strongly non-uniform along the contact length, as a consequence of boundary edge effects. In this context, the theoretically predicted superlubricity state seems to be unrealistic for finite-sized objects. We demonstrate that such boundary effects dominate sliding at nanoscale for finite-sized object, making it more similar to a fracture phenomenon than to classical friction. The relationship between contact-force and contact-length is found to be asymptotic, explaining the difference in the observations on nanotube sliding reported in the literature. The pull-out force is quantified and found to asymptotically approach a constant value, rather than to be proportional to the contact surface area, as frequently assumed. The analysis is finally applied to predict the strength and toughness of nanotube-based composites and nanotube-bundles