Tribological Behavior of Aligned Single-Walled Carbon Nanotubes

An abnormal friction law refers to the case where the friction force does not increase monotonically with the normal pressure. We investigate the possibility of abnormal tribological behavior for two surfaces coated with aligned single-walled carbon nanotubes (SWCNTs). Detailed molecular dynamics simulations for aligned SWCNTs predict modulated variation between the kinetic friction force and the applied pressure. The interacting SWCNTs float with respect to each other at about the equilibrium separation of van der Waals interaction, and the wavy contact profile breaks the symmetry of the contacting cross-section. Cases treated by molecular dynamics simulation include two aligned (10,10) SWCNTs with periodic end conditions, and a stack of three aligned (10,10) SWCNTs with free end boundary conditions. A continuum theory based on the wall deflection under finite deformation, in combination with an adhesion criterion similar to the JKR theory, on the other hand, predicts a declining law between the frictional force and the pressure. The correlation of the data obtained through the atomistic and the continuum approaches relies on a deeper understanding on the friction process among SWCNTs.