A tribological study of double-walled and triple-walled carbon nanotube oscillators

Abstract

We reported in a previous study (Zhao et al 2003 Phys. Rev. Lett. 91 175504) that energytransfer from the orderly intertube translational oscillation to intratube vibrational modesfor an isolated system of two coaxial carbon nanotubes at low temperatures takes placeprimarily via two distinct types of collective motion of the carbon nanotubes, i.e., off-axialrocking motion of the inner tube and radial wavy motion of the outer tube, andthat these types of motion may or may not occur for such a system, dependingupon the amount of the initial extrusion of the inner tube out of the outer tube.Our present study, using micro-canonical molecular dynamics (MD), indicatesthe existence of an energy threshold, largely independent of system sizes andconfigurations, for a double-walled nano-oscillator to deviate from the intertubetranslational oscillation and thus to encounter significant intertube friction. Thefrictional forces associated with several distinct dissipative mechanisms are all foundto exhibit no proportional dependence upon the normal force between the twosurfaces in relative sliding, contrary to the conventional understanding resultingfrom tribological studies of macroscopic systems. Furthermore, simulation hasbeen performed at different initial temperatures, revealing a strong temperaturedependence of friction in the early phase of oscillation. Finally, our studies ofthree-walled nano-oscillators show that an initial extrusion of the middle tubecan cause inner-tube off-axial instabilities, leading to strong frictional effects.