Influence of hydroxyls at interfaces on motion and friction of carbon nanotube by molecular dynamics simulation

Abstract

Understanding how the groups at interface influence the friction of carbon nanotubes can provide reference for their applications. In this paper, we investigate the influences of hydroxyls on motion and friction of carbon nanotube on graphite substrate by molecular dynamics simulation. The simulation cases include the ideal vertical carbon nanotube on the ideal graphite substrate, the ideal vertical carbon nanotube on the graphite with hydroxyls on the top layer, the carbon nanotube and the graphite both with hydroxyls on the surface. The results show that the lateral force of carbon nanotube changes when hydroxyls are introduced into the interfaces. If hydroxyls are only on the graphite, the fluctuation of lateral force increases obviously. The reason can be attributed to the increase of atomic surface roughness. Moreover, due to the small contact area between vertical aligned carbon nanotube and substrate, the mean friction becomes raised with hydroxyl content increasing, which is different from the conclusion obtained from silicon tip sliding on graphene with hydrogen on the surface. In that case, owing to the large contact area, the mean friction of tip reaches a maximum value at hydrogen content in a range between 5 and 10% because of the competition between the increase in the number of hydrogen atoms and the weakening of the interlock due to the increase in separation of tip from substrate. Hydrogen bond and Coulomb force appear between interfaces when hydroxyls are both on carbon nanotube and on graphite, which significantly increases friction force on carbon nanotube. And slip interfaces translate rapidly from between carbon nanotube and graphite into between graphite layers. Like the case with hydroxyls only on the graphite, the sliding of carbon nanotube perpendicular to the initial velocity also occurs when carbon nanotube and graphite are both with hydroxyls. This phenomena can be explained as the fact that the introduction of hydroxyls breaks the equilibrium of the force on the carbon nanotube in the Y direction. Moreover, the random distribution of hydroxyls causes the random motion of the carbon nanotube.