Tribological properties of vertically aligned carbon nanotube arrays and carbon nanotube sponge

Abstract

Carbon nanotube (CNT) films showing excellent mechanical and frictional performances are one of the most competitive candidates for fabricating functional surfaces; in particular, the bulk form of the forest-like vertical aligned CNT (VACNT) film and CNT sponge are idea candidates for making a flexible solid lubricant surface due to the fact that their porous network has a high potential to experience large deformation. In this article, the frictional behavior of the VACNT and CNT sponge against a millimeter scale copper sphere has been studied under various conditions within a home-built system. Due to the intrinsic mechanical instability of VACNTs, a higher friction state than the CNT sponge has been observed, and beyond that, VACNTs typically show a run-in process as a function of sliding circle caused by the formation and rearrangement of quasi-periodic cracks; on the contrary, the friction of the CNT sponge is very stable. In addition, we have pinpointed the effects of sliding velocity, relative humidity, and temperature on friction. The sliding friction was observed to be independent of the velocity and temperature; however, due to the increase in capillary force, friction increases with the increase in relative humidity.