Hindered rolling and friction anisotropy in supported carbon nanotubes

TL;DR

This study combines theory and experiments to reveal that supported carbon nanotubes exhibit higher transverse friction due to hindered rolling, which impacts their assembly and sorting strategies.

Contribution

It provides new insights into the anisotropic frictional behavior of supported CNTs, highlighting the role of hindered rolling in friction anisotropy.

Findings

Transverse friction coefficient exceeds parallel in supported CNTs.

Hindered rolling explains the higher transverse friction observed.

Chiral CNTs show reduced frictional dissipation in parallel sliding.

Abstract

Carbon nanotubes (CNTs) are well known for their exceptional thermal, mechanical and electrical properties. For many CNT applications it is of the foremost importance to know their frictional properties. However, very little is known about the frictional forces between an individual nanotube and a substrate or tip. Here, we present a combined theoretical and experimental study of the frictional forces encountered by a nanosize tip sliding on top of a supported multiwall CNT along a direction parallel or transverse to the CNT axis. Surprisingly, we find a higher friction coefficient in the transverse direction compared with the parallel direction. This behaviour is explained by a simulation showing that transverse friction elicits a soft 'hindered rolling' of the tube and a frictional dissipation that is absent, or partially absent for chiral CNTs, when the tip slides parallel to the CNT axis. Our findings can help in developing better strategies for large-scale CNT assembling and sorting on a surface.