Adhesion and size dependent friction anisotropy in boron nitride nanotubes

TL;DR

This study investigates how the frictional properties of boron nitride nanotubes depend on their size and adhesion, revealing that larger contact areas increase friction anisotropy and that BN-NTs have intermediate friction characteristics compared to carbon nanotubes.

Contribution

It demonstrates the size and adhesion dependence of friction anisotropy in boron nitride nanotubes and compares their tribological properties to carbon nanotubes, highlighting potential for extreme environment applications.

Findings

Friction anisotropy increases with nanotube-substrate contact area.

BN-NTs exhibit intermediate friction coefficients between different synthesis methods.

Larger contact area reduces the difference between transverse and longitudinal friction.

Abstract

The frictional properties of individual multiwalled boron nitride nanotubes (BN-NTs) synthesized by chemical vapor deposition (CVD) and deposited on a silicon substrate are investigated using an atomic force microscope tip sliding along (longitudinal sliding) and across (transverse sliding) the tube's principal axis. Because of the tube transverse deformations during the tip sliding, a larger friction coefficient is found for the transverse sliding as compared to the longitudinal sliding. Here, we show that the friction anisotropy in BN-NTs, defined as the ratio between transverse and longitudinal friction forces per unit area, increases with the nanotube-substrate contact area. Larger contact area denotes stronger surface adhesion, resulting in a longitudinal friction coefficient closer to the value expected in absence of transverse deformations. Compared to carbon nanotubes (C-NT), BN-NTs display a friction coefficient in each sliding direction with intermediate values between CVD and arc discharge C-NTs. CVD BN-NTs with improved tribological properties and higher oxidation temperature might be a better candidate than CVD C-NTs for applications in extreme environments.