Double-Walled Carbon Nanotubes with Dynamic Strength of over 90 GPa Enhanced by Intershell Friction.

Low-dimensional ultra-strong nanomaterials have attracted great anticipation for applications under extreme dynamic conditions. A photocatalytic method is developed to selectively cut off the outer shell of double-walled carbon nanotubes (DWCNTs), achieving non-contact measurement of intershell friction with both high temporal and spatial resolutions at high sliding velocities under optical microscope. The intershell friction linearly increases with the sliding velocity, with a slope related to intershell distance and chirality of DWCNTs. The maximum measured friction reaches 194.1 ± 7.3 nN at a sliding velocity of 977 mm s, a value comparable to the tensile force (≈450 nN) for breaking the outer shell. Molecular dynamics simulations indicate that the velocity-dependent intershell friction is related to dynamic localized commensurate contacts. The friction-induced "intershell locking" enhances the effective dynamic strength of DWCNTs from 64.8 ± 3.4 GPa to 90.1 ± 4.0 GPa at a tensile strain rate of 3300 s. This study reveals anomalous friction mechanisms at nanoscale and demonstrates promising application of DWCNTs as ultra-strong materials.