Buckling of double-walled carbon nanotubes under compression and bending: Influence of vacancy defects and effect of high-temperature annealing

We study by molecular dynamics simulations the effect of vacancy defects on mechanical properties of double-walled carbon nanotubes (DWCNTs) under compression and bending. Our results show that the critical buckling strain under compression and critical buckling angle under bending generally decrease with increasing defect density, but the detailed buckling behavior is sensitive to defect distribution patterns (e.g., whether vacancies are on the inner or outer wall, at separate sites or clustered together). Interestingly, upon high-temperature annealing, vacancy defects undergo structural reconstructions and, in particular, form interlayer bonds that significantly improve the load carrying capability of the DWCNTs under compressive and bending deformation. These results provide new insights into the role of vacancy defects in determining the buckling behavior of multi-walled carbon nanotubes (MWCNTs); they also suggest that high-temperature annealing is an effective tool for defect engineering to improve mechanical properties of MWCNTs. The present study reveals trends and underlying mechanisms with regard to the buckling of DWCNTs under different loading conditions, and the obtained results may provide a useful guide for post-synthesis treatment and application of MWCNTs.