Chirality-Dependent and Intrinsic Auxeticity for Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) have superior mechanical properties which originate from a strong C-C covalent bond and unique nanostructure. Chirality, one of the helical structural parameters of SWCNTs, leads to differences in mechanical performance. In this work, molecular dynamics (MD) simulation was performed to analyze engineering Poisson's ratio (EPR) and incremental Poisson's ratio (IPR) of SWCNTs with different chiral angles, respectively, under tensile and compressive load, as well as the chiral effect on rigidity. We reported the minimum EPR for (4, 1) SWCNT and obtained the distribution and trend of EPR which is dependent on chiral index m. In addition, a new observation showed two exactly opposite trends of EPR existing not only in tension and compression but also in the longitudinal and radial directions. Furthermore, we found that the critical strain, over which SWCNT would be auxetic, ranged from 6% to 18% and was also chirality-dependent. Three representative SWCNTs with chiral angle of 0 degrees (zigzag), 10.89 degrees (chiral), and 30 degrees (armchair) were selected for the mechanism study of auxeticity. Finally, a method of the contribution to radial strain for two main deformation modes proposed in this paper could well explain the negative IPR phenomenon.

Automated summary

This study analyzed the engineering Poisson's ratio (EPR) and incremental Poisson's ratio (IPR) of single-walled carbon nanotubes (SWCNTs) with different chiral angles and investigated the effect of chirality on rigidity. It was found that SWCNTs with different chiral angles exhibited different mechanical properties in terms of EPR and IPR in tension, compression, longitudinal, and radial directions. The critical strain for auxeticity was also found to be chirality-dependent. Additionally, a method for explaining the negative IPR phenomenon was proposed based on the contribution to radial strain.