Huge stretchability and reversibility of helical graphenes using molecular dynamics simulations and simplified theoretical models

Abstract

Helical nanostructures, like nanosprings, made from carbon-based materials have broad promising applications in mechanical nanodevices and energy-absorbing materials. However, it is a big challenge to reveal the mechanism of their excellent mechanical properties due to the lack of theoretical models. Here we report the huge stretchability and reversibility of helical graphenes (HGs) using molecular dynamics (MD) simulations. Simplified theoretical models based on interlayer van der Waals (vdW) interactions are developed to predict the tensile properties of different-size HGs in three elastic stages including the initial deformation, stable delamination and elastic deformation. During the tensile process, the vdW interactions between adjacent free coils play a key role in the initial deformation and delamination stages, while the tensile behavior is dominated by the stretching of carbon-carbon bonds in the elastic deformation stage. The obtained theoretical results agree well with those from present MD simulations. Meanwhile, both the critical force in the initial deformation stage and the critical elastic force in the elastic deformation stage decrease with increasing temperature. In particular, the mechanical behavior of HGs under cyclic loading shows obvious hysteresis loops, which produce large energy dissipation due to the recovery of interlayer vdW interactions. These findings should be of great help towards understanding the stability and reliability of these helical structures, and giving an insight to design a new generation of nanodevices.