Towards the development of nanosprings from confined carbyne chains

The synthesis of long and stable carbyne chains inside carbon nanotubes (CNTs) have recently drawn renewed attention to this linear one-dimensional carbon allotrope. Carbyne's mechanical properties are predicted to exceed that of CNTs and graphene, making it a very suitable structural component for many nanoscale applications. While carbyne's mechanical behavior under tensile loading is excellent, this carbon chain readily buckles under compressive loading. Taking this effect into account, here we study the compressive behavior of carbyne chains under the bracing effect of confinement in small diameter CNTs such as (5,5) and (6,6) and the formation of helix-shaped springs of carbyne under compressive loading in larger diameter CNTs such as (7,7) and (8,8), using molecular dynamics simulations (MD). The Young's modulus of confined carbyne chains under compression was estimated in average to be 4029 GPa when confined in (5,5) CNT and 3858 GPa when confined in (6,6) CNT, showing slight increases with chain length. We found that for looser confinements carbyne chains can buckle into a coiled helix-shaped spring with properties that depend on confinement radius and chain length. The behavior of these nanosprings follows Hooke's law and may be envisaged for applications in nanodevices.