Structural and Helix Reversal Defects of Carbon Nanosprings: A Molecular Dynamics Study

Due to their chiral structure, carbon nanosprings possess unique properties that are promising for nanotechnology applications. The structural transformations of carbon nanosprings in the form of spiral macromolecules derived from planar coronene and kekulene molecules (graphene helicoids and spiral nanoribbons) are analyzed using molecular dynamics simulations. The interatomic interactions are described by a force field including valence bonds, bond angles, torsional and dihedral angles, as well as van der Waals interactions. While the tension/compression of such nanosprings has been analyzed in the literature, this study investigates other modes of deformation, including bending and twisting. Depending on the geometric characteristics of the carbon nanosprings, the formation of structural and helix reversal topological defects is described. During these structural transformations of the nanosprings, only van der Waals bonds break and recover, but breaking or recovery of covalent bonds does not take place. It is found that nanosprings demonstrate a significantly higher coefficient of axial thermal expansion than many metals and alloys. Under axial compression, Euler instability leads to lateral bending with continuous deformation of the nanospring axis at relatively low compression, while at high compression, bending kinks form. Various types of topological defects form on the instantly released nanospring during its relaxation from a highly stretched configuration. These results are useful for the development of nanosensors operating over a wide temperature range.