Compression-torsion coupling behaviours in double-helix nanofibers assembled from negatively curved nanographenes

Abstract

The recently synthesised one-dimensional (1D) double-helix nanofibers that are self-assembled from negatively curved nanographenes, i.e., 1-H nanofibers are expected to have new applications in materials science and biology. In this paper, the mechanical behaviours of 1-H nanofibers are investigated by using molecular dynamics simulations. 1-H nanofibers are found to possess a Young’s modulus comparable to that of conventional cup-stacked carbon nanofibers. Meanwhile, a large plastic deformation is observed in the axially stretched 1-H nanofibers before their final breaking. In addition, 1-H nanofibers possess a bending stiffness significantly larger than that of many other 1D nanomaterials, making 1-H nanofibers behave more like an elastic rod or beam. More importantly, a unique compression-torsion coupling behaviour is observed in 1-H nanofibers, which is strongly dependent on the rotation direction. Specifically, when 1-H nanofibers are rotated along the helix direction, a residual tensile stress or, equivalently, an axial contraction is generated. However, no significant compression-torsion coupling behaviour is observed in 1-H nanofibers rotated along the direction reverse to helix. Furthermore, due to the compression-torsion coupling effect, a unique helical buckling behaviour can occur in 1-H nanofibers under pure axial compression, which is totally different from the conventional Euler buckling behaviour observed in many other 1D nanomaterials.