Axial-Strain-Induced Torsion in Single-Walled Carbon Nanotubes

Using classical molecular dynamics and empirical potentials, we show that the axial deformation of single-walled carbon nanotubes is coupled to their torsion. The axial-strain-induced torsion is limited to chiral nanotubes—graphite sheets rolled around an axis that breaks its symmetry. Small strain behavior is consistent with chirality and curvature-induced elastic anisotropy (CCIEA)—carbon nanotube rotation is equal and opposite in tension and compression, and decreases with curvature and chirality. The largestrain compressive response is remarkably different. The coupling progressively decreases, in contrast to the tensile case, and changes its sign at a critical compressive strain.

To rule out the "artificial effects"of MD simulations, geometrically nonlinear FEM analysis on an analogus of elastic beam frame is perfomred to confirm the above results. It proves to be effects of symmetry broken.

The response opens up the possibility of high quality, tunable nanoscale actuators, oscillators or clocks, and nanomotors, in turn driven by electro-, thermo-, chemico-, and optico-mechanical coupling in appropriately functionalized chiral nanotubes, nanowires, and nanofilaments. The elimination of the need of electrostatic actuation of the rotation motion is a significant step forward as it facilitates fabrication of single-step, integrated CNT-NEMS devices.

Carbon Nanotubes Turn Translation into Rotation