Predicting mechanical properties of carbon nanosprings based on molecular mechanics simulation

A carbon nanospring (CNS) is formed by coiling a single-walled carbon nanotube around a cylindrical surface with a uniform pitch length and a uniform spring rise angle. Using the displacement-controlled tension method, the mechanical properties of small-radius and large-radius CNSs are investigated based on a molecular mechanics (MM) simulation. The tension behaviour of a small-radius CNS with more turns is similar to that of a mechanical spring. The spring stiffness of a three-turn CNS is calculated to be 0.36 N/m with a maximum of 38% elongation for its elastic deformation. Although a large-radius CNS with more turns cannot be uniformly stretched along its axial direction, it has excellent flexibility without structural damage even when the CNS is stretched to a carbon nanotube (CNT). It is found that the spring stiffness of a large-radius CNS with one turn and two turns are both nonlinear. For a one-turn CNS, the stiffness first decreases and then increases with the tension displacement and less influenced by the chiral type.