Optimizing Structural and Mechanical Properties of Coiled Carbon Nanotubes with NSGA-II and Reactive Molecular Dynamics Simulation

Abstract

Coiled carbon nanotubes (CCNTs) have increasingly become a vital factor in the new generation of nanodevices and energy-absorbing materials due to their outstanding properties. Here, the multiobjective optimization of CCNTs is applied to assess their mechanical properties. The best trade-off between conflicting mechanical properties (e.g., yield stress and yield strain) is demonstrated and the optimization of the geometry enables us to find the astonishing CCNTs with a stretchability of 400%. These structures have been recognized for the first time in the field. We derived several highly accurate analytical equations for the yield stress and yield strain by the implementation of multiobjective optimization and fitting a theoretical model to the results of molecular dynamics (MD) simulations. The optimized structures are highly resilient because of two distinct deformation mechanisms depending on the dimensions of CCNTs. For small CCNTs, extraordinary extensibility is mainly contributed by buckling and nanohinge-like deformation with maintaining the inner coil diameter. On the other hand, for large CCNTs, this is accomplished by the creation of a straight CNT-like structure in the inner-edge of the CCNT with a helical graphene ribbon twisted around it. Our work represents an important advance in the design of CCNT based mechanical nanodevices.