Nanotube-chirality-controlled tensile characteristics in coiled carbon metastructures

Helically coiled metastructures made from carbon nanotubes (CNTs) are a promising material for nanoelectromechanical systems due to the helical morphology and fantastic properties of CNTs. Mechanical properties of coiled CNT-metastructures are subtly tailored by changing the geometrical parameters; however, the role of CNT-chirality on their mechanical performances remains unknown. Here, using atomistic simulations, stretching characteristics of helical coiled CNTs (HCCNTs) having six different CNT-chirality are contrasted. High initial stiffness of HCCNTs comes from stretching of intercoil van der Waals (vdW) forces while low initial stiffness is explained by sliding action between coils. HCCNTs show distinct characteristic sawtooth patterns in the stretching stress-strain curves, originating from vdW-induced phase transformations, buckling instability and nanohinge-like plasticity. The sawtooth behavior resulting from phase transformations is described by a theoretical model. HCCNTs are highly resilient, and exhibit excellent stretchability because of two distinct deformation mechanisms depending on the CNT-chirality. For HCCNTs composed of armchair and zigzag CNT-segments, extraordinary extensibility is mainly contributed by well-distributed nanohinge-like plastic deformation, whereas for those consisting of other chiral ones this is accomplished by superelasticity and nanohinge-like fracture mechanisms. The findings shed new light in mechanical design of coiled-CNTs for practical applications in nanodevices in coupling to their other properties.