The effect of non-uniform pitch length and spiraling pathway on the mechanical properties of coiled carbon nanotubes

Abstract

Coiled carbon nanotubes (CCNTs) exhibit exceptional mechanical, electrical, and thermal properties, making them suitable for diverse applications such as nanoelectromechanical devices. Here, classic molecular dynamics (MD) simulations were employed to investigate the coil morphology and the uniaxial tensile characteristics of thirteen CCNTs that were constructed by twisting carbon nanotube (CNT) segments of toroid formed by six identical CNT segments, with intricate effects of coil spacing and twist-induced spiraling pathway. The MD results showed that the coil morphology and stretching properties of CCNTs are greatly dictated by pitch length and spiraling pathway. All CCNTs showed unique characteristics of sawtooth-like patterns in the tensile stress-strain curves, originating from the separation of van der Waals (vdW) attracted coils, strain-induced buckling of CNT segments and nanohinge-like plastic deformations. Depending on the non-uniform pitch length and spiraling pathway of twisted CCNT segments, CCNTs exhibit different mechanical properties including Young's modulus, elastic limit, tensile strength, fracture strain, stiffness coefficient and distinguishing deformation mechanisms. Particularly, the fracture strain and tensile strength are significantly dictated by the pitch length and spiraling pathway, respectively. The elastic proprieties of finite element (FE) models scaled to CCNTs were established for comparison with the case of CCNTs with symmetrical spiraling. Moreover, CCNTs show high toughness that can be controlled by the pitch length and spiraling pathway. This study provides new insights and perspectives into the mechanical properties of nanocoils, which is of help to designing optimal nanocoils for nano-device systems.