Atomistic mechanisms of superlubricity in carbon nanotube heterostructures under linear elastic deformation

Abstract

Heterostructures have been introduced to achieve superior performance by assembling low-dimensional van der Waals materials. However, the friction properties of nanohybrids composed of one-dimensional (1D) nanotubes and two-dimensional (2D) materials remain challenging to detect experimentally. Herein, we employ atomic simulations to investigate the relationship between friction and deformation in a sandwich structure, where a single-walled carbon nanotube (SWCNT) is encapsulated between graphene layers. The results demonstrate that the nanotube shape transitions from a circular to oval cross section, and eventually collapses as compressive force increases. In the linear elastic regime, the radial stiffness of SWCNT exhibits an inverse cubic dependence on the nanotube radius (K ∝ 1/R³). Concurrently, the rolling ratio in the linear elastic deformation regime is described by a cubic equation. As the nanotubes are squeezed into collapsed states, the motion changes from rolling to sliding. The transition of movement is attributed to the competition between strain energy and adhesion energy. The shear stress remains nearly constant during rolling, while it increases proportionally with normal stress under sliding conditions. Our findings provide deep insights into the linear elastic properties of nanotubes, contributing to their potential applications in reinforced composite materials and the design of rolling superlubricity for nano-electro-mechanical system (NEMS) devices.