Mechanical behavior and micro-mechanism of carbon nanotube networks under friction

Friction behavior of carbon nanotube networks (CNNs) is ubiquitous in applications, however, is poorly investigated. Here, we employ coarse-grained molecular dynamics (CGMD) simulations to investigate friction behaviors and microscopic mechanism of CNNs. We first give a phase diagram to determine the initial contacting state of “supported” or “trapped” for an indenter in CNNs. In a “supported” state, friction force is mainly originated from the local surface adhesion of CNNs which experience stable elastic deformation in friction process. In contrast, in a “trapped” state, friction force is mainly activated by nonlocal reconstitution of carbon nanotubes (CNTs) accompanied with irreversible bond breaking. Furthermore, with an increased normal pressure, the friction force keeps nearly constant for a “supported” indenter while it increases linearly for a “trapped” one; the friction force is linearly or nonlinearly related to the sliding velocity of an indenter in a supported or trapped state. Importantly, there is a critical crosslink density, above which, the coefficient of friction is greatly decreased due to enhanced integrity of CNNs. These results provide a profound understanding of friction deformation behavior of CNNs, which is of great significance for optimal design in practical applications.