Environmental Molecular Effect on the Macroscale Friction Behaviors of Graphene

Abstract

This study investigated the friction behavior of graphene in air and nitrogen atmosphere environments. The microstructural evolution caused by the variation of atmosphere environments and its effect on the friction coefficient of the graphene is explored. It is demonstrated that graphene can exhibit excellent lubricating properties both in air and nitrogen atmosphere environments. In air, a highly ordered layer-by-layer slip structure can be formed at the sliding interface. Oxygen and H2O molecules can make edge dangling bonds and defects passive. Thus the interaction between the nanosheets and the layers of nanosheets is weak and the friction coefficient is low (0.06–0.07). While the friction coefficient increases to 0.14–0.15 in a nitrogen atmosphere due to the interaction of defects generated in the sliding process, the nitrogen molecules with lone pair electrons can only make the nanosheets passive to a certain degree, thus the ordered slip structure is destroyed and friction is higher. This work reveals the influence of environmental molecules on the macroscale tribological performances of graphene and its effect on the microstructure at the sliding interface, which could shed light on the lubricating performance of graphene in environmental atmospheres and help us to understand the tribological behaviors of graphite at the macroscale.

Study on current-carrying tribological characteristics of C-Cu sliding electric contacts under water accumulation from rainfall condition

“…Sukanta found that a relative humidity of 45% will cause graphene to establish a transfer layer on the contact surface, H+ and OH− ions will blunt the surface of graphene, thereby reducing friction [21]. Li found that water molecules can enter graphene interlayers and passivate defects and edge dangling bonds, resulting in weakened interlayer interactions and reduced friction coefficient [22]. Allouche found that water on the surface of layered graphite adsorption terminated the active edge bonds of graphite, thereby reducing the surface energy of graphite and improving its self-lubricating performance [23].…”

A Generalised Method for Friction Optimisation of Surface Textured Seals by Machine Learning

“…On the one hand, material properties, such as the crystal structure [3], hardness [4,5], elastic and shear modulus [6,7], grain size [8,9], and surface energy [10,11] of the contacting materials affect the frictional behaviour. On the other hand, the operational conditions, such as the normal loads [12,13], sliding velocities [14,15], environmental conditions [16,17], temperatures [18], and lubricants [19], have a major influence on the tribological behaviour. Of particular relevance are surface coatings or modifications of the surface topographies [20], which both can contribute significantly to the friction behaviour.…”

Influence of Interfacial Chemistry and Oxygen on Graphene Step Edges as Antiwear Coatings

“…Two-dimensional materials such as graphene have been extensively employed as antiwear coatings at microscale due to their ultrahigh in-plane mechanical strength and ultralow interlaminar shear strength. − However, their excellent tribological performance is normally difficult to be directly extended at macroscale due to abundance of defects involving atomic step edges inevitably existing in the deposited coating, which are sensitive to wear depending on the experimental atmosphere. − Therefore, understanding the contributions of molecules in surrounding air to the wear of graphene step edge (a typical defect) is essential to optimizing the antiwear coating at any length scale.…”