Role of humidity in reducing the friction of graphene layers on textured surfaces

Abstract

A multiple-layer graphene was prepared on steel surface to reduce friction and wear. A graphene-containing ethanol solution was dripped on the steel surface, and several layers of graphene flakes were deposited on the surface after ethanol evaporated. Tribological performance of graphene-contained surface (GCS) was induced by reciprocating ball against plate contact in different RH (0% (dry nitrogen), 30%, 60%, and 90%). Morphology and wear scar were analyzed by OM, 2D profile, SEM, Raman spectroscopy, and XPS. Results show that GCS can substantially reduce the wear and coefficient of friction (COF) in 60% relative humidity (RH). Low COF occurs due to graphene layer providing a small shear stress on the friction interface. Meanwhile, conditions of high RH and textured surface could make the low COF persist for a longer time. High moisture content can stabilize and protect the graphene C-network from damage due to water dissociative chemisorption with carbon dangling bonds, and the textured surface was attributed to release graphene layer stored in the dimple.

Effect of Humidity on Friction and Wear—A Critical Review

“…humidity increases [26][27][28]. As shown in Figure 1, the phenomenon was attributed to the dissociative chemisorption of water at carbon dangling bond sites exposed upon rupture of graphene.…”

“…Graphene shows great lubricity as a coating material [24][25][26]. Similar to graphite, when the graphene coating is rubbed with a macroscale counterpart, the friction and wear decreases as the environmental humidity increases [26][27][28]. As shown in Figure 1, the phenomenon was attributed to the dissociative chemisorption of water at carbon dangling bond sites exposed upon rupture of graphene.…”

Effect of Compressive Prestrain on the Anti-Pressure and Anti-Wear Performance of Monolayer MoS2: A Molecular Dynamics Study

“…Both atomic force microscopy (AFM) experiments [4,13] and molecular dynamics (MD) simulation [14,15] have indicated that MoS 2 shows an excellent mechanical property, with the effective Young's modulus of 270 ± 100 GPa and the average breaking strength of about 23 GPa [4]. Macroscopic friction experiments indicate that MoS 2 possesses an excellent lubrication property [16] even in vacuum [17][18][19], while graphene shows a poor lubrication property in dry conditions [20][21][22]. It indicates that MoS 2 is an ideal substitute material for graphene in terms of environmental sensitivity.…”

Toward Robust Macroscale Superlubricity on Engineering Steel Substrate

“…[9][10][11][12][13] It is essential that an ideally rigid layerby-layer sliding structure with weak interaction remains atomically flat, molecularly clean, and structurally incommensurate so as to achieve structural superlubricity. [3,7,14] In a macroscopic sense, however, surface asperities have physical interlocking actions and thus affect the friction; and there inevitably are disordered structure, defect, chemical interaction, [15] adsorption, [16] and friction-induced damage [17] during the rubbing process of macroscale contact. In particular, there is often a large contact area at sliding interface and there are countless macroscale asperities on the contact surface, which makes it impracticable to maintain large-area incommensurate contact.…”

“…This indicates that air atmosphere with a certain activity is beneficial to the self-orientation of the graphene/MoS 2 composite during pre-running-in period. In other words, the active molecules of oxygen and H 2 O in air could passivate the defects and edge bonds of the nanosheets of graphene/MoS 2 composite, [16,17,25] and the nanocomposite allows its nanosheets to sprawl along substrate surface, thereby forming an ordered layer-by-layer structure owing to their unique thin-paper structure. During pre-running-in in inert nitrogen atmosphere, however, the interactions among the defects or edge bonds of the adjacent layers of the nanocomposite become dominant, which leads to severe damage to the original structure of the nanosheets and disturbs their self-orientation.…”