Dynamic Sliding Enhancement on the Friction and Adhesion of Graphene, Graphene Oxide, and Fluorinated Graphene

Abstract

Graphene and functionalized graphene are promising candidates as ultrathin solid lubricants for dealing with the adhesion and friction in micro- and nanoelectromechanical systems (MEMS and NEMS). Here, the dynamic friction and adhesion characteristics of pristine graphene (PG), graphene oxide (GO), and fluorinated graphene (FG) were comparatively studied using atomic force microscopy (AFM). The friction as a function of load shows nonlinear characteristic on GO with strong adhesion and linear characteristic on PG and FG with relatively weak adhesions. An adhesion enhancement phenomenon that the slide-off force after dynamic friction sliding is larger than the pull-off force is observed. The degree of adhesion enhancement increases with the increasing surface energy, accompanied by a corresponding increase in transient friction strengthening effect. The dynamic adhesion and friction enhancements are attributed to the coupling of dynamic tip sliding and surface hydrophilic properties. The atomic-scale stick-slip behaviors confirm that the interfacial interaction is enhanced during dynamic sliding, and the enhancing degree depends on the surface hydrophilic properties. These findings demonstrate the adhesive strength between the contact surfaces can be enhanced in the dynamic friction process, which needs careful attention in the interface design of MEMS and NEMS.

Dependence of the fluorination intercalation of graphene toward high-quality fluorinated graphene formation

“…There is no doubt that the interlayer distance is a crucial structural factor to regulate the excellent performances of 2D materials. For example, fluorinated graphene has been supposed to become an advanced lubricant, because effective fluorination intercalation decreases the interlayer surface energy and simultaneously increases the interlayer distance, thus improving its self-lubricating ability 13,39. Its self-lubricating ability, determined by the interlayer van der Waals attraction energy ( E vdW ), can be calculated by E vdW = – d 0 4 γ / h 4 , where d 0 = 0.335 nm, γ is the surface energy and h is the interlayer distance 31,40.…”

Quantification/mechanism of interfacial interaction modulated by electric potential in aqueous salt solution

“…These hydroxyl groups partake in hydrogen bonding with the hydroxyl groups on the SiO 2 microsphere, leading to high adhesion [27,40,41,63]. Adhesion plays an important role in nanoscale friction, with friction generally increasing with adhesion forces [64,65]. Nanoscale friction is linearly correlated with load for weak adhesion between two surfaces [66,67].…”

Thickness and Structure of Adsorbed Water Layer and Effects on Adhesion and Friction at Nanoasperity Contact

“…Water adsorption can also significantly alter the friction behaviors on 2D material surfaces. Graphene surfaces are well known to provide extreme low friction due to their low surface energy [129][130][131]. However, F t increases substantially when the graphene surface is oxidized ( Figure 19) [126].…”