Super lubricity of grapheme oxide achieved by development of transfer films in nitrogenenvironment

摘要

Graphene and graphene oxide (GO) are emerging solid lubricants that have been investigated for sliding applications in various environments [1]. The majority of these works investigate graphene (and related materials) as additives in conventional liquid lubricants. But, few recent solid lubrication studies have demonstrated that solvent-casting few-layer graphene onto 440C stainless steel can result in a reduction in the coefficient of friction (COF) from ～1.0 to ～0.2, and an increase in wear lifetime by more than three orders of magnitude (air, 30% RH) [2, 3]. However, superlubricity has been observed for graphene sliding against a diamondlike carbon (DLC) counterface (COF ～0.004) [4]. This was attributed to the formation of nanoscrolls which reduce the contact area between the surfaces. In a recent study, we investigated the interesting tribological behavior of polyethylenimine / graphene oxide (PEI/GO)n LbL solid lubricant coatings in air, vacuum, nitrogen, and hydrogen gas environments [5]. Extraordinarily super low COFs (～0.02) and long wear lifetimes were reported, depending on environment [5]. However, here we present a separate investigation of particular focus on transfer film with six different polymer counterface balls and microstructural characterization of those transfer films to gain insight into the mechanism behind these significant improvements.