rGO/GO Nanosheets in Tribology: From the State of the Art to the Future Prospective

Abstract

In the last few decades, in the lubricant industry, the request for new performing additives has been becoming imperative. In this scenario, control at the nanoscale can be the key factor for the improvement of more efficient nanolubricants. Herein, after a discussion about the nanoparticles’ four main lubrication mechanisms, considerable attention is devoted to the usage of reduced graphene oxide/graphene oxide (rGO/GO) nanosheets in tribology. Moreover, graphene surface functionalization is reviewed, also including unexplored results in the field of lubrication. As far as the literature is concerned, it can be postulated that rGO/GO nanosheets can reduce wear and friction. Wear reduction is obtained by deposition and film formation, while friction reduction is related more to the shear and lamination of the sheets on the contacting surfaces. Nevertheless, the two phenomena are interrelated and work in sync. In this context, it is of high importance to form a homogenous suspension for a continuous nanosheet supply after deposition and shearing. The focus of this review was placed on the main issues still to be overcome, e.g., the literature results in rationalization; dispersion stability enhancement; and finding the optimum concentration in the delicate balance of different components. Possible solutions for their efficient overcoming are eventually reported.

Recent Advances in Preparation and Testing Methods of Engine-Based Nanolubricants: A State-of-the-Art Review

“…Furthermore, graphene and its oxide derivatives, such as graphene oxide GO and reduced graphene oxide rGO, showed a superb tribological and heat transfer performance, as mentioned in many studies [62,63,65,111,172]. This returns to the multi-layer nature of this family of nano additives that are easily sheared, due to its high chemical stability and weak van der Waals forces between its sheets [64,172]. These characteristics of graphene and its constituents make them a worthy preference as a lubricant additive.…”

“…On top of that, GO and rGO possess better mechanical and thermal conductivity properties and dispersion stability than pure Gr [172].…”

“…Besides their tribological and rheological features, some other attributes should be taken into account. This includes their size, surface morphology, and the internal structure of the nanoparticles, which is determined by the quality and processing of these nano constituents [172,174]. The size of the nanoparticles defines their internal physicochemical and mechanical properties, altering their tribological properties.…”

Investigating Physio-Thermo-Mechanical Properties of Polyurethane and Thermoplastics Nanocomposite in Various Applications

“…Chemical reduction is an effective method of obtaining reduced graphene oxide (RGO) which can be dispersed in aqueous or solvent media and solve the disruption of sp2 carbon structure [111]. Nevertheless, GO tends to aggregate and re-stack due to large van der Waals forces as well as π-π interactions [112]. Compatibilization of graphene via non-covalent and/or covalent interactions is an effective way to enhance surface adhesion with the polymer matrix and prevent aggregation.…”

A Comprehensive Review of Water-Based Nanolubricants

“…Generally, spherical NPs reduce the COF by converting sliding friction to rolling friction as a result of their morphological properties [233][234][235]. Some scholars have revealed that these NPs themselves might roll or embed into surfaces [236][237][238]. Moreover, many scholars have mentioned the ball bearing effect in lubrication mechanism analysis of the water-based nanoadditives including metal and non-metal oxide [54,59,100], composite [86,119], and many more [68,78,92,124,137,159].…”