Effects of Thickness and Particle Size on Tribological Properties of Graphene as Lubricant Additive

Abstract

Increasing studies have demonstrated excellent tribological properties of graphene as lubricant additive. Thus, extended explanations of the relationship between microstructure and tribological properties are needed. This paper reported the effects of thickness and particle size of graphene on its frictional performance, using a ball-on-plate tribotester under reciprocating condition. Graphene with few-layer (G2) or multi-layer (G10) structure was added to PAO4 as lubricant additive. The particle of G10 was further separated through centrifugation into two types, large size G10 (G10L) and small size G10 (G10S). G10S exhibits excellent reduction in friction (37%) and wear (47%) relative to the neat base oil, indicating the superior tribological properties of graphene with more layers and smaller particle size. Wear scar analysis shows that the surface lubricated with G10 is flatter and glossier than that of G2. It can be hypothesized that the interlaminar shear slip is more likely to occur in multi-layer graphene, leading to better friction reduction and wear resistance performance. Graphene with smaller particle size is not only less prone to structural defects and wrinkles, but also more easily adsorbed onto the sliding surface to form a lubricating film, providing enhanced wear and frictional performance. The present work suggests that the thickness and size may have direct influence on the tribological properties of graphene, providing theoretical and experimental guidance for the application of graphene as lubricant additive.