Tribological Performance of Raft‐Modified Graphene Oxide as a Lubricant Additive

ABSTRACT This study investigates the tribological performance of graphene oxide (GO) grafted via reversible addition–fragmentation chain transfer (RAFT) polymerization with two methacrylate monomers: 2‐hydroxyethyl methacrylate (HEMA) and pentyl pentanoate methacrylate (PPEMA). Extensive analyses—including Fourier‐transform infrared spectroscopy (FTIR), Raman spectroscopy, X‐ray diffraction (XRD), solid‐state nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectroscopy (EDS)—confirmed successful polymer grafting onto GO surfaces. Adding 0.5 wt% of these grafted GO additives to castor oil significantly reduced friction and wear compared to neat oil and pristine GO dispersions. Graphene oxide grafted with PPEMA (GO–PPEMA) achieved the lowest friction coefficient and more stable sliding behavior, attributed to its hydrophobic side chains forming effective boundary films and reducing shear. Meanwhile, graphene oxide grafted with HEMA (GO–PHEMA) offered slightly better wear protection due to enhanced interfacial interactions from its polar hydroxyl groups. Thermal analyses revealed increased decomposition temperatures for both composites, confirming their stability under frictional heat. Overall, RAFT‐mediated polymer grafting effectively tailors the tribological properties of GO additives, offering a promising strategy for advanced and sustainable lubrication systems.