Tribological improvement of potential lubricants for electric vehicles using double functionalized graphene oxide as additives

The aim of the present research is to analyze thermophysical and tribological properties of PAO4 nanolubricants containing functionalized (GO-polyethyleneimine-oleic acid, GO-PEI-OA) and non-functionalized (GO) graphene oxide. Nanodispersions of these NPs were prepared, observing a better stability for the GO-PEI-OA nanolubricants. As for the tribological properties, significant improvements in coefficient of friction were obtained comparing with the base oil, being 28% for GO-PEI-OA (0.10 wt%). Concerning the anti-wear behavior, better results were obtained for GO-PEI-OA nanolubricants (0.15 wt%) with improvements of about 27%, 54% and 60% for the diameter, depth, and area of the wear track, respectively. Finally, Raman spectroscopy and surface roughness measurements were used to identify the tribological mechanisms of tribofilm formation and repairing.