ZnO nanoparticles coated with oleic acid as additives for a polyalphaolefin lubricant

•Oleic acid coated ZnO NPs of 10 nm diameter were synthetized and characterized.•PAO40 + 0.25 wt% ZnO-OA dispersion led reductions of 25% in friction and 82% in wear.•Last dispersion shows time stability up to 29 days.•Roughness reductions in the worn surface reach 43% using the optimized nanolubricant.•Raman microscopy revealed protective tribofilms on the wear tracks composed by PAO40, ZnO-OA NPs and iron oxides.