Synergistic lubrication effect of graphene oxide and MoS2 nanoparticles in water-based fluid: Experiment and humid-environmental MD simulation study

In this study, a lubricant was synthesized using water-based hybrid nanofluid containing graphene oxide (GO) and MoS₂ nanoparticles. Pin-on-disk tribology tests and molecular dynamics (MD) simulations under humid environment were conducted. It was discovered that the GO-MoS₂ hybrid nanofluid, at the optimal concentration combination (0.3 wt% GO + 0.1 wt% MoS₂), demonstrated a notably enhanced synergistic lubrication effect, resulting in a reduction of approximately 14.6 % in the average friction coefficient and 14.4 % in the wear rate when compared to the single nanofluid. Through interfacial tribochemical analysis, a protective polycrystalline tribofilm in the thickness of about 18.6 nm was formed on metal surface, consisting of ultra-fine GO, MoS₂ crystals and amorphous substances derived from the organic matters of nanofluids. Besides, from humid-environmental MD simulation results, there were lower friction force, normal force and peak temperature values in MD model containing both GO and MoS₂ nanosheets, meanwhile the lattice mismatch between different nanosheets led to high interlamellar repulsion, further mitigating the pressure and friction. By analyzing the absorption behavior of dispersant molecules, sodium dodecylbenzene sulfonate and triethanolamine molecules partially transferred from nanosheets to Fe surface. Based on the experiment and humid-environmental MD simulation results, the excellent tribological behavior of nanofluid was attributed to the polishing, mending, interlayer sliding effect of nanoparticles and the tribofilm induced by interfacial tribochemistry.