Understanding the Physical Adsorption Action Mechanism of MoS₂ Nanoparticles in Boundary Lubrication with Different Polyisobutyleneamine Succinimide (PIBS) Concentrations

The lubrication mechanism of nanoinorganic particles during friction process has been widely investigated. However, the physical adsorption action mechanism between the nanoparticles (after modification) and friction pairs has so far never been studied in detail. In this study, the various concentrations of polyisobutyleneamine succinimide (PIBS) by weight in paraffin oil were applied to study their effect on the tribological behaviors of nano-MoS₂ oil. And the tribological results were further discussed to understand the lubricating action mechanism of nano-MoS₂ particles additive. The results show that the tribological behavior of modified nanoparticles was significantly influenced by PIBS concentration. The COF reduced from 0.139 to 0.090 with low PIBS concentration (less than 0.1 wt%), while the COF reduced to 0.126 with higher PIBS concentration (more than 0.2 wt%). By scanning electron microscopic (SEM) and energy-dispersive X-ray spectroscopy, some mechanisms likely related to this interesting results are revealed. It is identified that: (1) production of MoS₂ tribofilm on steel surface reduces the COF and wear, (2) wear scar is smooth with low PIBS concentration, while it shows plowing wear with high PIBS concentration, (3) the MoS₂ tribofilm is found by SEM on the wear scar of the nano oil with 0.05 wt% PIBS. A three-step lubricating action mechanism of the modified nano-MoS₂ particles has been proposed as an explanation for the interesting results. The results indicate that physical adsorption provide an initial action for nanoparticle lubricant to form tribofilm in boundary lubrication.