Magnetic fluids (MFs) represent a unique class of smart functional lubricating material, with their physical properties tunable by the application of a magnetic field. In this study, stable MFs were prepared at varying mass fractions of Fe₃O₄ nanoparticles. The influence of magnetic field on their tribological behaviors was examined on a modified rotational rheometer in both boundary and mixed lubrication regimes. The results show that the magnetic field significantly enhance the tribological performance of the MFs, especially for boundary lubrication. In particular for the MF containing 1wt% Fe₃O₄ nanoparticles, a friction reduction of 41.2% and a wear volume reduction of 94.7% were achieved in the presence of magnetic field. Post-analysis of the worn surfaces was carried out with multiple techniques to gain deeper insights into the lubrication mechanisms. In boundary lubrication regime, the magnetic field aids in introducing a larger amount of Fe₃O₄ nanoparticles into the contact, leading to the formation of a more continuous deposit film.

An oil soluble multifunctional protic ionic liquid (IL) was synthesized and its tribological and antioxidant properties in poly alpha olefin (PAO4) were investigated. The tribological results demonstrated that the IL significantly reduced friction and wear of PAO4. The PAO4 blend with IL resulted in an induced oxidation time of 555 min which is 8.2 and 3.5 times higher than that of pure PAO4 and PAO4 with zinc dialkyl dithiophosphate (ZDDP) for the rotating pressure vessel oxidation test. It is likely that free nonylated diphenylamine acted as a radical scavenger to enhance antioxidant performance, while free bis(2-ethylhexyl) phosphate was more prone to adsorb and react with the metal surface to form a phosphorus-rich tribofilm in order to protect the rubbing surface.

Unlike most of the conventional ionic liquids (ILs) derived from non-renewable resources, five environmentally friendly ILs ([Ch][AA] ILs) derived from amino acids (AAs) and choline (Ch) were synthesized using biomaterials by a simple, green route: acid–base reaction of Ch and AAs. The thermal and corrosion properties, as well as viscosity, of the prepared ILs were examined. The results revealed that the anion structure of ILs plays a dominant role in their thermal and viscosity behavior. These ILs exhibited less corrosion toward copper, related to their halogen-, sulfur-, and phosphorus-free characteristics. The tribological behavior of the synthesized ILs was examined using a Schwingungs Reibung und Verschleiss tester, and the results indicated that these ILs exhibit good friction-reducing and anti-wear properties as lubricants for steel/steel contact. Results from energy-dispersive spectroscopy and X-ray photoelectron spectroscopy indicated that the good tribological properties of [Ch][AA] ILs are related to the formation of a physically adsorbed film on the metal surface during friction.