Fortified Lubricating Response to Sustainable PEG System from Protic Ionic Liquid and Their Strong Hydrogen Bonding Network

As a hydrophilic polyether molecule, polyethylene glycol has environmentally friendly, degradable, and compatibility characteristics, gradually becoming a potential choice for green lubrication. Two novel multifunctional protic ionic liquids (ILs) were synthesized, and an ILs-PEG200 lubrication system was constructed with a strong hydrogen bonding network structure. The determination of rheological properties and boundary lubrication states inspired us to consider the interaction between polar additives and systems. Surprisingly, an extremely stable run-in period was obtained by the high efficiency adsorption contributed from high-polarity ILs at the sliding interface in the initial shear stage. Meanwhile, the ILs-PEG200 lubrication system also has superior load carrying and antishear properties, as well as remarkable lubrication stability even under very high loads, showing certain potential for engineering applications. In addition, the lubrication mechanism was obtained by exploring the interaction among ILs, PEG system, and metal surface, and the results revealed that tribo-oxidation reactions, physical/chemical adsorption, and tribochemical reactions occurred on the metal asperity during shear. Therefore, a tribofilm containing metal phosphates and sulfides is generated through the occurrence of tribochemical reaction and the synergistic effect of the base system, metal interface, and functional additives. The protic ILs lubrication additives in this work can significantly enhance the tribological performance of poly(ethylene glycol) systems under harsh conditions, providing a theoretical basis for its development in the engineering field.