Structure engineering-driven sustainable ionic liquid water-based lubricants and their high-efficiency lubricity and antibacterial properties

Achieving high performance and multi-functional synergy at low concentration has always been an urgent pursuit for lubricating additives, which is closely related to its structural regulation and composition optimization. In this work, two kinds of protic ILs (P 6 N 12 and P 6 N 12 O) were synthesized with different molecular structures concerning the presence of carbonyl (-C O) structure. Structurally, the introduction of -C O structure obviously enhances the compatibility and stability with water-based basic system. Not limited the enhanced corrosion resistance, ILs can effectively improve surface wettability and adsorption, resulting from the formation of the protective film on the metal surface. Furthermore, the improvement of friction-reducing (more than 70%) and anti-wear (over 90%) performance is worth noting at the steel/steel tribo-pairs even at the contact stress of 2.72 GPa, which is ascribed to the self-assembly behavior and strong interaction of IL molecule on the sliding asperity. XPS analysis and DFT calculations show that carbonyl group in P 6 N 12 O enhances the electron delocalization and charge transfer at the interface, which promotes the in-situ formation of tribofilm composed of iron oxide and phosphate, resulting in the enhanced stronger adsorption and high-bearing characteristics. The antibacterial rate of two ILs against Staphylococcus aureus reached 99.9%, but the activity of P 6 N 12 O against Escherichia coli was weak, which was due to the conformational change charge distribution and electrostatic attraction with bacterial surface that caused by carbonyl group. The obtained structure-activity relationship in this work provides the theoretical guidance and experimental data reference for the enrichment and development of water-based lubricants.