由简单质子型离子液体水溶液中的界面摩擦化学反应所引发的有效超润滑性能

超润滑技术是近年来摩擦学领域中发展最为迅速的分支之一，因为它能够从根本上降低摩擦和磨损。然而，目前液态超润滑所面临的挑战在于润滑剂的承载能力以及在高剪切速率下稳定超润滑状态的能力。在这项研究中，制备了四种不同链长的咪唑磷酸离子液体（ILs），并将其用作纯水添加剂，以在钢界面之间实现稳定的超润滑状态，当载荷为 300 牛、速度为 0.461 米/秒时，摩擦系数仅为 0.008。通过分阶段实验探索了超润滑的演变过程和摩擦化学反应。结果表明，实现超润滑的关键因素是磨合期，在此期间，接触压力大幅降低，以保持合适的承载范围。另一方面，氢离子、有机阴离子和阳离子以及水合离子的有序聚集在摩擦对的界面处形成了多层静电层，这不仅为避免严重的腐蚀提供了一层保护层，而且由于静电排斥作用还增强了润滑膜的承载能力。此外，离子液体与金属表面之间的摩擦化学反应形成了由碳化物、氧化铁、氮化物和磷化物组成的功能性摩擦膜，这种膜防止了摩擦对的直接接触并减少了磨损。因此，这项研究为优化离子液体结构提供了有价值的见解，揭示了超润滑过程中的摩擦化学反应，并展示了水基超润滑系统在实际应用中的巨大潜力。Ultra-low friction (superlubricity) technology is one of the fastest-growing branches in the field of tribology in recent years, as it can fundamentally reduce friction and wear. However, current challenges for liquid-based superlubricity lie in the load-bearing capacity of lubricants and their ability to maintain a stable superlubricity state under high shear rates. In this study, four imidazolium phosphate ionic liquids (ILs) with different chain lengths were synthesized and used as additives to pure water to achieve a stable superlubricity state between steel interfaces, with a friction coefficient as low as 0.008 under a load of 300 N and a sliding speed of 0.461 m/s. The evolution process of superlubricity and the tribochemical reactions were explored via staged experiments. The results show that the key factor for achieving superlubricity is the running-in period, during which the contact pressure decreases significantly to maintain an appropriate load-bearing range. On the other hand, the ordered aggregation of hydrogen ions, organic anions and cations, as well as hydrated ions, forms a multi-layered electrostatic layer at the interfaces of the friction pairs. This layer not only provides a protective layer to avoid severe corrosion, but also enhances the load-bearing capacity of the lubricating film via electrostatic repulsion. Furthermore, the tribochemical reactions between the ionic liquids and the metal surfaces form a functional tribofilm composed of carbides, iron oxides, nitrides and phosphides. This film prevents direct contact between the friction pairs and reduces wear. Therefore, this study provides valuable insights for the optimization of ionic liquid structures, reveals the tribochemical reactions during the superlubricity process, and demonstrates the great potential of water-based superlubricity systems for practical applications.