Fang Hongling, Li Yi, Zhang Songwei, Ding Qi, Hu Litian, Lu Kuan
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China; Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100039, PR China.
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China; Qingdao Center of Resource Chemistry & New Materials, Qingdao 266071, PR China.
J Colloid Interface Sci. 2022 Oct;623:257-266. doi: 10.1016/j.jcis.2022.04.174. Epub 2022 May 4.
Ionic liquids (ILs), as lubricant additives, can greatly improve the lubricating behavior of the frictional interfaces. However, it is urgent to explore ILs with good oil solubility in nonpolar oils, and it is necessary to further study and verify the lubrication mechanism of ILs from the perspective of alkyl chain length.
Five protic ILs (PILs) with varying alkyl chain lengths were synthesized by proton transfer method. As additives in PAO oil, their tribological properties were investigated on SRV-V tester. Through molecular dynamics simulation, the adsorption behavior of PILs at the frictional interface was illustrated.
The tribological properties of base oil could be significantly improved by adding PIL additives, but interestingly, PILs with short-chain anions showed better lubricating performance, which contradicted most of the early findings. Further analyses revealed that PILs achieved effective lubrication by the tribochemical interaction between anions and frictional interface, and the formation of cationic protective layer. However, PILs with shorter-chain anions form a denser protective layer that can better support the interfacial anions to participate in tribochemical reactions and thus abnormally exhibit superior lubricating performance than those with longer-chain anions.
离子液体（ILs）作为润滑剂添加剂，能够极大地改善摩擦界面的润滑性能。然而，迫切需要探索在非极性油中具有良好油溶性的离子液体，并且有必要从烷基链长度的角度进一步研究和验证离子液体的润滑机制。
通过质子转移法合成了五种具有不同烷基链长度的质子化离子液体（PILs）。作为PAO油中的添加剂，在SRV-V试验机上研究了它们的摩擦学性能。通过分子动力学模拟，阐明了PILs在摩擦界面的吸附行为。
添加PIL添加剂可显著改善基础油的摩擦学性能，但有趣的是，具有短链阴离子的PILs表现出更好的润滑性能，这与大多数早期研究结果相矛盾。进一步分析表明，PILs通过阴离子与摩擦界面之间的摩擦化学反应以及阳离子保护层的形成实现有效润滑。然而，具有较短链阴离子的PILs形成更致密的保护层，能够更好地支持界面阴离子参与摩擦化学反应，因此反常地表现出比具有较长链阴离子的PILs更优异的润滑性能。
