Five tetrabutylammonium-based amino acid ionic liquids (AAILs), tetrabutylammonium serine ([N4444][Ser]), tetrabutylammonium threonine ([N4444][Thr]), tetrabutylammonium valine ([N4444][Val]), tetrabutylammonium leucine ([N4444][Leu]) and tetrabutylammonium lysine ([N4444][Lys]) have been easily prepared by the neutralization of tetrabutylammonium hydroxide ([N4444][OH]) with the five corresponding amino acids. These AAILs only contain the elements C, N, O and H in their structures, so they are more environmentally friendly than conventional phosphorus-, halogen- or sulfur-containing lubricants. The preparation process of these AAILs is simple and also fully green, because no other by-products except water were produced during the whole process. The AAILs were evaluated as green lubricants for various surface contacts, such as steel/steel, steel/copper and steel/aluminum, using an Optimol SRV-IV oscillating reciprocating friction and wear tester at room temperature (RT). Due to their halogen-free character, these AAILs have a higher hydrolysis stability and a far lower corrosion level than the halogen-containing lubricants imidazolium ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C6mim][NTf2]), which were also tested. The tribotest results revealed that these AAILs could act as lubricants to effectively reduce friction and wear of all sliding pairs, and they even showed superior tribological performances compared to poly-alpha-olefin (PAO40) and [C6mim][NTf2] under the experimental conditions. The worn surfaces of the lower discs were analyzed by X-ray photoelectron spectrometry (XPS). Based on the XPS results, it can be concluded that the good lubricating properties of the AAILs are attributed to the formation of physically adsorbed layers on the metal surfaces during the rubbing process.
四丁基
铵丝氨酸([N4444][Ser])、四丁基
铵苏
氨酸([N4444][Thr])、四丁基
铵缬
氨酸([N4444][Val四丁基
铵亮
氨酸([N4444][Leu])和四丁基
铵赖
氨酸([N4444][Lys])是通过
氢氧化四丁基铵([N4444][OH])与五种相应的
氨基酸中和而容易制备的。这些
AAIL 的结构中只含有 C、N、O 和 H 元素,因此比传统的含
磷、卤素或
硫润滑剂更环保。这些
AAIL 的制备过程非常简单,而且完全绿色环保,因为在整个过程中除了
水之外不会产生其他副产品。使用 Optimol SRV-IV 摆动往复式摩擦和磨损测试仪在室温 (RT) 下对
AAIL 作为绿色润滑剂用于钢/钢、钢/
铜和钢/铝等各种表面接触进行了评估。由于不含卤素,这些
AAIL 具有更高的
水解稳定性,腐蚀程度也远远低于含卤素的润滑剂
咪唑鎓 IL(1-丁基-3-甲基
咪唑鎓四
氟硼酸盐([C4mim][BF4])和 1-己基-3-甲基
咪唑鎓双(三
氟甲基磺酰基)
亚胺([C6mim][NTf2])。摩擦试验结果表明,这些
AAIL 可用作润滑剂,有效降低所有滑动对的摩擦和磨损,在实验条件下,它们的摩擦学性能甚至优于聚α-烯烃(PAO40)和 [C6mim][NTf2]。通过 X 射线光电子能谱(XPS)分析了下圆盘的磨损表面。根据 XPS 结果,可以得出结论:
AAIL 的良好润滑性能归因于摩擦过程中在
金属表面形成的物理吸附层。