Tribological properties of amidoxime-based protic ionic liquids as lubricant additives for PAO10

Protic ionic liquids (PILs) have been emphasized in recent years owing to their convenient synthesis routines and outstanding lubricity properties. In this work, amidoxime-based PILs were investigated as additives in PAO10. The tribological tests demonstrated that these newly synthesized PILs could highly improve the friction-reducing, anti-wear, variable-frequency and load-carrying capacity properties of PAO10. The results of contact angle, ECR, SEM-EDS and XPS analysis revealed that the tribofilm consisted of a physical absorption layer containing organic carbonaceous species and a tribochemical film containing Fe 2 O 3 , which is responsible for the significant improvement of tribological performances of PAO10. • Cation-functionalized amidoxime-based PILs used as lubricant additives in POA10. • PAO10 with 1 % amidoxime-based PILs maximally reduces friction by 63 % and wear by 93 %. • Electrostatic/coordination/tribochemical effects jointly generate the tribofilm.