Synthesis, characterization and tribological evaluation of novel 1,4-diazabicyclo[2.2.2]octane based dicationic ionic liquids as efficient antiwear lubricant additives

Ionic liquids have developed and been applied in lubricant field since 2001. Nevertheless, it is little known about novel dicationic ionic liquids for tribology applications in the past several years. In this paper, a sequence of novel dicationic ionic liquids based on 1,4-diazabicyclo[2.2.2]octane cations (DABCO) and different anions have been designed and identified. The structures of ILs were confirmed by Fourier transform infrared (FTIR) spectra, multinuclear (1H, 13C, 11B, 31P and 19F) magnetic resonance and mass spectrometry. The effects of anion type on thermal properties, wettability, kinematic viscosity and tribological properties were studied. It is found that all of these dicationic ionic liquids as additives exhibit excellent anti-wear and friction-reducing properties in PEG synthetic base oil under boundary lubrication conditions for steel-to-steel contact, which offers great potential for the highly efficient lubricant additives. Simultaneously, novel 1,4-diazabicyclo[2.2.2]octane cation offers an exceptional chance for the research and development of dicationic ionic liquids in various applications.