Five tetrabutylammonium-based amino acid ionic liquids (AAILs), tetrabutylammonium serine ([N 4444 ][Ser]), tetrabutylammonium threonine ([N 4444 ][Thr]), tetrabutylammonium valine ([N 4444 ][Val]), tetrabutylammonium leucine ([N 4444 ][Leu]) and tetrabutylammonium lysine ([N 4444 ][Lys]) have been easily prepared by the neutralization of tetrabutylammonium hydroxide ([N 4444 ][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 byproducts 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 tetrafluoroboratewere 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 [C 6 mim][NTf 2 ] 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.

The present paper investigates a new type of thermoreversible gel lubricant obtained by supramolecular assembly of low-molecular-weight organic gelator (LMWG) in different base oils. The LMWG is a nonionic surfactant with polar headgroup and hydrophobic tail that can self-assemble through collective noncovalent intermolecular interactions (H-bonding, hydrophobic interaction) to form fibrous structures and trap base oils (mineral oils, synthetic oils, and water) in the as-formed cavities. The gel lubricants are fully thermoreversible upon heating-up and cooling down and exhibit thixotropic characteristics. This makes them semisolid lubricants, but they behave like oils. The tribological test results disclosed that the LMWG could also effectively reduce friction and wear of sliding pairs compared with base oils without gelator. It is expected that when being used in oil-lubricated components, such as gear, rolling bearing, and so on, gel lubricant may effectively avoid base oil leak and evaporation loss and so is a benefit to operation and lubrication failure for a long time.