Bisimidazolium ionic liquids as the high-performance antiwear additives in poly(ethylene glycol) for steel-steel contacts.

Bisimidazolium ionic liquids [C(10)(m(2)im)(2)(NTf(2))(2), C(10)(m(2)im)(2)(PF(6))(2), and C(10)(m(2)im)(2)(BF(4))(2)] with different anions were evaluated as the antiwear additives in poly(ethylene glycol) at room temperature. Results showed that they could effectively reduce the friction and wear of sliding pairs compared with the cases without these additives. Especially, C(10)(m(2)im)(2)(NTf(2))(2) showed better antiwear properties with an optimum concentration of 3 wt %, by which a significant improvement of its antiwear property by dozens of times with respect to the base oil was achieved. The excellent tribological properties are attributed to the formation of high-quality physical adsorption films and tribochemical product during friction and the good miscibility of ionic liquids with base oil.