Improving the Lubrication of Silicon Surfaces Using Ionic Liquids as Oil Additives: The Effect of Sulfur-Based Functional Groups

The performance of micro/nanoelectromechanical systems (MEMS/NEMS) relies on efficient lubrication. In the present work, new sulfur-based organic salts were tested as additives in a polyethylene glycol to lubricate silicon surfaces used in the manufacture of MEMS/NEMS. Seven salts were tested: 1-butylsulfonic-3-methylimidazolium triflate [(C₄SO₃H)MIM][TfO], thiamine triflate [Thiamine][TfO]₂, 1-ethyl-3-methylimidazolium camphorsulfonate [C₂MIM][CSA] [isomers (R) and (S)], 1,3-dimethylpiridinium methylsulfate [C₁-3pic][MeSO₄], methylimidazolium methanesulfonate [HMIM][MeSO₃], and tetramethylguanidine methanesulfonate [TMG][MeSO₃]. A nanotribometer was used to determine the friction coefficients using steel spheres as counter bodies. Excellent tribological properties were achieved with the additives containing the anions [MeSO₄]⁻ and [MeSO₃]⁻. The films formed on the Si substrates were studied by FTIR, ellipsometry and AFM. A mixed lubrication mechanism was proposed where additive adsorption avoids contact between sliding surfaces. Graphical Abstract: [Figure not available: see fulltext.].