New Protic Ionic Liquids as Potential Additives to Lubricate Si-Based MEMS/NEMS

Abstract

The motivation for this work was to develop new protic ionic liquids (PILs) as additives for the lubrication of micro and nanoelectromechanical systems (MEMS and NEMS). Ten PILs based on the combination of methylimidazolium ([MIMH]), 4-picolinium ([4-picH]), pyridinium ([PyrH]), 1,8-diazabicyclo[5.4.0]-undec-7-ene-8-ium ([DBUH]) and tetramethylguanidinium ([TMGH]) cations with hydrogen sulfate([HSO4]) and mesylate ([MeSO3]) anions were tested as additives in polyethylene glycol (PEG200) to lubricate steel/silicon and silicon/silicon contacts. The best additive was [4-picH][HSO4], which adsorbed strongly on the Si surface, leading to a protective film that reduced wear by up to 15 times compared to PEG200.

Molecular Interactions between Ionic Liquid Lubricants and Silica Surfaces: An MD Simulation Study

“…The inspection of Figures and S12 indicates that the distance between PEG200 molecules and the glass surface decreases when 2% (w/w) [4-picH][HSO 4 ] is present. In other words, the presence of the 2% of PIL leads to the formation of a compact protective film on the surface, corroborated by the reduction in CoF and wear in Figure . In close contact with the glass substrate, the OH groups of pure PEG200 can perform H bonds with neighboring PEG200 molecules, as seen on TRDFs presented in Figure S13a,b in the SI.…”

“…The errors are ± standard deviation ( n ≥ 3). The values for the mixtures with [4-picH]­[HSO 4 ] and [4-picH]­[MeSO 3 ] were taken from a previous work …”

“…The MD results for the ILs near the amorphous silica interface have indicated that there are preferential interactions between [4-picH]­[HSO 4 ] and the glass surface. Also, the experimental data revealed good tribological performance of [4-picH]­[HSO 4 ] as an additive in PEG200 to lubricate silicon/silicon contacts as well as steel/silicon pairs . First, the snapshots of the MD simulations of the bulk mixtures of PEG200 with [4-picH]­[HSO 4 ] at concentrations 2, 5, and 20% (w/w) are presented in Figure and the aggregate probability distribution functions for the corresponding systems are depicted in Figure S11 in the SI.…”

“…The syntheses of the PILs are described in detail in our previous work . The syntheses of [C 6 mim]­[HSO 4 ] and [C 6 mim]­[MeSO 3 ] are described in the Supporting Information.…”

“…The capacity of protic ionic liquids (PILs) to lubricate silicon surfaces was recently investigated by our group. 23 PILs are ionic liquids composed of Brønsted acids and bases, whose unique properties are conferred by the presence of proton-donor and proton-acceptor sites leading to dense hydrogen bonding. PILs are easily prepared by simple protonation of the cation using appropriate acids, and their price is lower compared to other ILs.…”