No abstract

The interactions between selected ionic liquids and modified silicon surfaces are modeled in this article using semi-empirical methods. The modeled ionic liquids include a series of ionic liquids consisting of imidazolium derivatives with Cl -as the anion interacting with hydroxylated silicon wafers. A second series consists of symmetrical and asymmetrical dicationic imidazolium derivatives with PF 6 -or BF 4 -as the anion interacting with hydroxylated single crystal silicon wafers. The tribological properties of these ionic liquids and their interactions with silicon surfaces are modeled using a rolling hydroxylated silicon surface. The ionic liquids are allowed to form a complex with this surface, and the enthalpies of complex formation are seen to correlate with the tribological properties of the ionic liquids.

Raman and infrared spectra of trimethylsulfonium dicyanamide [(CH(3))(3)SN(CN)(2)] are reported and accurately reproduced by DFT methods (B3LYP and B3PW91), MP2, and MP3, and to a lesser extent by the RHF method. The (CH(3))(3)SN(CN)(2) ionic liquid forms two isomeric dimers that are of cyclic structure, one of which is 13 kcal/mol lower in energy than the other. Both isomeric cyclic pairs (versions 1 and 2), [(CH(3))(3)SN(CN)(2)](2), have the potential to further combine and form a common structure containing four pairs of (CH(3))(3)SN(CN)(2). This structure can then conceivably undergo a stacking procedure to form extended ionic liquid nanotubes of eight ionic liquids, [(CH(3))(3)SN(CN)(2)](8). The possible formation of gas phase ionic liquid clusters of two, four, and eight trimethylsulfonium dicyanamide ionic liquids is supported by highly exergonic free energy changes obtained from B3LYP/(6-311+G(d,p)) density functional calculations.

The interactions between the selected ionic liquids (ILs) and aluminum oxide surfaces are modeled in this report using theoretical methods. A wide range of ILs and their interactions with an aluminum oxide surface are modeled using the PM5 semi-empirical method. The ILs modeled in this study contain imidazolium (C 3, 4, 6, 8 or 10 mim) or ammonium cations including (C 6 H 13 ) 3 NH ? , (C 8 H 17 ) 3 NH ? , C 8 H 17 NH 3? , (C 2 H 5 ) 3 NH ? , and (C 8 H 17 )NH 3 ? . The anions include Cl -, Br -, PF 6 -, (CF 3 SO 2 ) 2 N -, and (C 2 F 5 SO 2 ) 2 N -. The interactions of these ILs with an Al-O surface are modeled in a stepwise manner. The lowest energy forms of the individual ILs are determined, and these ILs are allowed to form a complex with the Al-O surface. The resulting reaction enthalpies of ionic liquid-surface complex formation are seen to correlate with the tribological properties of the ILs. The strongest correlations occur within those ILs containing similar cations.

The interactions between eight ionic liquids and a rolling hydroxylated silicon surface are modeled in this report using various semi-empirical methods. The eight modeled ionic liquids consist of two sets for four ionic liquids from separate tribology studies. The first set of four ionic liquids contain the 1-butyl-3-methyl imidazolium cation (BMIM+) and include BMIM+-BF4-, BMIM+-NO3-, BMIM+-PF6- and BMIM+-ClO4-. The second set of ionic liquids contains the 1-methyl-3-X imidazolium cation and a Cl- anion. The four imidazolium sidechains (X) include -C3H6OH, -C2H4CN, -C3H7 and -C2H4COOH. The individual ionic liquids form complexes with the hydroxylated silicon surface and the enthalpies of complex formation calculated using PM3, PM5 and PM6 semi-empirical methods. The PM3 and PM5 computed ionic liquid-surface complex ΔrH enthalpies of complex formation correlate with the measured frictional coefficients of these ionic liquids. These results allow the investigator to possibly predict the success or failure of other ionic liquids once a baseline is established.