Semi-Empirical Molecular Modeling Methods of Ionic Liquid Tribology: Ionic Liquid-Hydroxylated Silicon Surface Interactions

Abstract

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.