Frictional dynamics of alkylsilane monolayers on SiO₂: Effect of 1-n-butyl-3-methylimidazolium nitrate as a lubricant

The effect of 1-n-butyl-3-methylimidazolium nitrate ionic liquid (IL) on the shear dynamics and tribological properties of contacting ordered alkylsilane self-assembled monolayers (SAM) on SiO₂ surfaces was studied using molecular dynamics simulation. Use of the IL as a lubricant was found to reduce the friction between the contacting monolayers in the studied range of applied loads. At low applied loads, complex behavior in the dependency of the frictional force on the normal load in both lubricated and dry monolayers is observed and is shown to be due to the rearrangement of the SAM chains under shear. In contrast, this dependency was found to be linear at high normal loads. The simulations also indicate that the ordering of the SAM chains may be disrupted by penetrating lubricant molecules, suggesting that the IL could incorporate into a damaged area of the SAM coating and restore tribological properties. To our knowledge, this is the first simulation study of the effect of an IL lubricant on the frictional dynamics of SAMs.