Novel ionic lubricants for amorphous carbon surfaces: molecular modeling of the structure and friction

The present article reports a molecular dynamics study of ammonium based ionic liquids confined between surfaces of amorphous carbon. The ionic liquids studied herein are composed of alkylammonium cations combined with alkylsulfonate anions which due to their environmentally acceptable character are suitable candidates for lubrication. A model was built from first principles describing the interaction between ionic liquids and an amorphous carbon surface. A set of interaction parameters was obtained by fitting density functional theory potential energies of the interaction between fragments of ionic liquids and a cluster of diamond, with a site-site potential function. Molecular dynamics simulations using the developed potentials were performed, and the structure at the solid-liquid interface was analyzed, as well as the orientational order of the alkyl side chains with respect to the surface. Finally, by applying shear and load to the system we predict the friction coefficient at different values of shear velocities.