Choline-Based Ionic Liquids on Graphite Surfaces and Carbon Nanotubes Solvation: A Molecular Dynamics Study

The microscopic structure of choline benzoate and choline salicylate at uncharged hydrophobic graphite surfaces, and around and inside single-walled carbon nanotubes with (10,10) and (15,15) armchair configurations, was analyzed using molecular dynamics simulations. The reported results show remarkable structural differences in the vicinity of graphite surfaces (up to 20 angstrom) in comparison with bulk ionic liquids. A remarkable increase of density in the region up to 6 angstrom close to graphite surface is inferred, which is more remarkable for benzoate and salicylate anions than for choline cation. Aromatic rings in benzoate and salicylate anions lie flat at the graphite surface. Choline-based ionic liquids show cylindrical distributions around carbon nanotubes, with the filling of the nanotube depending on the nanotube diameter. The distributions inside the nanotubes rely on the nanotube diameter and are not uniform for the studied anions and cations. Aromatic rings in benzoate and salicylate cations stay parallel to nanotube surfaces.