Molecular dynamics simulation studies on the ionic liquid N-butylpyridinium tetrafluoroborate on the gold surface

The study of solid/liquid interface is of great significance for understanding various phenomena such as the nanostructure of the interface, liquid wetting, crystal growth and nucleation. In this work, the nanostructure of the pyridinium ionic liquid [BPy]BF₄ on different gold surfaces was studied by molecular dynamics simulation. The results indicate that the density of the ionic liquids near the gold surface is significantly higher than that in the bulk phase. Cation's tail (the alkyl chain) orients parallel to the surface under all studied conditions. Cation's head (the pyridine ring) orientation varies from parallel to perpendicular, which depends on the temperature and corrugation of the Au(hkl) surface. Interestingly, analysis of simulated mass and number densities revealed that surface corrugation randomizes the cations packing. On smooth Au(111) and Au(100) surfaces, parallel and perpendicular orientations are well distinguished for densely packed cations. While on corrugated Au(110), cations' packing density and order are decreased. Overall, this study explores the adsorption effect of the gold surface on ionic liquids, providing some valuable insights into their behavior on the solid/liquid interface.