Interfaces between charged surfaces and ionic liquids: Insights from molecular simulations

Molecular Dynamics (MD) simulations of ionic liquid-electrode interfaces show that a transition from a multilayer ion structure to an ordered monolayer structure can be observed at certain values of the surface charge density. Upon this transition, a distinct change in the surface charge excess in the first two interfacial layers can be seen as a function of the renormalized surface charge density. The degree of ordering in the innermost ion layer increases upon increasing the surface charge density, while the transition region exhibits systematic transformations upon surface charging. The point of maximum layering in the transition region depends on the density of the ionic liquid as well as on the ion-ion and ion-electrode interactions. The packing density of ions at the interface can be further increased upon surface charging without crowding up to the monolayer structure formation.