Molecular dynamics simulations of the ionic liquid [BMIM][PF6] confined inside silicon slit nanopores

The structures of [BMIM][PF6] ionic liquids (ILs) inside a silicon slit nanopore of width H = 2.0, 3.0, and 4.0 nm at T = 300 K have been studied using classical MD simulations. It is clearly shown that the imidazolium rings of [BMIM] in the "shell" layer prefers to parallel to the surface of the nanopore. Furthermore, both the mass and number densities of the confined ILs are oscillatory, the high density layers are formed in the vicinity of the silicon surface, which indicates the existence of solid-like high density IL layers in the vicinity of silicon slabs. Our results suggest that the strong interactions as well as the pore sizes between the pore walls and the ILs can significantly affect the structure of the confined ILs. It is also clarified, for the effects of pore size, ILs in 2.0 and 3.0 nm pore are significantly large compared with 4.0 nm pore sizes. In addition, quadruple-layer structure of ILs was completely formed in 2.0 nm pore. besides, these layers exhibit peak densities about 1.8 times larger than those in the bulk ILs.