Disjoining pressure of room temperature ionic liquid in charged slit carbon nanopore: Molecular dynamics study

Abstract

We present a study of the behavior of the room-temperature ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) in negatively charged carbon slit nanopores of various widths (1 ÷ 15 nm) using all-atom and coarse-grained molecular dynamics simulations. For the room temperature ionic liquids, we calculate and analyze the disjoining pressure as a function of pore width from the all-atom and coarse-grained molecular dynamics simulations. We discuss the damped oscillations of the disjoining pressure for sufficiently small pore widths and elucidate their microscopic nature. We also analyze radial distribution functions, and angle distributions charge, mass, and number densities of the ionic liquid inside the pore. We find that a confined ionic liquid has a layering structure inside the pore of <5 nm in width. We show that the cations in the layer closest to the charged surfaces are in parallel orientation and form a lamellar-like structure. We observe charge overcompensation near the graphene surfaces at σ = −12.8 μC/cm2 and the lattice saturation effect at σ = −41.6 μC/cm2. Based on the disjoining pressure behavior, we estimate the effective electrostatic screening length.