Discrete and Continuum Analyses of Confinement Effects of an Ionic Liquid on the EDL Structure and the Pressure Acting on the Wall

We use both molecular dynamics (MD) and continuum models to analyze the electric double layer structure and pressure acting on the wall of a symmetrically valenced ionic liquid in a nanoconfinement. The nanoslit width varies from 20 times ion size to an ion size, in which the Bazant, Storey, and Kornyshev model may not be compatible. However, the comparison with the MD model shows that the continuum model can successfully predict the averaged charge density and decay of the pressure. The continuum model also shows the exact location of the first and second layer of ions from the confinement wall when considering both steric and correlation effects. However, the continuum model does not account for the oscillatory behaviors of the ion density and the pressure due to the typical characteristics of ionic discreteness, and it slightly overestimates the counterion concentrations compared with the MD analysis. In conclusion, the continuum model can be used to estimate the overall tendency of the pressure acting on the wall when ionic liquid is confined in nanometer thickness, though the oscillatory behavior of the pressure, which originates from the discreteness of ions, cannot be predicted exactly. It can provide useful information in designing nanoporous structures for various electrochemical applications.