(400h) Effects of Dielectric Inhomogeneity in Ionic Liquids Between Charged Plates

We study the dielectric response of ionic liquids confined between charged plates to develop our self-consistent field mean-field theory (SCMFT) for both incompressible and compressible states. Our theory accounts for the difference between the dipole moments and the molecular volumes of the cation and anion, and the double layer formed through the strong association of the ions with the electrodes. By combining the SCMFT with Monte Carlo simulations, we demonstrate that the hard-core nature of the ions causes oscillations in the density profile near the charged plates. Importantly, our SCMFT captures the effects of spatially varying dielectric value under external electrostatic fields. We illustrate that the effects of the dielectric inhomogeneity and the molecular-volume asymmetry on the spatial distributions of the cations and anions are of approximately equal magnitude and are hence equally important. Furthermore, we show that a contrast in the dielectric values of the cations and anions causes a substantial decrease in capacitance as the applied voltage is increased. Thus, the orientational reorganization of dipoles in ionic liquids can be a critical factor in the strategic control of electrochemical properties in nanostructured materials.