Analysis of Dielectric Constant and Solvation Energy in Coarse-Grained Polymerized Ionic Liquid Simulation

Recent investigations into the dielectric properties of Ionic Liquids (IL) and Polymerized Ionic Liquids (PIL) indicate further theoretical studies are required for these materials. Some of these works suggest that polymerization of cations in ILs can result in an unconventional increase in the dielectric constant, the mechanism for which is not yet well understood. Additionally, it has been shown that the Born Solvation Energy can be quantitatively inaccurate for monovalent and divalent ions in inorganic non-polymerized solvents, so it is unclear if it can be used in Mean-Field theories for predicting IL and PIL behavior. We seek to probe these results with molecular dynamics simulation using the Stockmayer Fluid model, where all molecules are treated as Lennard-Jones spheres with permanent dipole moments and point charges. By varying ionic charge we analyze the dielectric constant, dipolar orientational order and correlation, and compare simulated solvation energy with the expected Born Solvation energy. A significant increase in the dielectric constant upon polymerization is found at low values of ionic charge, but the inclusion of local ion pairs into the calculation suggest large charges may show this as well. We also find that increases in the dielectric constant are generally associated with increases in order and correlation length. This suggests that the large increase in the dielectric constant results from increased order that occurs upon polymerization. Further, the energy per ion of the simulations can match that expected with the Born Solvation energy if scaled with an effected ionic radius, which is justified by our results from the radial distribution function.