Effects of Molecular Polarity and Polymerization on Ion Solvation in Polymer Melts

We study the solvation energy of ions in polymerized and non-polymerized dipolar solvents using molecular dynamics simulations. We use a coarse-grained Stockmayer fluid model to observe the effects on solvation energy for monovalent, divalent, and trivalent ions due to varying solvent dipole moments. We show that increasing polymer chain lengths leads to significantly more negative solvation energies of ions. This is because in polymerized solvents, chain connectivity leads to higher local packing fraction of solvent dipoles near the ion and hence a stronger dielectric response. Also, there is a substantial difference between simulation results and the predicted Born solvation energy using Onsager theory for dielectrics. We hypothesize that the compressibility of solvents and local dipolar structure are key to understanding the difference between simulated and predicted results.