Effect of side chain length on ionic conductivity in a polymer electrolyte: a semi-generic coarse-grained molecular dynamics study.

Salt-doped poly(oligo-oxyethylene methyl ether methacrylate) (POEM) has attracted attention as an electrolyte due to its reduced crystallinity compared with poly(ethylene oxide) (PEO) resulting from the existence of side chains. Prior work showed that differences in the length of PEO side chains lead to more than an order of magnitude difference in ionic conductivity. We employed a semi-generic model to study this effect, aiming to provide deeper insights to guide experimental study. We viewed the POEM as having a poly(methyl methacrylate) (PMMA) backbone grafted with PEO side chains. We included glass transition temperature (T_g) differences by modifying the like-like interactions, and we applied an angle potential to match the Kuhn length and density of PEO or PMMA. By using a stiff angle potential to create a freely rotating chain, we are able to reproduce the T_g trends of POEM with different side chain lengths. Tuning the LJ potential and solvation potential strength allows us to achieve similar ionic conductivity trends as well. The conductivity with respect to temperature can be fitted by Vogel-Fulcher-Tammann (VFT) equation, corresponding to experimental observations.