Including polymer stiffness, ion solvation, and glass transition temperature differences in a coarse-grained model of solid polymer electrolytes

Coarse-grained molecular models simplify a system to help show which of its molecular features are most important in setting overall properties, which can be especially helpful for systems with multiple relevant length and time scales such as solid polymer electrolytes. Here, we build on standard, generic bead-spring models, but use stiff angle potentials, set different bead properties for different polymer types, and include additional ion parameters, creating a semi-generic coarse-grained model that can map more specifically to certain polymers and copolymers and better show the effects of their different chain architectures, component glass transition temperatures, and ion solvation behaviors. We set most parameters with basic homopolymer data such as glass transition temperatures, Kuhn length, and dielectric constant, with further adjustment based on data from the polymer electrolyte. We specifically model polystyrene-block-poly(oligo-oxyethylene methyl ether methacrylate) (PS-b-POEM) or homopolymer POEM, with and without lithium triflate salt. Solvation of ions is accounted for by additional polymer-ion interactions of the form -S/r4 or an increased polymer-lithium Lennard-Jones interaction strength. We find these potentials have different effects and discuss strategies for setting these parameters.