Generic Coarse-Grained Molecular Dynamics Simulations of Ion-Containing Polymers

Ion-containing polymers can be challenging to model due to their strong ion-ion and ion-polymer interactions as well as important features on disparate length and time scales arising from ion, segmental, and overall chain behavior. We study ion-containing systems starting from a generic Kremer-Grest type of model that captures monomer packing and noncrossability of chains and adding long-ranged Coulomb interactions between ions scaled by a background dielectric constant. Depending on the system, further features such as adjusted monomer-monomer interactions to account for chemical differences in copolymers, adjusted monomer and ion sizes, and special ion-monomer potentials to account for ion solvation can be added. Copolymeric systems are especially complex as they may have microphase separated regions with significantly different dielectric strengths and degrees of ion solvation. We typically apply a uniform background dielectric strength; we set this to represent the average dielectric strength for mixed systems or the higher dielectric medium for strongly microphase separated systems (in which the ions exist in the higher dielectric microphase). We also adjust the higher dielectric monomer to ion interactions, often using an ion-monomer potential of the same form as the interaction between an ion and an induced dipole. Recently, we instead applied a classical Drude oscillators model to account for both ion solvation and dielectric strength effects in a greater level of detail. Specifically, polarizable monomer beads are represented by a partially charged bead (that is otherwise similar to the beads of the prior model) with an oppositely charged Drude particle attached to its center by a strong spring. Here we will discuss the implications for ion solvation effects and computational expense.