Exploring and tuning the morphologies in coarse-grained polymerized ionic liquids: a molecular dynamics study

Many experimental and simulation studies over the past few decades have shown that block copolymers in bulk can self-assemble into fascinating ordered structures, such as Frank–Kasper (FK) (σ, A15, C14) and dodecagonal quasicrystalline morphologies. Recently, it has been shown that polymerized ionic liquids (PILs) can also undergo microphase separations that result in ionic conductivities over an order of magnitude higher than those in disordered PILs. However, the possible morphologies in PILs, the mechanisms of their formation, and their structural and dynamic properties are still not fully understood.

In our work, we construct and use a soft coarse-grained model with smeared electrostatic interactions to study the different morphologies and phase transitions in PILs. We observe bulk microphase separation in a pure PIL system as the oppositely charged chains become more chemically incompatible, and a spontaneous surface charge separation when metallic electrodes are added, a phenomenon previously reported in coarse-grained monomeric ILs. We show how the ordered structures change as the PIL is mixed with salt or monomeric ILs, as asymmetry is introduced between the polycations and polyanions, and when a potential difference is applied. Furthermore, we examine the ion transport properties in these materials. Our findings may aid the development of PILs for use in energy storage applications and nanostructured functional materials.