Effects of Side Chain Length on Ionic Aggregation and Dynamics in Polymer Single-Ion Conductors

We employed bead-spring models of polymer single-ion conductors to study the impact of chain architecture on ionic aggregation and dynamics. In most simulations, the ionic aggregates were ordered amorphously, but layered ionic structures were also formed in two cases. Here, we focus on the amorphous systems. The local aggregate structure was determined primarily by the ionic interaction strength, with strong interactions yielding blocky aggregates and weak interactions yielding stringy aggregates. Long side chains increased the conformational freedom of the polymer-bound anions, encouraging greater ionic aggregation. Correspondingly, percolated networks of ionic aggregates were common in the long-side-chain systems, while discrete aggregates were more typical of the short-side-chain systems. The aggregates formed physical crosslinks within the system and, therefore, strongly influenced the dynamics. With strong ionic interactions, cations moved more quickly via a shuttling mechanism through percolated aggregates instead of relying solely on the slow rearrangement of discrete aggregates. However, with weaker ionic interactions, the aggregate morphologies were less important, since the lifetimes of ion association were significantly reduced.