Effects of Ionic Group Distribution on the Structure and Dynamics of Amorphous Polymer Melts: Molecular Dynamics Simulations Insight*

Decoration of polymers with ionizable groups results in distinctive structures that drive their dynamics. Their structure is dominated by ionic clusters driven by electrostatic interactions. One significant unresolved  issue is the impact the of distribution of ionizable groups along the polymer backbone on cluster formation and thus on the dynamics of the polymers. Using fully atomistic molecular dynamics simulations, we study the structure and dynamics of amorphous polystyrene sulfonate with random, precise (number of carbons between ionizable groups is exact), and blocky distributions of the ionizable groups along the backbone.  We find that the shape and size distribution of clusters as well as the number of unique chains associated with each cluster are affected by the distribution of the ionic groups.  This in turn influences the structure and dynamics of the polymers as expressed in S(q) and S(q,t).  Precise and blocky distributions exhibit higher interionic domain correlations compared with a random distribution. The mobility of the polymer and counterions is affected by both the number and size of the clusters as well as the number of polymer chains associated with each cluster.