Dynamics in Ionizable Polymer Blends: Computational Insight

To realize the full potential of ionizable polymers, their mechanical stability needs to be enhanced. Blending with additional polymers provides a promising path. Using atomistic molecular dynamics simulation, we examine the development of polystyrene (PS): sulfonated polystyrene (PSS) blends with the hypothesis that the ionic assemblies will control the dynamics of the polymer molecules and, consequently, their blending. Surprisingly, even at a low sulfonation fraction f = 0.05, with approximately one S atom per chain, PS and PSS phase segregate. The structure factor S(q), monitored over time for each polymer, reveals that at f = 0.05, a low q signature corresponding to the development of domains for each polymer increases over time, as expected for phase segregation. For f = 0.1 and 0.2, S(q) does not exhibit a signature of domain evolution, indicating that the systems are kinetically trapped. These blends were perturbed by modulating the clusters through changing the dielectric constants, which decreases the size of the ion clusters. The mean square displacement of the center of mass of polymer chains reveals reduced chain mobility at higher sulfonation levels when the systems appear homogeneous. The dynamic process in blends will be discussed in comparison with melts.