Cluster Cohesion Effects on Segmental Dynamics in Ionic Polymer Solutions: Molecular Dynamics Simulation Studies*

A small number of ionizable groups tethered to a polymer backbone restricts their macroscopic dynamics. Here, using molecular dynamic (MD) simulations, the dynamics of sulfonated polystyrene (PSS) in toluene solutions are studied as the ionic domains are perturbed by small amounts of ethanol. The static and dynamic structure factors, S(q) and S(q,t) were calculated. S(q) exhibits a characteristic ionic domain signature that is affected by ethanol content. S(q,t), analyzed by KWW resolved two dynamic regions. At low ethanol concentrations, segmental dynamics increase, followed by constrained motion with increased alcohol concentration. Initially, the ionic domains swell, enabling segmental motion. Higher ethanol concentrations collapse the PS segments restricting the motion. These MD results are in excellent agreement with our neutron spin echo data.