Driving Ionomers Towards Equilibrium: Neutron Spin Echo and Simulations Insight*

From a single molecule to melts, clustering of ionomers drives the formation of far from equilibrium structures. With premise that cluster cohesion controls the path towards equilibrium, our study probes ionic clustering and follows the corresponding impact on the polymer dynamics using neutron spin echo and molecular dynamics simulations. Solutions of 10 Wt% polystyrene sulfonate in toluene, above the overlap concentration are studied as the ionic clusters are perturbed via addition of ethanol. Experimental and computational results for the dynamic structure factor S(q,t), are in excellent agreement. The dynamic data are then correlated with characteristics of ionic clusters attained from the simulations. In toluene, where well defined clusters are formed, the polymer motion is constrained, however below the inter cluster distance motion persists. Though the system contains significant amount of solvent, it is macroscopically locked. Perturbing the clusters through ethanol addition, the clusters are slightly perturbed but sufficient to remove the constraints. These constraint release without fully breaking the clusters impacts the macroscopic dynamics leading towards a shorter path towards equilibrium.