Clustering Effects on Dynamics in Ionomer Solutions: A Neutron Spin Echo Insight

Ionizable blocks in ionomers associate into aggregates serving as physical cross-links and concurrently form transport pathways. The dynamics of ionomers underline their functionality. Incorporating small numbers of ionic groups into polymers significantly constraint their dynamics. Recent computational studies demonstrated a direct correlation between ionic cluster morphology and polymer dynamics.$^{\mathrm{1}}$ Here using neutron spin echo, we probe the segmental dynamics of polystyrene sulfonate (PSS) as the degree of sulfonation of the PSS and the solution dielectrics are varied. Specifically, 20Wt{\%} PSS of 11,000 g/mol with polydispersity of 1.02 with 3{\%} and 9{\%} sulfonation were studies in toluene (dielectric constant $\varepsilon \quad =$2.8), a good solvent for polystyrene, and with 5Wt{\%} of ethanol ($\varepsilon \quad =$24.3l) added. The dynamic structure factor S(q,t) was analyzed with a single exponential except for a limited q range where two time constants associated with constraint and mobile segments were detected. S(q,t) exhibits several distinctive time and length scales for the dynamics with a crossover appearing at the length scale of the ionic clusters. 1)Agrawal et. al Phys. Rev. Lett.~\textbf{116}, 158001