Influence of Cation Type on Structure and Dynamics in Sulfonated Polystyrene Ionomers

The structure and dynamics of Na-, Cs-, and Zn-neutralized sulfonated polystyrene (SPS) ionomers were investigated using scanning transmission electron microscopy (STEM), X-ray scattering, and dielectric relaxation spectroscopy. Aggregates similar to 2 nm in diameter were revealed by STEM and X-ray scattering. Additional information on aggregate diameter, radius of closest approach, and number density were determined by fitting the scattering data with a modified hard sphere model. A single broad segmental relaxation was identified in dielectric loss spectra for the ionomers neutralized with monovalent ions Cs and Na. The relaxation time of the segmental process was found to slow down systematically with increasing degree of sulfonation but is not significantly affected by monovalent ion type. For Cs-neutralized SPS, two high temperature relaxations associated with Maxwell Wagner Sillars and ion association/disassociation dynamics were identified.