Dynamic Light Scattering Study of Sulfonated Polystyrene Ionomers in Benzene

From golf ball coatings (Surlyn®) to fuel cell membranes (Nafion®), ionic polymers (ionomers) are widely used. Ionomers are molecular compounds that contain long hydrocarbon chains with ions randomly distributed along the chain. These polymers form ionic aggregates when ionic groups attract each other in nonpolar environment, and these interactions dictate the properties exhibited. We studied the aggregation of sulfonated polystyrene (SPS) ionomers of varying molecular weights and ion contents in benzene. Dynamic light scattering (DLS) experiments determine the effective diameter and the polydispersity of the aggregates and molecules in the solution. To do this, we created solutions of the SPS and its acidic equivalent in benzene at different concentrations and analyzed the scattering. We also studied the effects of an ionic liquid, BMIM-PF₆ (1-butyl-3-methylimidazolium hexafluorophosphate) on SPS ionomers of higher ion contents. It was found that the ionic liquid weakens the ionic bonds and partly destroys ionic aggregates. We will study the properties of ionomers with high ion contents with other ionic liquids and with toluene as a solvent, for comparisons.