Morphology and Conductivity in Sulfonated Polyphenylenes

Proton conduction in hydrated, proton-conducting polymer membranes is highly affected by hydration level and membrane morphology. Here we examine morphology and dynamics in a promising proton-conducting polymer, a sulfonated Diels-Alder polyphenylene (SDAPP). We performed atomistic molecular dynamics (MD) simulations on a series of SDAPPs, systematically varying the degree of sulfonation and water content to determine their effect on the nanoscale structure, particularly for the hydrophilic domains formed by the ionic groups and water molecules. The static structure factors calculated from simulation are in good agreement with X-ray scattering data. NMR and impedance spectroscopy measurements show that the proton conduction mechanism evolves from being dominated by vehicular transport at low hydration and sulfonation levels to including a significant contribution from the Grötthuss mechanism at higher hydration and sulfonation levels.