The local symmetry of the sulfonated poly(ether ether ketone) and Nafion exchange sites are correlated to the membrane state-of-hydration, observed and DFT calculated vibrational spectroscopy group modes. At low states-of-hydration the proton is associated and the sulfonic acid exchange site has no local symmetry (i.e., C1). As the membranes hydrates, the C1 group modes gradually vanish while the exchange site dissociates to yield a sulfonate group with a 3-fold axis of symmetry (C3V). C3V group modes increase in intensity as the membrane hydrates. The categorization of side chain group modes in terms of local symmetry is generalized to cation and anion exchange membranes. The Nafion C1 and C3V modes do not co-exist at extreme states-of-hydration but do at intermediate levels of hydration. SPEEK C1 and C3V group modes always co-exist. The implications of these observations on the modes of proton transport versus state-of-hydration are clarified. Preliminary data on quaternary ammonium based alkaline membranes (always C3V) will be presented.

Theoretical and experimental vibrational spectroscopy of ionomers

249th National Meeting (2015)

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