Effect of Side-Chain on Structure/Property Relationship of PFSA Ionomers

Perfluorosulfonic-acid (PFSA) ionomers are widely used as solid-electrolytes in electrochemical devices where their transport functionality is controlled by its phase-separated morphology. As an electrolyte, ionomer membranes are in contact with the electrodes thereby forming complex interfaces. In addition, in some devices, such as fuel cells, ionomers form additional interfaces within the porous electrodes to maintain ion-conduction to the catalytic nanoparticles. When confined to nanometer-thick films, a PFSA’s functionality differs at these interfaces and becomes sensitive to the interactions with these particles, resulting in a complex polymer response dependent on thickness, substrate and casting conditions. For the next-generation electrochemical devices, there is need to understand PFSA ionomers with chemistries beyond Nafion and how they form interfaces on substrates. This talk highlights the side-chain chemistry and casting effects on structure/function relationships of PFSA membranes and thin films. The interplay between the chemistry and substrate effects are examined to elucidate the factors controlling ionomer film's hydration as well as nanomorphology during film formation, probed by grazing-incidence X-ray scattering (GIXS).