Morphological Transitions in Ionomer Thin Films

Perfluorosulfonic acid ion-conducting polymers (PFSA ionomers) are a key component to electrochemical catalyst layers, where they exist as nanometer-thick thin films. While it is known that these thin films deviate from their bulk morphology due to confinement and substrate interactions, the origin of such phenomena remains unknown. In this talk, a systematic investigation of different PFSA chemistries, thicknesses, and processing conditions is used to elucidate the driving forces for nanophase separation under confinement. Investigations include the effect of annealing temperature, as well as side-chain density and composition, on the film morphology using grazing incidence x-ray scattering (GIXS). The GIXS data is correlated to water uptake and swelling via simultaneous quartz-crystal microbalance (QCM) and ellipsometry to identify the impact of morphology on thermodynamic properties.