Ionomer Nanocomposites: The Interplay Between Structural Dynamics and Water Transport

Ionomer nanocomposites are gaining popularity as proton exchange membranes (PEMs) in vanadium redox flow batteries due to reduced vanadium ion crossover as compared to traditional PEMs. Understanding the impact of silica nanoparticles (SiNPs) on the structural dynamics and transport kinetics of these nanocomposites can provide vital insights into the mechanism of crossover reduction. Presently, segmental and swelling dynamics of a series of ionomer nanocomposite membranes were characterized using neutron spin echo and time-resolved Fourier transform infrared attenuated total reflectance (tFTIR-ATR) spectroscopy. We found that both viscoelastic relaxations and segmental dynamics in the ionomer network were impeded by the presence of SiNPs. Further, the dynamics of the membranes were highly dependent on the surface chemistry of the SiNPs, for both cationically or anionically charged surfaces. In addition to swelling dynamics, tFTIR-ATR was used to evaluate water sorption kinetics, which were found to be strongly coupled with the viscoelastic relaxation in these hybrid membranes. Anomalous, multi-stage water sorption kinetics were observed and attributed to different stages of structural rearrangement in the ionomer network during membrane hydration.