(396f) Interplay of Local Chain Dynamics and Viscoelastic Properties on Liquid Water Transport in Ionomer Nanocomposite Membranes

Nafion/silica nanocomposites are a promising alternative to traditional Nafion membranes for use as proton exchange membranes (PEM) in vanadium redox flow batteries (VRFBs) as they offer an improved resistance to vanadium ion crossover without compromising the beneficial properties of Nafion. However, fundamental understanding of the effect of silica nanoparticles on the transport properties of the nanocomposites is still lacking and it is this understanding that is vital in realizing novel materials specifically tailored for use as PEMs in VRFBs. In this study, in situ time-resolved attenuated total reflectance Fourier transform infrared spectroscopy has revealed that diffusion kinetics of liquid water in Nafion/silica nanocomposites are coupled to the swelling behavior, which is modelled as a stress relaxation phenomenon with a simple three element viscoelastic model. We have attempted to expand on the applicability of this viscoelastic model by studying the changes in the dynamic response of solution-cast Nafion/silica nanocomposites via dynamic mechanical analysis (DMA) and broadband dielectric spectroscopy (BDS) over a range of temperatures. The loss moduli as obtained from DMA and BDS are understood to result from bulk-polymer and inter-phase dynamics, respectively, and are expected to help deconvolute the viscoelastic properties within the hydrophobic and hydrophilic phases of the nanocomposites. The segmental dynamics within the hydrophobic phase of Nafion/silica nanocomposites are also probed via neutron spin echo spectroscopy to derive insights on how the silica interfacial chemistry affects the transport and mechanical response of the nanocomposites. Finally, poroelastic relaxation indentation is used to characterize the poromechanical properties and gain a more holistic insight into the transport behavior of liquid water through these hybrid membranes.