Self-organized ionic polymer membranes conduct mobile species (ions, water, alcohols, gases) according to a hierarchy of structural morphologies that span sub-nm to > 10 micron in length scale. Our group combines multi-modal NMR measurements (spectroscopy, diffusometry, relaxometry, imaging) with structural information from scattering and microscopy as well as theories of porous media, electrolytic transport, and oriented matter. Such comprehensive dynamical and structural studies allow for unprecedented understanding of soft matter systems such as ionic polymer membranes used in water purification, fuel cells, and batteries.
Using the wide array of methods known as pulsed-field-gradient (PFG) NMR, one can track chemically distinct moving species as well as vary the measurement encoding time to probe the polymer structures that influence transport. Spectroscopy on deuterated probe molecules and other quadrupole-bearing mobile species can further provide fine measurements of polymer orientational order. This talk will focus on the relations between multi-scale polymer alignment and transport in ionic polymers,1 as well as on the local energetics of transport (< 1 nm scale) probed using PFG-NMR activation energy measurements.2 We will discuss our recent studies that allow quantitative separation of the two major effects that govern transport in polymer membranes: 1) local intermolecular energetics and 2) polymer morphology (e.g., tortuosity) on > 10 nm scales.