Ionomer membrane properties probed with the aid of two-dimensional Fourier transform infrared spectroscopy and quartz crystal microbalance measurements

Polymeric ion conductive materials are widely employed in applications such as analytical separations, chemical sensing and electrical power generation. Studies discussed in this thesis focus on approaches for characterizing molecular scale properties of nanostructured polymer electrolyte membrane. The fluorinated ionomerNafion is used as a model, due to its importance today in low temperature fuel cells and electrochemical sensors. One area of investigation centered on adapting two-dimensional (2D) correlation methods forelucidating structure frominfrared spectral data sets collected during changes in membrane hydration state. Synchronous 2D correlation plots assisted in the resolution of spectral regions complicated by overlapping bands and indicate differences in structural transformationsthat take place during water uptake within hydrophilic relative to more hydrophobic nanoscaleionomer domains. Asynchronous 2D correlation plots reveal relationships in the dynamics of ionomerside chain and backbone motions accompanying changes in membrane hydration state. A second area of investigation centered on adapting the quartz crystal microbalance(QCM) for measurements of membrane water content. Stable responses, sensitive to Nafion membrane preparation conditions, were recorded. The QCM may be useful as a gravimetric method to help assess the influence of non-ideal optical effects in determinations of membrane water content based on infrared spectral measurements.

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