FTIR spectroscopy was used to measure the hydrogen-bonding environment of water sorbed into functional polymer membranes. By monitoring of the OD stretch of 10 mol % HOD in H2O, the populations of water bound to the polymer, in the bulk liquid state, and in intermediate states could be deconvoluted rigorously based on their distinct vibrational frequencies. In a series of sulfonated membranes, the negative charge on the sulfonate group computed from density functional theory corresponded with the observed OD frequency for water hydrating the ionic group. Stronger acids, with a lower negative charge on the sulfonate group, displayed a higher frequency OD stretch indicating a weaker hydrogen between water and the acidic headgroup. This FTIR method has been extended to observing how water is bound within the structure of anion exchange membranes and also polyamide reverse osmosis active layers. In addition to directly observing the hydrogen-bonding environment in the OD stretch region, the polymer fingerprint can be examined for changes in vibrational frequency and peak shape of specific functional groups as they are hydrated. Computing difference spectra and the center of mass of key peaks has revealed the important functional groups of the polymer backbone that induce interactions with water. This talk will discuss details of how water interacts with polymer membranes with a variety of chemistries and how these interactions help determine the water transport properties of the materials.

Water hydrogen bonding in functionalized membranes

248th National Meeting (2014)

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