Group Vibrational Mode Assignments as a Broadly Applicable Tool for Characterizing Ionomer Membrane Structure as a Function of Degree of Hydration
| Autor: | Seung Soon Jang, Jonathan Doan, Annie Schide, Kayla Mathiowetz, Shuitao Gao, Matthew Ingargiola, Khaldoon Abu-Hakmeh, Isaiah Salas, Eugene S. Smotkin, Neili Loupe, Ryan Cruse, Nicholas Dimakis, William A. Goddard, Luis E. González |
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| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
Materials science
General Chemical Engineering Membrane structure Infrared spectroscopy 02 engineering and technology General Chemistry 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences chemistry.chemical_compound Membrane Sulfonate chemistry Group (periodic table) Nafion Materials Chemistry Physical chemistry 0210 nano-technology Ionomer |
| Popis: | Infrared spectra of Nafion, Aquivion, and the 3M membrane were acquired during total dehydration of fully hydrated samples. Fully hydrated exchange sites are in a sulfonate form with a C₃V local symmetry. The mechanical coupling of the exchange site to a side chain ether link gives rise to vibrational group modes that are classified as C₃V modes. These mode intensities diminish concertedly with dehydration. When totally dehydrated, the sulfonic acid form of the exchange site is mechanically coupled to an ether link with no local symmetry. This gives rise to C₁ group modes that emerge at the expense of C₃V modes during dehydration. Membrane IR spectra feature a total absence of C₃V modes when totally dehydrated, overlapping C₁ and C₃V modes when partially hydrated, and a total absence of C₁ modes when fully hydrated. DFT calculated normal mode analyses complemented with molecular dynamics simulations of Nafion with overall λ (λ_(Avg)) values of 1, 3, 10, 15 and 20 waters/exchange site, were sectioned into sub-cubes to enable the manual counting of the distribution of λ_(local) values that integrate to λ_(Avg) values. This work suggests that at any state of hydration, IR spectra are a consequence of a distribution of λ_(local) values. Bond distances and the threshold value of λ_(local), for exchange site dissociation, were determined by DFT modelling and used to correlate spectra to manually counted λ_(local) distributions. |
| Databáze: | OpenAIRE |
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