Group Vibrational Mode Assignments as a Broadly Applicable Tool for Characterizing Ionomer Membrane Structure as a Function of Degree of Hydration
Abstract
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.
Additional Information
© 2020 American Chemical Society. Received: October 1, 2019; Revised: February 13, 2020; Published: February 14, 2020. Funding was provided Northeastern University, University of Texas Rio Grande Valley, NuVant Systems Inc., and the Army Research Office (W911NF-17-1-0557). Thanks are due to Claudio Oldani of Solvay Specialty Polymers, Italy S.p.A. for providing samples of Aquivion and helpful comments. Thanks to Daniel Mainz at Schrodinger and Chris Drozdowski and Zheng Shao at Origin Lab Corporation for their very helpful assistance with coding. The China Scholarship Council Grant is gratefully acknowledged by Shuitao Gao. Author Contributions: The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest.Attached Files
Supplemental Material - Videos_1-29.zip
Supplemental Material - cm9b04037_si_001.pdf
Supplemental Material - cm9b04037_si_002.xyz
Supplemental Material - cm9b04037_si_003.xyz
Supplemental Material - cm9b04037_si_004.xyz
Supplemental Material - cm9b04037_si_005.xyz
Supplemental Material - cm9b04037_si_006.xyz
Files
Name | Size | Download all |
---|---|---|
md5:a7a8ae80381980245195544458a17860
|
567.2 kB | Download |
md5:7d4ddd6e6f221591b5b5a34bef9896c2
|
718.3 kB | Download |
md5:fc2443ab458ab9a37408885bd87a68f5
|
17.9 MB | Preview Download |
md5:fd78136dcc96f5550e828261c4785573
|
588.6 kB | Download |
md5:195cabc8944ad75dd70ca1ce278d8100
|
827.0 kB | Download |
md5:fca427f135aceea5688bc74dc7c78455
|
249.3 kB | Preview Download |
md5:2b431bac6b5f4a2854e8517db1e0d107
|
1.1 MB | Download |
Additional details
- Eprint ID
- 101313
- Resolver ID
- CaltechAUTHORS:20200214-150525814
- Northeastern University
- University of Texas Rio Grande Valley
- NuVant Systems Inc.
- W911NF-17-1-0557
- Army Research Office (ARO)
- China Scholarship Council
- Created
-
2020-02-14Created from EPrint's datestamp field
- Updated
-
2021-11-16Created from EPrint's last_modified field
- Other Numbering System Name
- WAG
- Other Numbering System Identifier
- 1368