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Group Vibrational Mode Assignments as a Broadly Applicable Tool for Characterizing Ionomer Membrane Structure as a Function of Degree of Hydration

Loupe, Neili and Abu-Hakmeh, Khaldoon and Gao, Shuitao and Gonzalez, Luis and Ingargiola, Matthew and Mathiowetz, Kayla and Cruse, Ryan and Doan, Jonathan and Schide, Anne and Salas, Isaiah and Dimakis, Nicholas and Jang, Seung Soon and Goddard, William A., III and Smotkin, Eugene S. (2020) Group Vibrational Mode Assignments as a Broadly Applicable Tool for Characterizing Ionomer Membrane Structure as a Function of Degree of Hydration. Chemistry of Materials, 32 (5). pp. 1828-1843. ISSN 0897-4756. doi:10.1021/acs.chemmater.9b04037.

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[img] PDF (Instructions for running MD simulations on Nafion sulfur-centered 10 Å cubes and creating histograms for data, macros used in the Microsoft Excel Visual Basic for Applications (VBA) programming language, histogram data for five different values of λAvg...) - Supplemental Material
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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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Loupe, Neili0000-0003-0718-428X
Ingargiola, Matthew0000-0001-7764-307X
Cruse, Ryan0000-0003-3209-4657
Doan, Jonathan0000-0002-6064-9421
Dimakis, Nicholas0000-0003-2478-237X
Jang, Seung Soon0000-0002-1920-421X
Goddard, William A., III0000-0003-0097-5716
Smotkin, Eugene S.0000-0002-9629-0414
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.
Funding AgencyGrant Number
Northeastern UniversityUNSPECIFIED
University of Texas Rio Grande ValleyUNSPECIFIED
NuVant Systems Inc.UNSPECIFIED
Army Research Office (ARO)W911NF-17-1-0557
China Scholarship CouncilUNSPECIFIED
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Issue or Number:5
Record Number:CaltechAUTHORS:20200214-150525814
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Official Citation:Group Vibrational Mode Assignments as a Broadly Applicable Tool for Characterizing Ionomer Membrane Structure as a Function of Degree of Hydration. Neili Loupe, Khaldoon Abu-Hakmeh, Shuitao Gao, Luis Gonzalez, Matthew Ingargiola, Kayla Mathiowetz, Ryan Cruse, Jonathan Doan, Annie Schide, Isaiah Salas, Nicholas Dimakis, Seung Soon Jang, William A. Goddard, III, and Eugene S. Smotkin. Chemistry of Materials 2020 32 (5), 1828-1843; DOI: 10.1021/acs.chemmater.9b04037
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101313
Deposited By: Tony Diaz
Deposited On:14 Feb 2020 23:14
Last Modified:16 Nov 2021 18:01

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