Virginia Tech
Multiscale Tortuous Diffusion in Anion- and Cation-Exchange Membranes: Exploration of Counterions, Water Content, and Polymer Functionality
Abstract
dc:description.abstractFundamental understanding of water transport and morphology is critical for improving ion conductivity in polymer electrolyte membranes (PEMs). Herein, we present comprehensive water transport measurements comparing anion-exchange membranes (AEMs) based on ammonium-functionalized poly(phenylene oxide) and cation-exchange membranes (CEMs) based on sulfonated poly(ether sulfone). We investigate the influence of counter ions, alkyl side chain, and degree of functionalization on water transport in AEMs and CEMs using pulsed-field-gradient (PFG) NMR diffusometry. Water diffusion in both AEMs and CEMs exhibit specific trends as a function of water uptake (wt%), indicating morphological similarities across common chemical structures. Furthermore, restricted diffusion reveals micron-scale heterogeneity of the hydrophilic network in both CEMs and AEMs. We propose a model wherein the hydrophilic network in these membranes has micron-scale distributions of local nm-scale dead ends, leading to changes in tortuosity as a function of water content, counterion type, and polymer structure. We furthermore parse tortuosity into two regimes, corresponding to nm-to-bulk and µm-to-bulk ranges, which reveal the importance of multi-scale morphological structures that influence bulk transport. This study provides new insights into polymer membrane morphology from nm to µm scales with the ultimate goal of controlling polymeric materials for enhanced fuel cells and other separations applications
Degree
thesis:*- Name thesis:degree_name
- MS
- Level thesis:degree_level
- masters
- Discipline thesis:degree_discipline
- Macromolecular Science and Engineering
- Department dc:contributor.department
- Chemistry
- Grantor dc:publisher
- Virginia Tech
- Year dc:date.issued
- 2017
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Thieu, Lam Mai
- Chair dc:contributor.committeechair
-
- Madsen, Louis A.
- Committee members dc:contributor.committeemember
-
- Deck, Paul A.
- Dorn, Harry C.
Subjects
dc:subject × 6Rights
dc:rights- Statement dc:rights
-
- In Copyright
- Licence dc:rights.uri
Identifiers
dc:identifier.*- Dc Identifier Other
- vt_gsexam:13066
- OAI identifier oai:identifier
- oai:vtechworks.lib.vt.edu:10919/88849