Deuteron and oxygen-17 nuclear magnetic resonance measurements and dielectric relaxation studies of Nafion-117 membranes with variable water content (approximately 5-18% by weight) have been carried out. Glassy behavior of the water domains at low temperature, below ca. 200 K, is evidenced by the specific nature of the 2H NMR line shades Actlvahon energms extracted from H spm-lattme relaxation data on the high temperature rode of the T1 minimum exhibit a steady increase with increasing water content. In spite of a high degree of molecular mobility, angular-dependent spectra in both as-received and stretched samples reflect considerable anisotropy of the host polymer. A dielectric loss peak is observed which previously has been attributed to the glass transition of the aqueous domains.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.117.10.200 Downloaded on 2014-11-28 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.117.10.200 Downloaded on 2014-11-28 to IP
Polyimide films containing up to 3.2 wt. % water (H 2 0 or D 2 0) have been studied by dielectric relaxation (DR) and 2H nuclear magnetic resonance (NMR) spectroscopies. Dielectric less measurements show the presence of a double peak near 200 K due to water, with two components designated as Yl and Y2' The Y2 peak, which appears at the lower temperature, is only present for the interior portion of thick (> 25 pm) films and rapidly decreases as the moisture content decreases. Correspondingly, deuteron NMR measurements show the presence of narrow and broad lines, which are correlated, respectively, with the r1 and Y2 DR peaks. The spin-spin relaxation time T 2 , is much longer for the narrow line than for the broad line. The Yl DR peak and the narrow NMR line are attributed to sites where isolated water molecules are only loosely coupled to the polymer chains. Th.e)/2 and bread NMR lines involve small clusters of water molecules with associated nuclear magnetic dipoledipole coupling. Additional measurements on polyimides containing methanol and acetic acid absorbents are also reported.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.