Accession Number:

ADA370103

Title:

A NMR Study of Penetrant Diffusion in Nafion and the Associated Morphological Structure

Descriptive Note:

Final rept. 1996-1999

Corporate Author:

CLARK UNIV WORCESTER MA DEPT OF CHEMISTRY

Report Date:

1999-09-28

Pagination or Media Count:

26.0

Abstract:

Pulsed field gradient NMR was used to determine the self diffusion constants for water and ethanol in Nafion Dupont trademark as a function of temperature and concentration. Typical values for water range from 3x10exp -7sq cmsec at a temperature of 300K and a concentration of 2.5 wt water to 1x10exp -3sq cmsec at a temperature of 360K and a concentration of 24 wt. The form of the concentration and temperature dependence of the self diffusion constants is typical of that expected from free volume theory but only some of the regions of the ionomer are expected to be involved in solvent transport. Fluorine -19 magic angle spinning spectra with side band suppression yielded high resolution Fluorine spectra at spinning speeds of 6KHz. Fluorine spin diffusion between resolved resonances was measured to obtain morphological information Xenon-129 NMR was also used to probe the morphology. The apparent domain size associated with the resonance from the pendant ionomer side chain increases with solvent content and is greater in size in the ease of ethanol compared to water. A picture of Nafion morphology as a bicontinuous phase structure is suggested.

Subject Categories:

  • Organic Chemistry

Distribution Statement:

APPROVED FOR PUBLIC RELEASE