Small-angle neutron scattering investigation of structural changes in nafion membranes induced by swelling with various solvents

Authors

  • Sandra K. Young,

    1. U.S. Army Research Laboratory, Weapons & Materials Research Directorate, AMSRL-WM-MA/Building 4600, Aberdeen Proving Grounds, Maryland 21005-5169
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  • S. F. Trevino,

    1. U.S. Army Research Laboratory, Weapons & Materials Research Directorate, AMSRL-WM-MA/Building 4600, Aberdeen Proving Grounds, Maryland 21005-5169
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  • Nora C. Beck Tan

    Corresponding author
    1. U.S. Army Research Laboratory, Weapons & Materials Research Directorate, AMSRL-WM-MA/Building 4600, Aberdeen Proving Grounds, Maryland 21005-5169
    • W. L. Gore & Associates, 501 Vieve's Way, Elkton, MD 21922
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  • Certain commercial products are identified in this article to specify the experimental procedures in adequate detail. This identification does not imply recommendation or endorsement by the authors or by the National Institute of Standards and Technology, nor does it imply that the products identified are necessarily the best available for the purpose.

Abstract

The structure of Nafion-117 perfluorosulfonate ionomer membranes was investigated with small-angle neutron scattering techniques. Structural changes induced by the swelling of the membranes with water, alcohols, and dipolar, aprotic solvents were monitored at solvent-swelling levels ranging from approximately 2 vol % to greater than 50 vol %. Membranes swollen up to approximately 50 vol % solvent exhibited two scattering maxima, one known to be associated with ionic regions of the membrane structure and one known to be associated with correlation distances between crystalline regions in the membrane structure. The positions of both maxima shifted toward lower scattering vector values as the solvent content in the membrane increased. The shift in the position of both maxima was linearly related to the solvent volume fraction in the membrane. The Bragg spacings corresponding to both the ionic-feature scattering maximum and the crystalline-feature scattering maximum were plotted versus the solvent volume fraction in the membranes, and the data fit with linear regression. The slopes associated with the curves of the spacing versus the solvent volume fraction were greater for the crystalline-feature spacing than for the ionic-feature spacing for all solvents other than water; this was indicative of preferential segregation of nonaqueous solvents into regions of the structure not directly associated with the ionic scattering maximum. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 387–400, 2002; DOI 10.1002/polb.10092

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