Investigation of the Morphological Changes in Nafion Membranes Induced by Swelling with Various Solvents.

摘要

The structure of Nafion 117 pertluorosulfonate ionomer membranes has been investigated using small-angle neutron-scattering techniques. Structural changes induced by swelling of the membranes with water, alcohols, and dipolar aprotic solvents were monitored, at solvent swelling levels ranging from (caret) 2% to > 50%, by volume. Membranes swollen up to (caret) 50 volume-percent 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 q values as the solvent content in the membrane increased. The shift in the position of both maxima was linearly related to the volume fraction of solvent in the membrane. The Bragg spacings corresponding to both the ionic feature scattering maximum and the crystalline feature scattering maximum were plotted vs. volume fraction of solvent in the membranes and the data fit using linear regression. The slopes associated with the spacing vs. volume fraction solvent curves were greater for the crystalline feature spacing than for the ionic feature spacing for all solvents other than water, indicative of preferential segregation of non-aqueous solvents into regions of the structure not directly associated with the ionic scattering maximum.