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A Small-Angle X‑ray Scattering Study of the Development of Morphology in Films Formed from the 3M Perfluorinated Sulfonic Acid Ionomer
An extensive SAXS investigation of the 3M perfluorinated
sulfonic
acid ionomer was performed to investigate the morphological changes
that occur during and after annealing at temperatures above the <i>T</i><sub>α</sub>. The effect of film thickness in the
range studied, 11–45 μm, was found to be negligible.
These properties were studied as a function of equivalent weight from
700 to 1100 and correlated with the water uptake as measured by dynamic
vapor sorption. Isoscattering points were observed in dynamic annealing
experiments of the unboiled annealed films at <i>q</i> =
0.023, 0.096 Å<sup>–1</sup>. On initial water uptake these
films also showed isoscattering points at <i>q</i> = 0.024,
0.220 Å<sup>–1</sup>; <i>q</i> = 0.029, 0.223
Å<sup>–1</sup>; and <i>q</i> = 0.030, 0.211
Å<sup>–1</sup> at 50, 80, or 95 °C, respectively,
indicating a decrease in the symmetry of the scattering objects in
these size regimes. Isoscattering points were absent in similar water
uptake experiment for the films after boiling