Abstract
ABSTRACTPerfluorosulfonic acid ionomers have been widely used as proton‐conducting materials in polymer‐electrolyte membrane fuel cells and their dispersions in polar solvents are used to prepare proton‐conducting membranes as well as catalyst layers. While it has been known that the dispersed particles become monodisperse after heating to 230 °C or above, their size and shape have not been fully characterized yet. Cryogenic transmission electron microscopy images and small‐angle X‐ray scattering profiles of the dilute aqueous dispersions before and after heating to 240 °C have clearly shown that rod‐like particles became significantly shorter cylinders without changing their radii. Particle length distributions were lognormal and average molar mass and dispersity after heating to 240 °C were consistent with the values from size exclusion chromatography. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 813–818
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