@article{27862,
  author = {Ahmet Kusoglu and Thomas J Dursch and Adam Z Weber},
  title = {Nanostructure/Swelling Relationships of Bulk and Thin-Film PFSA Ionomers},
  abstract = {<p>Perfluorinated sulfonic acid (PFSA) ionomers are the most widely used solid electrolyte in electrochemical technologies due to their remarkable ionic conductivity with simultanous mechanical stability, imparted by their phase-separated morphology. In this work, the morphology and swelling of PFSA ionomers (Nafion and 3M) as bulk membranes (&gt;10 μm) and dispersion-cast thin films (&lt;100 nm) are investigated to identify the roles of equivalent weight (EW) and side-chain length across lengthscales. Humidity-dependent structural changes as well as different PFSA chemistries are explored in the thin-film regime, allowing for the development of thickness-EW phase diagrams. The ratio of macroscopic (thickness) to nanoscopic (domain spacing) swelling during hydration is found to be affine (1:1) in thin films, but increases as the thickness approaches bulk values, revealing the existence of a mesoscale organization governing the multiscale swelling in PFSAs. Ionomer chemistry, in particular EW, is found to play a key role in altering the confinement-driven structural changes, including thin-film anisotropy, with phase separation becoming weaker as the film thickness is reduced below 25 nm or as EW is increased. For the lower-EW 3M PFSA ionomers, confinement appears to induce even stronger phase separation accompanied by domain alignment parallel to the substrate.</p>},
  year = {2016},
  journal = {Advanced Functional Materials},
  volume = {26},
  pages = {4961 - 4975},
  month = {07/2016},
  doi = {10.1002/adfm.201600861},
}