Effect of Annealing on Structure and Diffusion in Hydrated Nafion Membranes

Alexey V. Lyulin (Corresponding author), Soumyadipta Sengupta, Anna Varughese, Pavel Komarov, Arun Venkatnathan

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The annealing of polymer electrolyte membranes is known to affect the membrane structure and proton conductivity. The observed changes depend drastically upon the annealing temperatures and cooling rates. In this study, we have performed a fully atomistic classical molecular dynamics simulation of hydrated Nafion at various hydration levels and annealing rates. The simulations show the compression of hydrophobic Nafion domains by larger water clusters, with a strong antiplasticization effect upon hydration, demonstrated by increasing the glass-transition temperature. The close-range proximity of sulfonate-sulfonate groups of Nafion pendant side chains remains unchanged with the simulated cooling rates. The water clusters in hydrated Nafion become more disconnected and larger in size with slower cooling rates/increased annealing time. This results in the decrease of water and hydronium diffusivity and the corresponding conductivity, thereby explaining qualitatively the experimental observations.

Original languageEnglish
Pages (from-to)5058-5066
Number of pages9
JournalACS Applied Polymer Materials
Volume2
Issue number11
DOIs
Publication statusPublished - 13 Nov 2020

Keywords

  • aging
  • glass transition
  • molecular dynamics simulation
  • Nafion
  • polyelectrolyte membrane

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