Evolution of morphology, segmental dynamics, and conductivity in ionic liquid swollen short side chain perfluorosulfonate ionomer membranes

Jun Hong Lin, Ralph H. Colby

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1273-1280 Many authors have observed a critical uptake where both the conductivity and electroactive responses of ionic liquid (IL) swollen ionomer actuators improved markedly. In this work, the mechanical dynamics, conductivity, and morphology of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) swollen Aquivion membranes are explored. The absorbed EMI-Tf is mainly bounded in the cluster region of Aquivion. Despite the observed critical uptake effects, the segmental relaxation frequency still plays a major role for the ionic conduction in these IL swollen membranes over a broad uptake range.

We investigate the morphology, segmental dynamics, and conductivity of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) swollen short side chain perfluorosulfonate ionomer (Aquivion) over a broad uptake range using small angle X-ray scattering (SAXS), dielectric relaxation spectroscopy, and transient current measurement. The SAXS data indicate that the absorbed EMI-Tf is mainly bounded in the ionic region of Aquivion. At low uptakes, EMI-Tf acts as an effective plasticizer lowering the cluster Tg and markedly shifting the segmental relaxation to a high frequency; however, at high uptakes, the additional EMI-Tf acts like a filler instead. A time-domain model was employed to quantify the conductivity of these membranes containing two mobile ion species, that is, cations and anions. The conductivity of both neat EMI-Tf and EMI-Tf swollen membranes exhibits Vogel-Fulcher-Tamman relation, revealing different activation parameters for ionic conduction. Furthermore, membranes containing different EMI-Tf uptakes have similar conductivity over the reduced Tg/T axis and also follow Debye-Stokes-Einstein relation. Therefore, despite the abrupt change in conductivity near the critical uptake (29 wt %), both cluster Tg and segmental motion remain the key factors for the ionic conduction in these EMI-Tf swollen membranes.

Original languageEnglish (US)
Pages (from-to)1273-1280
Number of pages8
JournalJournal of Polymer Science, Part B: Polymer Physics
Volume53
Issue number18
DOIs
StatePublished - Sep 15 2015

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Polymers and Plastics
  • Materials Chemistry

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