Substrate-Dependent Physical Aging of Confined Nafion Thin Films

Douglas I. Kushner, Michael Anthony Hickner

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The humidity-induced physical aging, or structural relaxation, of spin-cast Nafion thin films on gold, carbon, and native oxide silicon (n-SiO2) substrates was examined using spectroscopic ellipsometry (SE). Physical aging rates, β, were calculated from the change in measured sample thickness, h, upon exposure to controlled humidity. Three Nafion films, h = 188, 57, and 27 nm, deposited on gold substrates demonstrated an increased β with decreasing thickness due to confinement. The Nafion film on n-SiO2, h = 165 nm, also showed a humidity-induced aging, while a Nafion film deposited on carbon, h = 190 nm, exhibited no measurable humidity-induced aging. The reported rate of aging was related to the strength of the polymer/substrate interactions during film formation. Strong interactions between Nafion and the gold and n-SiO2 substrates anchored the thin film to the substrate during film formation, resulting in a nonequilibrium as-cast film and subsequent relaxation upon exposure to water vapor until complete plasticization. Weak interactions between the carbon substrate and Nafion resulted in fully relaxed as-cast films which displayed no relaxation upon hydration.

Original languageEnglish (US)
Pages (from-to)223-227
Number of pages5
JournalACS Macro Letters
Volume7
Issue number2
DOIs
StatePublished - Feb 20 2018

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Aging of materials
Thin films
Substrates
Atmospheric humidity
Gold
Carbon
Structural relaxation
Spectroscopic ellipsometry
Silicon oxides
Steam
perfluorosulfonic acid
Hydration
Water vapor
Polymers

All Science Journal Classification (ASJC) codes

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

Cite this

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abstract = "The humidity-induced physical aging, or structural relaxation, of spin-cast Nafion thin films on gold, carbon, and native oxide silicon (n-SiO2) substrates was examined using spectroscopic ellipsometry (SE). Physical aging rates, β, were calculated from the change in measured sample thickness, h, upon exposure to controlled humidity. Three Nafion films, h = 188, 57, and 27 nm, deposited on gold substrates demonstrated an increased β with decreasing thickness due to confinement. The Nafion film on n-SiO2, h = 165 nm, also showed a humidity-induced aging, while a Nafion film deposited on carbon, h = 190 nm, exhibited no measurable humidity-induced aging. The reported rate of aging was related to the strength of the polymer/substrate interactions during film formation. Strong interactions between Nafion and the gold and n-SiO2 substrates anchored the thin film to the substrate during film formation, resulting in a nonequilibrium as-cast film and subsequent relaxation upon exposure to water vapor until complete plasticization. Weak interactions between the carbon substrate and Nafion resulted in fully relaxed as-cast films which displayed no relaxation upon hydration.",
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Substrate-Dependent Physical Aging of Confined Nafion Thin Films. / Kushner, Douglas I.; Hickner, Michael Anthony.

In: ACS Macro Letters, Vol. 7, No. 2, 20.02.2018, p. 223-227.

Research output: Contribution to journalArticle

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