TY - JOUR
T1 - Substrate-Dependent Physical Aging of Confined Nafion Thin Films
AU - Kushner, Douglas I.
AU - Hickner, Michael A.
N1 - Funding Information:
The authors acknowledge the support of the US Department of Energy, the Office of Energy Efficiency and Renewable Energy, the Fuel Cells Technology Program through a subcontract from General Motors Corporation under grant DE-EE0000470. Additional support for this work was provided by the Office of Naval Research, Grant N00014-10-1-0875. Infrastructure support was provided by The Pennsylvania State University Materials Research Institute and the Institutes of Energy & the Environment. M.A.H. acknowledges the Corning Foundation and the Corning Faculty Fellowship in Materials Science and Engineering for support.
Publisher Copyright:
© 2018 American Chemical Society.
PY - 2018/2/20
Y1 - 2018/2/20
N2 - 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.
AB - 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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U2 - 10.1021/acsmacrolett.7b01004
DO - 10.1021/acsmacrolett.7b01004
M3 - Article
C2 - 35610897
AN - SCOPUS:85042348861
SN - 2161-1653
VL - 7
SP - 223
EP - 227
JO - ACS Macro Letters
JF - ACS Macro Letters
IS - 2
ER -