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.

中文翻译：

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受限 Nafion 薄膜的基板相关物理老化

_{使用光谱椭偏仪 (SE) 检查了在金、碳和天然氧化硅 (n-SiO 2} ) 基板上旋转铸造 Nafion 薄膜的湿度引起的物理老化或结构松弛。物理老化率 β 由暴露于受控湿度时测量的样品厚度h的变化计算得出。三个 Nafion 薄膜，h = 188、57 和 27 nm，沉积在金基板上，由于限制，随着厚度的减小，β 值增加。n-SiO ₂上的 Nafion 薄膜，h = 165 nm，也显示出湿度引起的老化，而沉积在碳上的 Nafion 薄膜，h= 190 nm，没有表现出可测量的湿度引起的老化。报告的老化速率与成膜过程中聚合物/基材相互作用的强度有关。在成膜过程中，Nafion 与金和 n-SiO ₂基材之间的强相互作用将薄膜固定在基材上，导致铸态薄膜不平衡，随后在暴露于水蒸气后松弛直至完全塑化。碳底物和 Nafion 之间的弱相互作用导致完全松弛的铸态薄膜，在水合时没有表现出松弛。