Pt-supported SPEEK (sulfonated poly(ether ether ketone)) thin films, mimicking the ionomer–electrode interface in polymer electrolyte fuel cells (PEFCs), were synthesized with thicknesses from 12 to 105 nm. Their glass transition temperature (T_g) was analyzed via in situ thermal ellipsometry, revealing a thickness-dependent decrease in T_g, indicative of confinement effects. Particularly, a 30 nm film, typical of practical ionomer films, exhibited surface crystallization preceding that at the buried interface, a phenomenon linked to higher mobility at the free surface, as confirmed by grazing incidence wide-angle X-ray scattering (GIWAXS) at both subcritical (0.09°) and supercritical (0.14°) angles. This study elucidates the dynamic interplay between the high-mobility-free surface and the interaction-intensive buried interface in confined SPEEK thin films. It was observed that below 30 nm thickness, interfacial interactions become the primary factor influencing transition temperature. Additionally, spatially heterogeneous crystallization, more pronounced in the out-of-plane direction, correlates with reduced proton conduction, underscoring the impact of membrane electrolyte assembly (MEA) hot-pressing on the functional properties of Nafion alternatives.

中文翻译：

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拓扑约束 SPEEK 薄膜的退火诱导异质结晶

合成了厚度为 12 至 105 nm 的 Pt 支撑 SPEEK（磺化聚醚醚酮）薄膜，模拟聚合物电解质燃料电池 (PEFC) 中的离聚物 - 电极界面。通过原位热椭圆光度法分析它们的玻璃化转变温度（T _{g ），揭示了}T _g随厚度的降低，这表明了限制效应。特别是，典型的实用离聚物薄膜 30 nm 薄膜在埋入界面处表现出表面结晶，这种现象与自由表面的较高迁移率有关，这一点通过掠入射广角 X 射线散射 (GIWAXS) 证实。亚临界 (0.09°) 和超临界 (0.14°) 角度。这项研究阐明了受限 SPEEK 薄膜中高迁移率自由表面和相互作用密集的埋入界面之间的动态相互作用。据观察，厚度低于30 nm时，界面相互作用成为影响转变温度的主要因素。此外，空间异质结晶（在面外方向更为明显）与质子传导降低相关，强调了膜电解质组件（MEA）热压对 Nafion 替代品功能特性的影响。