Infrared and Raman spectroscopy techniques were applied to investigate the drying and aggregation behavior of Nafion ionomer particles dispersed in aqueous solution. Gravimetric measurements aided the identification of gel-phase development within a series of time-resolved spectra that tracked transformations of a dispersion sample during solvent evaporation. A spectral band characteristic of ionomer sidechain end group vibration provided a quantitative probe of the dispersion-to-gel change. For sets of attenuated total reflection Fourier transform infrared (ATR FT-IR) spectra, adherence to Beer's law was attributed to the relatively constant refractive index in the frequency region of hydrated -SO3- group vibrations as fluorocarbon-rich ionomer regions aggregate in forming the structural framework of membranes and thin films. Although vibrational bands associated with ionomer backbone CF2 stretching vibrations were affected by distortion characteristic of wavelength-dependent refractive index change within a sample, the onset of band distortion signaled gel formation and coincided with ionomer mass % values just below the critical gelation point for Nafion aqueous dispersions. Similar temporal behavior was observed in confocal Raman microscopy experiments that monitored the formation of a thin ionomer film from an individual dispersion droplet. For the ATR FT-IR spectroscopy and confocal Raman microscopy techniques, intensity in the water H-O-H bending vibrational band dropped sharply at the ionomer critical gelation point and displayed a time dependence consistent with changes in water content derived from gravimetric measurements. The reported studies lay groundwork for examining the impact of dispersing solvents and above-ambient temperatures on fluorinated ionomer transformations that influence structural properties of dispersion-cast membranes and thin films.

中文翻译：

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EXPRESS：Nafion 离聚物分散体凝胶转变的振动光谱监测

应用红外和拉曼光谱技术研究分散在水溶液中的 Nafion 离聚物颗粒的干燥和聚集行为。重量测量有助于在一系列时间分辨光谱中识别凝胶相的发展，这些光谱跟踪溶剂蒸发过程中分散体样品的转变。离聚物侧链端基振动的光谱带特征提供了分散到凝胶变化的定量探测。对于一组衰减全反射傅里叶变换红外 (ATR FT-IR) 光谱，遵循比尔定律归因于水合 -SO3- 基团振动频率区域中相对恒定的折射率，因为富含碳氟化合物的离聚物区域在形成膜和薄膜的结构框架。尽管与离聚物骨架 CF2 伸缩振动相关的振动带受到样品内波长相关折射率变化的畸变特征的影响，但带畸变的开始标志着凝胶形成，并且与刚好低于 Nafion 水溶液临界凝胶点的离聚物质量百分比值一致分散体。在共焦拉曼显微镜实验中观察到类似的时间行为，该实验监测从单个分散液滴形成离聚物薄膜。对于 ATR FT-IR 光谱和共焦拉曼显微镜技术，水 HOH 弯曲振动带的强度在离聚物临界凝胶点处急剧下降，并显示出与从重量测量得出的水含量变化一致的时间依赖性。