Vibrational Spectroscopic Monitoring of the Gelation Transition in Nafion Ionomer Dispersions

Journal Article · Thu Jul 23 00:00:00 EDT 2020 · Applied Spectroscopy

DOI:https://doi.org/10.1177/0003702820949129· OSTI ID:2473703

Liang, Ying ^[1]; Kitt, Jay P. ^[2]; Minteer, Shelley D. ^[2]; Harris, Joel M. ^[2]; Korzeniewski, Carol ^[3]

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1. Texas Tech University, Lubbock, TX (United States); University of Utah
2. University of Utah, Salt Lake City, UT (United States)
3. Texas Tech University, Lubbock, TX (United States); University of Utah, Salt Lake City, UT (United States)

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 –SO$$^{–}_{3}$$ 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.

• Research Organization: University of Utah, Salt Lake City, UT (United States)
• Sponsoring Organization: U.S. National Science Foundation; USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: FG03-93ER14333
• OSTI ID: 2473703
• Alternate ID(s): OSTI ID: 2480559
• Journal Information: Applied Spectroscopy, Journal Name: Applied Spectroscopy Journal Issue: 4 Vol. 75; ISSN 0003-7028
• Publisher: Society for Applied Spectroscopy
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ATR-IR
Infrared spectroscopy
Nafion
Raman spectroscopy
attenuated total reflection infrared
ionomer thin films
polymers