Low Temperature Water Dynamics Study in Fully Hydrated Nafion® Membrane

Previous studies of water dynamics in hydrated Nafion® film utilizing various experimental techniques resulted in several different temperatures at which the water freezes in the hydrated Nafion® membrane. The goal of this project is to gain further insights into the low temperature water dynamics in this system by using luminescent probes in addition to differential scanning calorimetry technique. The asymmetry in peaks and enthalpies of water freezing and ice melting in the DSC thermogram indicates that a portion of water freezing starts at -38 °C; about 34 wt% of water is frozen at -65 °C and water continues to freeze as the temperature decreases to -150 °C. The thermogram also reveals that the frozen water in Nafion® membrane melts at -22 °C, which is consistent with the previously established fact that the water freezing and melting temperatures are sample size dependent. The emission spectra of *Ru(bpy)32+ embedded Nafion® film were captured from room temperature to -180 °C. Three crossovers (-30, -71, -105.5 ℃) were detected in the emission spectra maximum vs. temperature plot as shown in Figure 5; the first two can be attributed to some phase transition in the polymer membrane matrix while the third one can be attributed to the complete freezing of water inside the membrane. The photophysical properties of the PRODAN luminescent probe were analyzed in water-ethanol mixtures in the temperature range +25 to -150 °C. It was concluded that PRODAN can be used as a luminescent probe sensitive to water mobility. However, an attempt to use PRODAN as a luminescent probe for water dynamics in hydrated Nafion® membrane failed because Nafion® acted as a catalyst and PRODAN was degraded.

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Work Title Low Temperature Water Dynamics Study in Fully Hydrated Nafion® Membrane
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  1. Yin-Jen Chang
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Work Type Research Paper
Publication Date 2023
Deposited December 15, 2023

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    Publication Date
    • 2023-12-15
    • 2023
  • Updated Description Show Changes
    Description
    • Previous studies of water dynamics in hydrated Nafion® film utilizing various experimental techniques resulted in several different temperatures at which the water freezes in the hydrated Nafion® membrane. The goal of this project is to gain further insights into the low temperature water dynamics in this system by using luminescent probes in addition to differential scanning calorimetry technique. The asymmetry in peaks and enthalpies of water freezing and ice melting in the DSC thermogram indicates that a portion of water freezing starts at -38 °C; about 34 wt% of water is frozen at -65 °C and water continues to freeze as the temperature decreases to -150 °C. The thermogram also reveals that the frozen water in Nafion® membrane melts at -22 °C, which is consistent with the previously established fact that the water freezing and melting temperatures are sample size dependent. The emission spectra of *Ru(bpy)32+ embedded Nafion® film were captured from room temperature to -180 °C. Three crossovers (-30, -71, -105.5 ℃) were detected in the emission spectra maximum vs. temperature plot as shown in Figure 5; the first two can be attributed to some phase transition in the polymer membrane matrix while the third one can be attributed to the complete freezing of water inside the membrane. The photophysical properties of the PRODAN luminescent probe were analyzed in water-ethanol mixtures in the temperature range +25 to -150 °C. It was concluded that PRODAN can be used as a luminescent probe sensitive to water mobility. However, an attempt to use PRODAN as a luminescent probe for water dynamics in hydrated Nafion® membrane failed because Nafion® acted as a catalyst and PRODAN was degraded.
  • Added Creator Yin-Jen Chang
  • Added LOW TEMPERATURE WATER DYNAMICS STUDY IN FULLY HYDRATED NAFION® MEMBRANE .pdf
  • Deleted LOW TEMPERATURE WATER DYNAMICS STUDY IN FULLY HYDRATED NAFION® MEMBRANE .pdf
  • Added LOW TEMPERATURE WATER DYNAMICS STUDY IN FULLY HYDRATED NAFION® MEMBRANE .pdf
  • Updated Description, License Show Changes
    Description
    • Previous studies of water dynamics in hydrated Nafion® film utilizing various experimental techniques resulted in several different temperatures at which the water freezes in the hydrated Nafion® membrane. The goal of this project is to gain further insights into the low temperature water dynamics in this system by using luminescent probes in addition to differential scanning calorimetry technique. The asymmetry in peaks and enthalpies of water freezing and ice melting in the DSC thermogram indicates that a portion of water freezing starts at -38 °C; about 34 wt% of water is frozen at -65 °C and water continues to freeze as the temperature decreases to -150 °C. The thermogram also reveals that the frozen water in Nafion® membrane melts at -22 °C, which is consistent with the previously established fact that the water freezing and melting temperatures are sample size dependent. The emission spectra of *Ru(bpy)32+ embedded Nafion® film were captured from room temperature to -180 °C. Three crossovers (-30, -71, -105.5 ℃) were detected in the emission spectra maximum vs. temperature plot as shown in Figure 5; the first two can be attributed to some phase transition in the polymer membrane matrix while the third one can be attributed to the complete freezing of water inside the membrane. The photophysical properties of the PRODAN luminescent probe were analyzed in water-ethanol mixtures in the temperature range +25 to -150 °C. It was concluded that PRODAN can be used as a luminescent probe sensitive to water mobility. However, an attempt to use PRODAN as a luminescent probe for water dynamics in hydrated Nafion® membrane failed because Nafion® acted as a catalyst and PRODAN was degraded.
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    • https://rightsstatements.org/page/InC/1.0/
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    Work Title
    • LOW TEMPERATURE WATER DYNAMICS STUDY IN FULLY HYDRATED NAFION® MEMBRANE
    • Low Temperature Water Dynamics Study in Fully Hydrated Nafion® Membrane
  • Updated