Influence of Electrostatic Interactions on Chain Dynamics and Morphological Development in Perfluorosulfonate Ionomer Membranes

 

Kirt A. Page1* and Robert B. Moore2

 

1Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD 20899

2The University of Southern Mississippi, Department of Polymer Science, Hattiesburg, MS 39406

 

Several high temperature methods of processing Nafion have been developed using various alkylammonium counterion forms of the ionomer, which has been shown to have a significant effect on the thermal and mechanical properties of this material. In particular, it has been shown that neutralization gives rise to two high-temperature mechanical relaxations. While several studies in the literature have attempted to explain the molecular origins of these mechanical relaxations, the assignments were based primarily on limited dynamic mechanical analysis (DMA) results and have at times been contradictory. The study presented here is a fundamental investigation into the molecular origins of the thermal transitions and dynamic mechanical relaxations of Nafion membranes as studied by differential scanning calorimetry (DSC), DMA, variable temperature small-angle x-ray scattering (SAXS) and solid-state 19F NMR spectroscopy. Molecular level information from NMR investigations, along with SAXS data, have led to the development of a more detailed description of the dynamics of Nafion and the molecular origins of the mechanical relaxations. These data support the assignment of the b relaxation to the genuine Tg of Nafion and the a relaxation to the onset of long-range mobility of chains/side-chains via a thermally activated destabilization of the electrostatic network. This information is a key part of understanding how the strength of electrostatic interactions in ionomers affects the chain dynamics and developing morphology in these materials.

 

Kirt A. Page

NRC Postdoctoral Fellow
Multivariant Measurement Methods Group

Polymers Division, MSEL

National Institute of Standards and Technology

Bldg. 224/Room B220
100 Bureau Drive MS8542
Gaithersburg, MD  20899-8540
Telephone:  301-975-5030
Fax:  301-975-4924

Non-member

Materials

Mentor: Michael J. Fasolka