Ionomer perfluorinated, solution

Fig. 19.11. Model of rod-like structure of perfluorinated ionomer in solution (from Ref. [67])...

Industrial applications of perfluorinated ionomer membranes such as the electrolysis of sodium chloride solution to produce chlorine and sodium hydroxide often involve the use of highly concentrated solutions at elevated temperatures. The optimization of these systems depends upon a sound characterization of membrane transport processes under such conditions. Sodium ion is the major current-carrying species through the membrane in a chlor-alkali cell, and... 

Figure 12. Activation energy of Na diffusion in perfluorinated ionomer membranes vs. NaOH solution concentration, 70-90°C temperature interval. (Ref. 168 reprinted by permission of the publisher, The Electrochemical Society, Inc.)...

These performance goals have now largely been attained by continued improvements through several generations of materials. Currently, commercial perfluorinated ionomer materials for this application consist of membranes with carboxylate or mixed carboxylate-sulfonate functionality the latter membranes often have layered structures with the carboxylate layer exposed to the caustic catholyte solution. Fabric reinforcement is used in some instances to improve strength. 

The very high values of t ja+ (approaching 0.98 under certain conditions) and its variation with changes in cell parameters are subjects of great theoretical and practical interest. It should be noted that the lack of hydroxide ion migration through the membrane is not due to a Donnan exclusion process considerable sorption of NaOH is found in these perfluorinated ionomer membranes when they are exposed to caustic solutions (5). 

Cirkel, F A., Okada, T., and Kinugasa, S. 1999. Equilibrium aggregation in perfluorinated ionomer solutions. Macromolecules 32 531-533. 

Althongh perfluorinated or partially fluorinated ionomers are mostly favored as fuel cell membrane materials due to their unique resistance to chemical attack from their surroundings, fundamental solution to overcome inherent shortcomings of Nafion and other fluorinated membranes would be the development of chemically different types of ionomers. Alternative membranes for PFS A can reduce methanol crossover as low as two orders of magnitude. Such membranes are discussed in the following sections. 

For almost ten years the properties of ionomer solutions have been studied and lightly sulfonated polystyrene (S-PS) was chosen as the model compound. The properties of S-PS ionomer solutions in polar and nonpolar solvents, which are briefly reviewed, were associated with polyelectrolyte and ionomer behavior respectively. In both cases, structural models have been proposed to explain the rheological and scattering data. A similar study on perfluorinated ionomer solutions is then presented and compared in order to define some general ionomer behavior. 

Fig. 19.10. Extended Guinier plot of a dilute perfluorinated ionomer solution in N-methylformam-ide with and without added salt (from Ref. [69])...

Yang, L., Li, H., Ai, F., Chen, X., Tang, J., Zhu, Y, Wang, C., Yuan, W.Z., Zhang, Y, and Zhang, Y. (2013) A new method to prepare high performance fluorinated sulfonic acid ionomer/porous expanded polytetrafluoroethylene composite membranes based on perfluorinated suHonyl fluoride polymer solution, J. Power Sourc., 243, 392-396. 

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