Perfluorinated ionic polymers

The use of perfluorinated ionic polymer membranes to separate the catholyte and anolyte compartments in chloroalkali cells has been growing in importance over the past 25 years as these units have replaced the older Castner-Kellncr cells which depend upon large quantities of toxic mercury for their operation. The first perfluorinated ionic polymer, Nafion , was developed by Du Pont and was manufactured by the copolymerization of tetrafluoroethene with monomer 2. 

Since an IPMC functions as a pathway for hydrated cations, its properties will be expected to affect the performance of an IPMC actuator. The membrane materials used in IPMCs have so far been limited to a few commercially available perfluorinated ionic polymers, such as Nafion, and the thickness of the IPMC has also been restricted to the available thickness of the commercial membrane [67]. However, IPMC actuators employing new ionic membranes have now been reported [68]. The membranes are prepared from fluoropolymers grafted with polystyrene sulfonic acid (PSSA). IPMCs assembled with these membranes have been shown to exhibit at least several times larger displacements than the Nafion-based IPMC with similar thickness. 

Typically, the tip of the perfluorinated ionic polymer strip bends toward the anode (in case of cation exchange membranes) under the influence of an electric potential. Also, the appearance of water on the surface of the expansion side and the disappearance of water on the contraction side occurs near the electrodes. 

Perfluorinated Ionic Polymers for PEFCs (Including Supported PFSA)... 

Yoshitake M, Watakabe A (2008) Perfluorinated ionic polymers for PEFCs (including supported PFSA). Adv Polym Sci, Fuel Cells I 215 127-155... 

In a previous work, Kim and Shahinpoor [11] have reported a newly developed fabrication method that can scale up or down the IPMNC artificial muscles in a strip size of micro-to-centi-meter thickness, using the liquid form of perfluorinated ionic polymers. By meticulously evaporating the solvent (isopropyl alcohol) out of the solution, recast ionic polymer can be obtained. A number of these samples are shown in Figure 7.3. 

Hydration of the perfluorinated ionic polymers (PIPs) depends on the ionie form and ion-exchange eapacity (Asaka et al. 2001). In the case of the Nation membrane, the water content decreases with the increase in the hydrophobicity of the counter cation. The ionic conductivity also depends on the ionic size, the hydration, the charge density of the ionic polymer, etc. For instance, the alkali cation-form and alkaline earth cation-form PIPs have larger conductivity than alkyl ammonium cation-form PIPs. Increasing the size of the alkyl ammonium cation decreases the conductivity. These results are closely related on the ion-cluster structure of the PIP. 

The perfluorinated ionic polymers are still the best ionic polymers for the IPMC. However, these polymers have some limitations, especially their high cost for appUcations. Therefore, recently, various hydrocarbon-based ionic polymers for the IPMC have been developed (Jo et al. 2013). 

Yoshitake, M. and Watakabe, A., Perfluorinated ionic polymers for PEPCs (including supported PFSA), in Fuel Cell Handbook-I, Ed. Scherer, G.G., Advances in Polymer Science, Vol. 215, Springer-Verlag, Berlin, Germany, 2008, pp. 127-155. 

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