Nafion membranes mechanical properties

Bauer, F., Denneler, S. and Wilert-Porada, M. 2005. Influence of temperature and humidity on the mechanical properties of Nafion 117 polymer electrolyte membrane. Journal of Polymer Science Part B Polymer Physics 43 786-795. 

The mechanical properties of Nafion materials have not been of the most critical importance, as in the case of commercial thermoplastics or composite materials that are expected to be load-bearing. Rather, the primary focus has been on transport properties. To be sure, the mechanical integrity of membranes as mounted in cells, and under the perturbation of pressure gradients, swelling-dehydration cycles, mechanical creep, extreme temperatures, and the onset of brittleness and tear resistance, is important and must be taken into consideration. 

In the development of fuel-cell technology based on this unique polymer electrolyte, special chapters in electrochemical science and engineering have emerged, addressing the fuel-cell ionomeric membrane itself and the optimized fabrication of MEAs. The invention of Nafion, a poly(perfluorosulfonic acid) (poly(PFSA)) at DuPont in the 1960s, was, in fact, a key (if not the key) milestone in the development of PEFC technology. The chemical and mechanical properties of such poly(PFSA) extruded membranes, which are based on a perfluorocar-bon backbone, enabled to achieve stable materials properties and, consequently,... 

The effect of NaOH concentration on the ion transport and rheological properties of the Nafion ion exchange membranes may be attributable to some variation in the ionic domain structure in the presence of NaOH. Therefore, it is extremely Important to understand the ionic domain structure under these conditions. The anomalous behavior of Na" " ion transport as a function of NaOH concentration is seen more frequently in bilayer Nafion membranes in which one layer is treated with diamine and also in perfluorinated carboxylic ion exchange membranes. Several mechanisms have been proposed to explain their ion transport results including water absorption, transport of hydroxide ion tunneling, ion pairing mechanisms, etc. (54-56). As the ion transport properties are beyond the scope of this review, no detailed discussion will be presented. 

MWCNTs in the PFSA resin. Compared to the recast Nafion membranes, both stretching and tensile strength values were greatly improved (by 27% and 54%, respectively). A comparison ofthe mechanical properties and electronic conductivity showed the optimum MWCNT content to be approximately 3 wt%. 

The solvent and ion exchange sites in "Nafion" perfluori-nated membranes phase separate from the fluorocarbon matrix to form clusters (1-5). This ionic clustering will not only affect the mechanical properties of the polymer (JL), but should also have a direct effect on the transport properties across these membranes (2). In addition the exchange sites in the resin are strongly acidic and the polymer is extremely hydrophilic. Combined with the polymer s exceptional thermal and chemical stability, these properties make "Nafion" membranes particularly suitable for a variety of applications. These include applications as membrane separators in several electrochemical processes (6-9), as a superacid catalyst in organic syntheses (10-12), and as a membrane electrode (13). 

An appropriate amount of Nafion ionomer (5% wt/wt, Aldrich) was mixed with 3% wt/wt Si02 (Aerosil 200, Degussa) in an ultrasonic bath for 30 min. This solution was cast [19,20] in a Petri dish and heated at 80°C for 30 min. The recast composite Nafion film was detached from the Petri dish by addition of distilled water and allowed to dry for 15 hrs at room temperature. Afterwards, it was cut to obtain a regular shape and then hot pressed between two PTFE foils at a few bars and increasing temperatures. The final treatment was 160°C for 10 min. The latter step allowed to increase the crystalline fraction inside the composite membrane with consequent improvement of the mechanical properties. The... 

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