Ionomer membrane systems properties

Comparison of the Properties of the Different Ionomer Membrane Systems... 

So far, CG approaches offer the most viable route to the molecular modeling of self-organization phenomena in hydrated ionomer membranes. Admittedly, the coarse-grained treatment implies simplifications in structural representation and in interactions, which can be systematically improved with advanced force-matching procedures however, it allows simulating systems with sufficient size and sufficient statishcal sampling. Structural correlations, thermodynamic properties, and transport parameters can be studied. 

The main question addressed in this review was what role do the competing interactions play for the struetural properties of hydrated ionomer membranes at low water contents. The behavior of such systems, in particular, their nanoscale organization, is dictated by the relative strength of the competing hydrophobic/polar interactions and can be tuned by varying parameters such as temperature, hydration level, and molecular architecture. 

The ionic groups, although present in small amoimts, dominate the viscoelastic behavior of ionomers, their transport properties and their ability to sorb a variety of solvents moreover, the ion effect is specific. In terms of morphology, the presence of ions leads to microphase separation into ionic and nonpolar domains. Increasing interest in structural aspects of ionomers is closely related to their numerous applications as bulk materials, in various devices, as catalysts, in controlled release systems, and as proton exchange membranes (PEM) in fuel cells (71). 

The studies described in this paper were designed to use the special properties of ionomers, but they are not the only type of chemistry that does so. Other chemical systems that employ ionomer properties include their use as sources of protons of high effective acidity (superacidity) in the catalysis of organic reactions (9-11) and then-use as integral components of chemically active membranes (e.g. cell dividers or electrode coatings) (12). 

The interactions of various polar agents with the ionic groups and the ensuing property changes are unique to ionomer systems. This plasticization process is also important in membrane applications. A different application of ionic cluster plasticization involves the interaction of metal stearates to induce softening transitions. The plasticization process is required to achieve the processability of TPEs based on this technology. 

Optimization of the electrodes for these fuel cell systems has just started. Work has been done on the optimization of electrode structure for operation under hot, dry conditions, but less has been done to study catalysis under these conditions. Part of the reason for this is that as stated above there are no commercially available polymeric materials available for the development of new electrodes studies. It is hoped that until commercially available materials for this application become available that researchers offer to share their materials. This will, however, be insufficient as the ionomers developed for catalyst layers need different properties than ionomers developed to act as fuel cell membranes. The other major issue is that catalysts for fuel cells mn under conditions of water saturation have been developed using liquid phase electrochemical methods. It will be extremely important that new catalyst for fuel cells to be operated under hot, dry conditions be developed by solid-state electrochemistry. New methods must also be developed so that electrodes containing compatible ionomers can be tested. 

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