Nafion molecular organization

Considerable progress has been made in the solution theory of poly-electrolytes. However, for the condensed-phase analogs of polyelectrolytes, ionomers, this is not the case. Eisenberg (1) has put forth an initial theory of ionomer structure that contains conceptual formalisms of general use. His theory has been consulted extensively in the work reported here. Ponomarev and Ionova (2) have attempted to construct a sophisticated statistical mechanical model to describe the thermodynamics of ionomers. Recently, Gierke (3) has described a theory of ion transport in the Nafion ionomer based on a specific molecular organization. 

In Figures 4a-4d are representations of the molecular organization of the dry and hydrated structures for Nafion as postulated in the theory. 

Among the many classes of microreactor which have been used in organic phototransformation, we will limit our discussion only on molecular-sieve zeolites, Nafion membranes, vesicles, and low-density polyethylene films. 

Hopfinger and Mauritz and Hopfinger also presented a general formalism to describe the structural organization of Nafion membranes under different physicochemical conditions. It was assumed that ionic clustering does not exist in the dry polymer. This assumption is applicable to the perfluorinated carboxylic acid polymer" but not the perfluorosulfonate polymers." They consider the balance in energy between the elastic deformation of the matrix and the various molecular interactions that exist in the polymer. 

A general formalism is presented to describe the structural organization of ionomers under different physicochemical conditions. The theory is applied specifically to Nafion. Resultant predicted properties are compared with experimental findings. Preliminary application of the predicted ionomeric molecular structure of Nafion to modeling ion transport through Nafion chlor-alkali separators is discussed and evaluated. 

The separations listed in Table HI result from a combination of differences in solubility and diffusivity. A difference in physical solubility of benzene derivatives would be expected and is observed. In general, as the substituted side chain on benzene becomes longer its solubility in water is reduced due to its more organic nature. Therefore, if the separation was based solely on the differences in solubility, the order of decreasing flux values would be benzene > toluene > ethylbenzene > cumene. A difference in diffusion coefficients of the benzene derivatives would also be expected. In general, diffusion coefficients decrease as molecular size increases. Therefore, the order of decreasing diffusivity would be benzene > toluene > ethylbenzene > cumene. Both physical properties predict the trends seen for Na+-Nafion membranes. While incorporation of Ag+ ions into the... 

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