Membrane self‐diffusion coefficients for sodium ion, cesium ion, and water have been measured for Nafion® 120 perfluorosulfonate ion exchange membranes. Values have been determined as a function of temperature, and as a function of membrane water content by studying samples in heteroionic forms. The diffusional properties of this polymer are found to differ from those of conventional polystyrenesulfonates in several respects, and the free volume theory which describes ionic diffusion in the latter is inappropriate to treat Nafion. Results indicate that cations may exist in two distinct regions in the polymer; the proportion of total cations in each region may depend on the ions size and charge density. A structural model of Nafion, which correlates the membrane's spectroscopic and diffusional properties, is proposed to explain the results.

may be possible to predict the extent of stacking of purines and pyrimidines in aqueous solutions from retention data. Futher work is now being carried out to examine these postulations.

an experienced technician to obtain reliable results using the Methylene Blue Method.The results from Table III indicate that chloride ion may be included as part of the precipitate, leading to a positive error.Chloride has also been reported to give a positive error with the Methylene Blue Method (4, 18). The interference of chloride on the results of surfactant analyses using quaternary ammonium salts needs further investigation. ACKNOWLEDGMENT The authors thank M. W. Listen for testing many of the electrodes and C. A. Pearson for the Methylene Blue data. LITERATURE CITED(1) C.

Tracer self-diffusion coefficients for Na+ and Cs+ have been measured in Nation perfluorosulfonate ion-exchange membranes for three solvent systems: water, methanol, and acetonitrile. Results indicate that ion clustering exerts a pronounced effect on the diffusional properties of this material. Diffusion coefficients and activation energies of diffusion vary dramatically for small changes in swelling. This is attributed to changes in the ability of counterions to move between clusters. The ionic transport properties of Nation are therefore very different from poly(styrenesulfonate) ion-exchange resins of similar swelling.

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