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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Development of membrane chlor‐alkali cells during this past decade represents a major advancement for commercial electrochemical technology. Chemical engineering applications of separation processes such as this involve diffusional mass transfer that can be treated as a rate process. The chlor‐alkali application includes sodium, chloride, and hydroxyl ions plus water as mobile species in caustic soda and brine solutions and also between immiscible membrane and solution phases. These immiscible phases are brought into contact to allow selective transfer of sodium and water from brine to the caustic solutions. Previous data reported on normalNaOH diffusion through Nafion® membranes, DnormalNaoH , are difficult to interpret because not only do they involve hydroxide and sodium ion fluxes to give average diffusion coefficients, but also unknown gradients of electrolyte and water concentration are present in the membrane phase. This present work greatly simplifies these problems encountered by isolating and measuring the precise sodium ion self‐diffusion coefficient, DnormalNa+ , with radio‐tracer techniques in various du Pont Nafion® and EDA modified membranes. It then relates the DnormalNa+ to equivalent weight, surface treatment, and fabric backing in these membranes. These data for DnormalNa+ are very important in chlor‐alkali cells because the sodium ion is the major current carrier; therefore, its value can be related to the relative activation energy and voltage drop among similar membranes.

Sodium ion, cesium ion, and water self-diffusion coefficients in a perfluorinated carboxylate polymer film have been measured. Results are compared to those obtained for a perfluorinated sulfonate polymer, Nation. Both cation and water diffusion coefficients are very large in these materials in relation to the equilibrium amounts of sorbed water. The carboxylate polymer shows larger diffusion coefficients but smaller water sorption, compared to Nation. Infrared results indicate significant changes in the state of sorbed water between the two materials. Results are discussed in terms of the ion clustered morphology of these ion exchange polymers.* Electrochemical Society Active Member.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.132.123.28 Downloaded on 2015-02-05 to IP

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