Document Type

Dissertation

Date of Award

1974

Keywords

Ion exchange, Alkali metal ions, Chemical kinetics

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Bruce McDuffie

Second Advisor

John J. Eisch

Third Advisor

Michael E. Hargok

Abstract

Rates of alkali metal cation self-diffusion in a polystyrene sulfonate ion exchange resin and in the external solution have been measured over a range of dimethyl sulfoxide (DMSO)-water mixtures from 0 to 70 mole % DMSO. Interpretation of results is simplified by the choice of this system which exhibits relatively constant resin swelling, fairly high dielectric constant and virtually no solvent preference over the entire composition range.

The self-diffusion coefficient of Na+ in the external solution shows a moderate decrease from 0 to about 40 mole % DMSO after which it tends to level off with increasing DMSO. In the resin, however, the effective Na+ self-diffusion coefficient drops by several orders of magnitude with increasing DMSO from 0 to 70 mole %.

It is suggested that the explanation for these data lies in the strong affinity of DMSO for water and the 1:2 complex formed between the two solvents. As the DMSO content is increased to the 33 mole % level, the sodium ion is increasingly unable to fulfill its solvation requirements. In the external solution this results in a rate of diffusion greater than might be expected from the increase in viscosity. In the resin, however, the result is an increasing tendency to ion association and a resultant decrease in the effective diffusion coefficient. Above the 33 mole % DMSO level, ion association is increasingly favored by lack of water to solvate the fixed anions, and, at the highest DMSO levels studied, by insufficient amounts of any solvent to meet the solvation requirements of either cation or anion.

Activation energy for diffusion data are consistent with this explanation which is also supported by data for self-diffusion of the rubidium ion.

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