Diffusion Coefficients in Swelling Polypyrrole: ESCR and Cottrell Models
Reliable diffusion coefficients, D, for the diffusion of perchlorate anions into polypyrrole films during polymeric oxidation were obtained from chronoamperometric results. Two different models were used to calculate D: the Cottrell equation and the electrochemically stimulated conformational relax...
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Published in | The journal of physical chemistry. B Vol. 109; no. 5; pp. 1723 - 1729 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
10.02.2005
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Online Access | Get full text |
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Summary: | Reliable diffusion coefficients, D, for the diffusion of perchlorate anions into polypyrrole films during polymeric oxidation were obtained from chronoamperometric results. Two different models were used to calculate D: the Cottrell equation and the electrochemically stimulated conformational relaxation (ESCR) model. As expected, the initial Cottrell hypothesis was far from swelling/shrinking polymeric electrodes and the obtained D range was from 10-10 to 10-6 cm2 s-1. The ESCR model, based on the internal diffusion that takes place from regions where the steady state of oxidation has already been reached to regions where the oxidation is only just beginning, provided values of D ranging from 0.4 × 10-9 to 2.2 × 10-9 cm2 s-1, which is close to the values expected for a gel. When a constant amplitude is kept for the potential step, D increases with increasing initial anodic potentials, i.e., from increasingly swollen films. When it is stepped to the same oxidation potential, D decreases when starting from more cathodic potentials, i.e., from a more compact structure. These changes in D can be attributed to (i) swelling processes during oxidation, giving a gel-like structure; (ii) compacting processes at increasing cathodic potentials; (iii) the increasing thickness of the film during oxidation; and (iv) a decrease in film viscosity during the swelling process. |
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Bibliography: | This paper is dedicated to Prof. Cecilia Sarasola. istex:56498569B377CB92B83AA436B6E26E716BA9A4F1 ark:/67375/TPS-LDL2TZCX-M ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1520-6106 1520-5207 |
DOI: | 10.1021/jp046051q |