Use of Microelectrode Arrays to Determine Concentration Profiles of Redox Centers in Polymer-Films
by Fritschfaules, I.; Faulkner, L. R.
Electrochemically-generated concentration profiles of redox molecules bound in a polymer film were experimentally determined by using microfabricated arrays of Au band microelectrodes in an open-face sandwich configuration. The concentration profiles should deviate from linearity if charge and mass transport are influenced by oxidation-state-dependent morphologies or by migration in the motion-restrictive medium. A thin film of methyl-quaternized poly(4-vinylpyridine) (QPVP, ca. 5000 angstrom thick) containing electrostatically-bound Fe(CN)6(3-/4-) coated the array, which was immersed in either KNO3 or potassium p-toluenesulfonate (KOTs) aqueous electrolyte. Two flanking electrodes (50-mu-m X 2 mm and 188-mu-m apart) of the array established a steady-stale concentration gradient, because one was held at an oxidizing, and the other at a reducing, potential. Fifteen smaller electrodes (4-mu-m X 2 mm and 8-mu-m apart) potentiometrically probed the intermediate chemical environment. The measured potentials were translated into the relative concentrations of the oxidized and reduced species in the film via calibration curves established in the immediately following companion paper. Concentration profiles in the QPVP/Fe(CN)6(3-/4-) system were linear, in spite of known changes in film fluidity with the state of oxidation. The communication across the array takes place by a combination of physical diffusion of redox species through the film, differential partitioning between film and solution, and diffusion through the solution. The transport is dominated by diffusion through solution, since stirring causes the concentration profiles to deviate from linearity.
- Journal
- Analytical Chemistry
- Volume
- 64
- Issue
- 10
- Year
- 1992
- Start Page
- 1118-1127
- URL
- https://dx.doi.org/10.1021/ac00034a009
- ISBN/ISSN
- 1520-6882; 0003-2700
- DOI
- 10.1021/ac00034a009