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Thermodynamic Considerations

Part of the Monographs in Electrochemistry book series (MOEC)

Abstract

Polymer-modified (film) electrodes currently attract the most interest from electrochemists. In these, the conducting polymer is deposited on the surface of a substrate, which is usually a metal, and investigated or used in contact with an electrolyte solution which does not contain the polymer. Clearly an equilibrium (adsorption equilibrium) will not exist between the surface phase and the solution with respect to the polymer. The adsorption model of de Gennes provides a description of this situation. Although the individual energy contribution from a segment of the polymer is small, the overall energy is large, since the small energy contributions add up. An important consequence of this metastable adsorption is that the density of the polymer layer is usually not uniform. A true equilibrium situation is seldom established for polymeric systems within the time-scale of the experiments, since the relaxation process of the polymer network (gel) can be extremely long. This is true not only with respect to polymer morphology (conformation), but also membrane equilibria (in which ions and solvent molecules participate). The surface polymer layer will be treated as an amorphous swollen gel with a uniform structure and density in contact with a solution containing solvent molecules and ions. In this case, both nonosmotic and osmotic membrane equilibria, as well as the mechanical work done in swelling the polymer, must be taken into account. In most cases the situation is even more complicated than that usually treated by a membrane equilibrium, since the charge in the polymer changes during the redox reaction; in most cases a neutral polymer is transformed into a polyelectrolyte, and vice versa.

Keywords: Thermodynamics - Partitioning equilibria - Neutral polymer in contact with an electrolyte solution - Charged polymer in contact with an electrolyte solution - Nonosmotic membrane equilibrium - Osmotic membrane equilibrium - Electrochemical and mechanical equilibria - Dimerization, disproportionation and ion association equilibria within the polymer phase

Keywords

Solvent Molecule Partial Molar Volume Polymer Phase Thermodynamic Consideration Redox Transformation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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© Springer-Verlag Berlin Heidelberg 2008

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