Polymers electrochemical behavior

The presence of polymer, solvent, and ionic components in conducting polymers reminds one of the composition of the materials chosen by nature to produce muscles, neurons, and skin in living creatures. We will describe here some devices ready for commercial applications, such as artificial muscles, smart windows, or smart membranes other industrial products such as polymeric batteries or smart mirrors and processes and devices under development, such as biocompatible nervous system interfaces, smart membranes, and electron-ion transducers, all of them based on the electrochemical behavior of electrodes that are three dimensional at the molecular level. During the discussion we will emphasize the analogies between these electrochemical systems and analogous biological systems. Our aim is to introduce an electrochemistry for conducting polymers, and by extension, for any electrodic process where the structure of the electrode is taken into account. 

Most of the models developed to describe the electrochemical behavior of the conducting polymers attempt an approach through porous structure, percolation thresholds between oxidized and reduced regions, and changes of phases, including nucleation processes, etc. (see Refs. 93, 94, 176, 177, and references therein). Most of them have been successful in describing some specific behavior of the system, but they fail when the... 

As illustrated in the previous sections, the electrochemical properties of conducting polymer films are strongly influenced by polymer-ion interactions. These interactions are in turn influenced by the nature of the solvent and the solvent content of the film. Consequently, the electrochemical behavior of conducting polymer films can be highly solvent dependent. Films can even become electrochemically inactive because of lack of solvation.114,197... 

ANK Lau, LL Miller. Electrochemical behavior of a dopamine polymer. Dopamine release as a primitive analogue of a synapse. J Am Chem Soc 105 5271-5277, 1983. 

The electrochemical behavior of ferrocene-based polymers [15] and of complexes containing a large, well defined number of ferrocene-type units [16] had already been reported when several groups became interested in dendrimer research. In the past few years several dendrimers of different chemical nature and structure carrying ferrocene-type units in the periphery have been synthesized... 

In this paper we describe the preparation of thin polymer films by surface catalysis and anodic deposition. The results indicate that both synthesis routes produce orientationally ordered films that have similar infrared spectra. It is also shown that thin ordered films of poly(thiophene) have different electrochemical behavior than the fibrous films that are electrically conducting. 

Electroanalytical sensors based on amperometric measurements at chemically modified electrodes are in the early stages of development. The modes of modification can take many forms, but the most common approach at the present time is the immobilization of ions and molecules in polymer films which are applied to bare metal, semiconductor, and carbon electrodes. Such surface-modified electrodes exhibit unique electrochemical behavior which has been exploited for a variety of applications. 

The electrochemical behavior of poly(ferrocenylsilanes) has been studied at three levels—in solution by cyclic voltammetry, as films deposited on electrodes, and in the solid state via iodine doping. Solution cyclic voltammetric oxidation and reduction has shown that the polymer, where R/R is Me/Me, reversibly oxidizes in methylene chloride in two stages, apparently with the first oxidation being on alternating iron atoms along the chain.29 Films cast on electrodes behave in a similar way and also show an electrochromic response to oxidation and reduction.30... 

In this paper we report the electrochemical polymerization of the PPy-GOD film on the glassy carbon (GC) electrode in enzyme solution without other supporting electrolytes and the electrochemical behavior of the synthesized PPy-GOD film electrode. Because the GOD enzyme molecules were doped into the polymer, the film electrode showed a different cyclic voltammetric behavior from that of a polypyrrole film doped with small anions. The film electrode has a good catalytic behavior to glucose, which is dependent on the film thickness and pH. The interesting result observed is that the thin PPy-GOD film electrode shows selectivity to some hydrophilic pharmaceutical drugs which may result in a new analytical application of the enzyme electrode. 

This species can be identified by its UV/Vis absorption spectrum, which in ethanol shows a Amax of 460 nm, and its very specific electrochemical behavior. Detailed electrochemical studies of this redox polymer and of mononuclear analogues have shown that two different electrochemical processes occur, both of which are pH-dependent [31]. In the first step, the Ru(ll) center is oxidized to Ru(m). Below the pKa of the Rum-H20 species of 0.85, the RuII/m couple may be described by the following equation ... 

As outlined above, the electrochemical properties of this redox species are strongly pH-dependent and this behavior can be used to illustrate the supramolecular nature of the interaction between the polymer backbone and the pendent redox center. The cyclic voltammetry data shown in Figure 4.17 are obtained at pH = 0, where the polymer has an open structure and the free pyridine units are protonated (pKa(PVP) = 3.3). The cyclic voltammograms obtained for the same experiment carried out at pH 5.7 are shown in Figure 4.18. At this pH, the polymer backbone is not protonated and upon aquation of the metal center the layer becomes redox-inactive, since protons are involved in this redox process. This interaction between the redox center and the polymer backbone is typical for these types of materials. Such an interaction is of fundamental importance for the electrochemical behavior of these layers and highlights the supramolecular principles which control the chemistry of thin films of these redox-active polymers. Finally, it is important to note that the photophysical properties of polymer films are very similar to those observed in solution. Since the layer thickness is much more than that of a monolayer, deactivation by the solid substrate is not observed. 

Polymer-modified electrodes have shown considerable utility as redox catalysts. In many cases, modified electrode surfaces show an improved electrochemical behavior towards redox species in solution, thus allowing them to be oxidized or reduced at less extreme potentials. In this manner, overpotentials can be eliminated and more selective determination of target molecules can be achieved. In this discussion, a mediated reduction process will be considered, although similar considerations can be used to discuss mediated oxidation processes. This mediation process between a surface-bound redox couple A/B and a solution-based species Y can be describes by the following ... 

The electrochemical behavior of lithium electrodes in a variety of polymeric electrolyte systems was studied extensively by a number of groups, including Scrosati et al. [390-392], Panero et al. [393], Abraham et al. [394-396], Osaka et al. [397-398], Watanabe et al. [399-401], Peled et al. [402], It is clear that there are surface reactions between the lithium and all of the polymeric systems mentioned above. It has already been clearly shown that the ether linkage is attacked by lithium, resulting in the formation of Li alkoxy species [149], Hence, it is expected the PEO-based polymers also react with Li surfaces. Spec-troelectrochemical studies of the Li-PEO system by Scherson et al. [177] provide some evidence for this possibility. Besides the polymers, the polymeric electrolyte systems contain salts with anions such as Aslv,, S03CF3, NlSOTTO),, ... 

The methods of synthesis, the spectral and photochromic properties in solution, in polymer film and in vacuum-deposited thin films, and the structural determinations by X-ray diffraction are reviewed as is the electrochemical behavior of this family of switchable materials. 

The difference in oxidation potentials (A ) detected for the two waves found for the poly(ferrocenylsilanes) 15 (R = R = Me, Et, -Bu, -Hex), which provides an indication of the degree of interaction between the iron sites, varies from 0.21 V (for 15 (R = R = Me)) to 0.29 V (for 15 (R = R = -Bu or -Hex)) (63). This indicates that the extent of the interaction between the ferrocenyl units in poly(ferrocenylsilanes) depends significantly on the nature of the substituents at silicon, which may be a result of electronic or conformational effects (63). Unsymmetrically substituted poly(ferrocenylsilanes) show similar electrochemical behavior (59). In addition, polymer 15 (R = Me, R = Fc) shows a complex cyclic voltammogram which indicates that interactions exist between the iron centers in the polymer backbone and the ferrocenyl side groups (59). 

The electrocatalytic effect (oxidation of NADH) observed with a glassy carbon electrode coated with polymer containing dopamine (covalently attached to a polymethyl methacrylic matrix) is analogous to bulk reactions of melanins (see Section V). The overall electrochemical behavior, however, indicates a very slow reaction involving only a few monolayers (250),... 

Self-doped PANI are very interesting due to their unique electrochemical behavior unlike PANI, the self-doped polymer remains in its doped state in near neutral or alkaline media [28]. Fully self-doped PANIs are not easy to synthesize due to the lower reactivity of acid-functionalized anilines. Kim et al. [29, 30] introduced an alternative approach in the template-assisted enzymatic polymerization of aniline. Previously, only polyanionic templates had been used for PANI synthesis. However, acid-functionalized anilines bear a net anionic charge in aqueous solution, and attempts to use SPS as template with carboxyl-functionalized aniline resulted in red-brown colored polymers with no polaron transitions, regardless of the synthetic conditions. The use of polycationic templates, such as those shown in Figure 8.2 allowed the synthesis of linear and electrically conductive PANIs with self-doping ability due to the doping effect of the carboxyl groups present in the polymer backbone. 

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