Electroactive polymer redox switching

Our goal is to develop a method for visualizing extremely complicated electroactive polymer film redox switching mechanisms. To exemplify the problem and our proposed solution, we discuss the mechanisms of two... 

First we review processes that ordinarily accompany the redox switching of an electroactive polymer. The key step is coupled electron/ion transfer, which converts one or more reduced forms of the polymer to one or more oxidized forms of the polymer. Solvent and neutral species transfers and polymer structural changes (reconfigurations or coordination state changes) accompany the switching process under permselective conditions. Under nonpermselective conditions, salt transfer also occurs [12]. 

A key issue in the redox switching of electroactive polymers relates to the value of the potential at which coupled electron/ion transfer occurs. The importance of this issue is illustrated in Fig. 13.3. The six cubes in... 

The electrochemical quartz crystal microbalance is a versatile technique for studying several aspects of electroactive polymer film dynamics. For rigid films, it is a sensitive probe of mobile species (ion and solvent) population changes within the film in response to redox switching. For non-rigid films, it can be used to determine film shear moduli. In the former case, one simply follows changes in crystal resonant frequency. In the latter case, the frequency dependence of resonator admittance in the... 

These contain redox-active centers able to switch on/off cation or anion complexation when treated with redox reagents or electrochemical stimulation. Examples include some ferrocenyl-containing macrocycles, such as (159), or donors with an anthraquinone fragment, as in (160).252 The functionalization of electroactive polymers by monocyclic polyethers has been used for the building of cation-responsive electrodes. 

One of the most widely studied electroactive polymer film systems is polyvinylfer-rocene (PVF). PVF films can be deposited by electroprecipitation from organic solvents (as discussed below) then studied as surface-immobilized films in aqueous media. Redox switching between the two ferrocene (Fc) states can be represented as a Pc+/o... 

FIGURE 12.9 Schematic illustration of chemical and biological sensor configurations involving the use of conducting electroactive polymers in redox switches. (Reprinted from Guiseppi-Elie, A., Wallace, G.G., and Matsue, T., Handbook of Conducting Polymers Marcel Dekker, New York, 1998. With permission.)... 

The redox properties of the conducting polymer film are the primary interest of the present chapter, because most of the important applications are associated with switching the electroactive polymer films from the neutral (reduced) state of the doped (oxidized) state. The voltage range in which representative polymers show electroactivity is shown in Figure 2.2, compared with inorganic materials. Li metal is chosen as the reference because of the interest in using the intercalation materials in lithium battery systems. 

Redox Switching Revisited Solvent, Salt, and Ion Transport in Electroactive Polymer Films... 

From the examples presented we see that the EQCM technique can yield quite a bit of information on the redox-switching process in an electroactive polymer film. We now discuss a diagnostic scheme proposed by Hillman and Bruckenstein, which uses combined... 

FIGURE 1.43. Hillman-Bruckenstein diagnostic flow chart (in terms of the integral quantities Q, AM, and 4>) for evaluating the rate-determining process in redox switching in electroactive polymer films. 

We end this section with a discussion of the interrelationship between mobile species transport and polymer relaxational processes in permselective electroactive polymer films when the latter undergo redox switching. This discussion is based to a large extent on a paper recently presented by Hillman and Bruckenstein. " ... 

FIGURE 1.44. A two-dimensional (1 X 1) square scheme representation of electron/ion (X) and solvent transfer (Y) processes that operate during redox switching in an electroactive polymer film. 

The peak width in the voltammetric profile conveys useful information about the electrochemistry of redox switching in an electroactive polymer film. Theory developed in Section 2.3, assuming an ideal situation of zero interredox center interaction, and sites in the layer at equilibrium with the potential applied at support electrode surface (which means that the site oxidation is Nemstian), predicts that the peak width at half height S has the following value ... 

J.-D. Stenger-Smith, J. R. Reynolds, B. Sankaran, L. H. Warren, H. O. Marcy, and G. Bauerle. 1995. Solid-state electroactive devices based on redox switching polymers. Proceedings ofSPIE-The International Society for Optical Engineering (C ical and Photonic Applications of Electroactive and Conducting Polymers) 2528 162-168. 

In this chapter, the application of this technique to the thin film processing of electroactive polymers is discussed. The fabrication of controlled molecular assemblies of electroactive polymers provides a unique opportunity to investigate the structure-property and structure-function relationships of multilayer thin films containing electrically conductive, optically nonlinear and redox active polymers. These assemblies can also be coupled to appropriate solid supports for application in such molecular electronic devices as ultrathin electrodes and transistors, opticd waveguides and switches, and chemical and biochemical microelectronic sensors. 

Tedim J, Freire C, Hillman AR (2009) Modulation of electroactive polymer film dynamics by metal ion complexation and redox switching. Soft Matter 5 2603-2613... 

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