Conductive Electroactive Polymers mechanism

Conductivity within conducting electroactive polymers (CEPs) is a complex issue. A polymer that can exhibit conductivity across a range of some 15 orders of magnitude most likely utilizes different mechanisms under different conditions. In addition to the electronic conductivity exhibited by CEPs, they possess ionic conductivity because of the solvent or electrolyte incorporated during synthesis. The experimental parameters encountered during synthesis (as listed and discussed in Chapter 2) have an effect on the polymer conductivity. In particular, the electrochemical conditions, the solvent, the counterion, and monomers used during synthesis influence the electronic properties of the resulting polymer. 

As with polypyrrole (PPy), the electrical, chemical, and mechanical properties of polyaniline (PAn) are inextricably linked. In addition, PAn has spectacular optical and chromic properties that distinguish it from other conducting electroactive polymers (CEPs). The current state of knowledge concerning properties of PAn is reviewed in this chapter. 

A general approach to fabricating solid-state ion-selective microelectrodes has been described whereby a conducting electroactive polymer, which is both an electronic and an ionic conductor (e.g., polypyrrole, polythiophene, or polyaniline), is used to mediate charge exchange between an ion-selective membrane (an ion conductor) and a metal substrate (an electronic conductor) [28]. These electrodes are reported to be robust and mechanically flexible while exhibiting good potential stability with no redox sensitivity. While applications to potentiometric SECM have been described [28], these electrodes have yet to find use in corrosion studies. 

Refs. [i] Chance RR, Boundreaux DS, Bredas J-L, Silbey R (1986) Solitons, polarons and bipolarons in conjugated polymers. In Skotheim TA (Ed) Handbook of conducting polymers, vol. 2, Marcel Dekker, p 825 [ii] Inzelt G (1994) Mechanism of charge transport in polymer-modified electrodes. In Bard AJ (Ed) Electroanalytical chemistry, vol. 18, Marcel Dekker [iii] Lyons MEG (1994) Charge percolation in electroactive polymers. In Lyons MEG (ed) Electroactive polymer electrochemistry, Parti, Plenum, New York, p 1... 

Components with improved mechanical properties can be produced by mixing the above processable polymers with other polymers. For example, we have mixed conducting polymer colloids with water based latex paints to form conductive, electroactive paints with excellent adhesion to a range of metals [132], Interestingly, the paint-metal adhesion was actually increased by addition of the conducting polymer colloid. 

Intercalation of electroactive polymers such as polyaniline and polypyrrole in mica-type layered silicates leads to metal-insulator nanocomposites. The conductivity of these nanocomposites in the form of films is highly anisotropic, with the in-plane conductivity 10 to 10 times higher than the conductivity in the direction perpendicular to the film. Conductive polymer/oxide bronze nanocomposites have been prepared by intercalating polythiophene in V2O5 layered phase, which is analogous to clays. °° Studies of these composites are expected not only to provide a fundamental understanding of the conduction mechanism in the polymers, but also to lead to diverse electrical and optical properties. 

As intensive studies on the ECPs have been carried out for almost 30 years, a vast knowledge of the methods of preparation and the physico-chemical properties of these materials has accumulated [5-17]. The electrochemistry ofthe ECPs has been systematically and repeatedly reviewed, covering many different and important topics such as electrosynthesis, the elucidation of mechanisms and kinetics of the doping processes in ECPs, the establishment and utilization of structure-property relationships, as well as a great variety of their applications as novel electrochemical systems, and so forth [18-23]. In this chapter, a classification is proposed for electroactive polymers and ion-insertion inorganic hosts, emphasizing the unique feature of ECPs as mixed electronic-ionic conductors. The analysis of thermodynamic and kinetic properties of ECP electrodes presented here is based on a combined consideration of the potential-dependent differential capacitance of the electrode, chemical diffusion coefficients, and the partial conductivities of related electronic and ionic charge carriers. 

There is growing interest in biomimetic motions, which imitate the action of natural muscles. Since such motions are difficult to realize using conventional appliances such as mechanical, hydraulic, or pneumatic actuators, research efforts are focused on the development of new muscle-like actuators. Electroactive polymers (EAPs) including polymer gels [63], ionic polymer-metal composites (IMPCs) [64], conductive polymers [56], and carbon nanotubes [65] are candidates to address the performance demands. 

Redox active polymer films are ideally suited to tackling these issues. The properties of many of these electroactive polymers, e.g., their conductivity, charge distribution, shape, etc., can be changed in a controlled and reproducible way in response to environmental stimuli, e.g., a change in the nature of the contacting solution, an applied voltage, light intensity, or mechanical stress. 

The inertness of polymers could prove very beneficial if they possessed certain bulk properties such as electrical or magnetic susceptibility that one could exploit. We believe that the electroactive polymers, namely electronically and ionically conducting polymers, piezoelectrics, and electrets, by virtue of their susceptibility to either mechanical or electromagnetic or thermal or optical phenomena, could be utilized to interface between the external world and the physiological environment and could prove quite beneficial in eliciting the desired cellular response. These polymers represents a new modality in the development of interactive scaffolds for tissue stimulation, tissue regeneration, and the development of bioartificial organs. 

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