Conductive Electroactive Polymers oxidant

PAn is now accepted to have the general polymeric structure shown as 1. It differs from most other conducting electroactive polymers, such as polypyrroles (PPy s Chapters 2 and 3) and polythiophenes (Chapter 6), in that it possesses three readily accessible oxidation states. These range from the fully reduced (y = 1) leucoemeraldine state to the half-oxidized (y = 0.5) emeraldine form to the fully oxidized (y = 0) pernigraniline state. The ES form 2 is the state with the highest conductivity. 

Polythiophenes (PTh s) (1 shown subsequently) have much in common with polypyrroles. They are formed from a cyclepenta-diene molecule, but which has an S heteroatom. Thiophene is oxidized to form a conducting electroactive polymer (CEP), with the greatest conductivity obtained from a-a linkages. There are some important differences between polythiophenes and polypyrroles, and these are discussed here. 

Electropolymerizable monomers that give rise to conductive electroactive polymers (CEPs) provide a convenient approach for the immobilization of antibodies and other biomolecules for the creation of biosensors [5]. Polypyrrole has been explored for the immobilization of antibodies in immunosensors. Pyrrole monomer may be electrochemically oxidized (aqueous solution - -0.75 V vs. Ag/AgCl) to produce a highly conjugated and electron-... 

Conducting electroactive polymer (CEP). An electroactive polymer that, when oxidized or reduced, displays a significant change in intrinsic electrical conductivity. Examples Polyaniline, polythiophene. Also called electroconductive polymer (EP). 

In our own laboratories,we have used the fact the polymerization occurs in solution to develop a flow-through electrochemical cell to produce colloids i or water soluble conducting electroactive polymers (CEPs) continuously. The use of a highly porous anode (reticulated vitreous carbon — RVC) ensures that a high-surface area is available for electropolymerization and that a flowing solution can be used to prevent polymer deposition. The use of steric stabilizers (such as polyethylene oxide or polyvinylalcohol) in the flow-through electrolyte (see use of stabilizers under Chemical Polymerization) also helps prevent deposition and promote colloid formation. Both polypyrrole and polyaniline colloids have been prepared using this approach. 

The above mechanistic aspect of electron transport in electroactive polymer films has been an active and chemically rich research topic (13-18) in polymer coated electrodes. We have called (19) the process "redox conduction", since it is a non-ohmic form of electrical conductivity that is intrinsically different from that in metals or semiconductors. Some of the special characteristics of redox conductivity are non-linear current-voltage relations and a narrow band of conductivity centered around electrode potentials that yield the necessary mixture of oxidized and reduced states of the redox sites in the polymer (mixed valent form). Electron hopping in redox conductivity is obviously also peculiar to polymers whose sites comprise spatially localized electronic states. 

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. 

The oxidation and reduction (redox) processes in electroactive polymers (EAPs) make it possible to use these polymer materials as charge storage devices, either as battery electrodes or as supercapacitors. The potential for reduced cost, weight, and enviromnental impact of EAP electrodes relative to the metals and metal oxides that are traditionally used in such devices makes these polymers attractive alternatives. While inorganic options are limited, EAPs can be tailored to provide specific properties, such as conductivity, voltage window, storage capacity, porosity, reversibility, and chemical and environmental stability. 

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