Electroactive polymers polymeric electrolytes

Electroactive polymers 33 Electrolyte stability 45, 52 Electrophoretic mobility 54 Emulsion mobility 54 - polymerization 50, 53, 62 Environmental problems 45 Esters, activated I... 

Shi et al. have developed another method for the electrochemical polymerization of high oxidation potential monomers in boron fluoride ethyl ether (BFEE) which could yield highly conducting PT films (Scheme 9.4) [32]. As observed in the case of the electropolymerization of 3-methylthiophene, bithiophene 2T and terthiophene 3T, such improvement stems from the lower oxidation potentials at which the electropolymerization occurs in BFEE compared with those required in common electrolytes. Recent development of this strategy by the Reynolds group has shown that thiophene, 3-methylthiophene, 3-bromothiophene and 3,4-dibromothiophene can be polymerized in BFEE to yield homogeneous, electroactive polymer films, where their electrochemical polymerization in common electrochemical solvents has proved much more difficult [33],... 

Cyclic voltammetry can be used to estimate the charge transfer rate and also evaluate how this rate depends on parameters such as morphology and the chemical structure. The cyclic voltammetric examination of electroactive polymers is usually done in monomer-free solutions containing only the solvent and supporting electrolyte. In order to avoid the complication of mixed electrolytic equilibria, the supporting electrolyte and the solvent are usually the same as employed for the polymerization. Figure 3 shows the cyclic voltammogram (CV) of a polypyrrole film prepared in acetonitrile/tetra-w-butyl ammonium fluoborate medium. The anodic peak corresponds to polypyrrole oxidation, while the cathodic one corresponds to the reduction of this species. 

We do not discuss however the important field of polymer ionics and polymer electrolytes. This class of materials consists of polar macro-molecular solids in which one or more of a wide range of salts has been dissolved. A classic example that has been studied a great deal is the combination of poly(ethylene oxide) (PEO) containing LiX salt as solute. The reader is referred to a recent monograph edited by Scrosati and to review articles by Vincent, Linford, Owen and to a volume edited by MacCallum and Vincent for further information on this rapidly expanding area of polymer science. The major focus in this chapter (and indeed in this book) is on electroactive polymers used as electrode materials. Polymeric electrolytes, although important in both a technological and fundamental sense, present different problems to those discussed in this volume, and so we restrict discussion to electroactive polymer-based chemically modified electrodes. 

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 physical, chemical, and electrical properties of PPy can be easily modified by various doping agents and preparation conditions. There are many available dopant ions for the generation of good quality deposited polymer films [63-64]. Two of the most common dopants that are codeposited with PPy are polystyrene-sulfonate (PSS) and sodium dodecylbenzenesulfonate (NaDBS). PPy/PSS and PPy/NaDBS polymers have been used in many applications ranging from actuators and neural scaffolds to neural electrode coatings [22, 53, 61, 65]. It is reported that electrode materials, electrolyte solution, deposition methods (current-or potential-controlled deposition), deposition time, and solution temperature during electrochemical polymerization affect both the structure and electroactivity of PPy films [66]. 

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