Conductivity ionically conducting polymers

This article addresses the synthesis, properties, and appHcations of redox dopable electronically conducting polymers and presents an overview of the field, drawing on specific examples to illustrate general concepts. There have been a number of excellent review articles (1—13). Metal particle-filled polymers, where electrical conductivity is the result of percolation of conducting filler particles in an insulating matrix (14) and ionically conducting polymers, where charge-transport is the result of the motion of ions and is thus a problem of mass transport (15), are not discussed. 

An example of an ionically conductive polymer is polyethylene oxide containing LiC104, which is used as a solid phase electrolyte in batteries. 

A completely separate family of conducting polymers is based on ionic conduction polymers of this kind (Section 11.3.1.2) are used to make solid electrolyte membranes for advanced batteries and some kinds of fuel cell. 

The first use of ionic liquids in free radical addition polymerization was as an extension to the doping of polymers with simple electrolytes for the preparation of ion-conducting polymers. Several groups have prepared polymers suitable for doping with ambient-temperature ionic liquids, with the aim of producing polymer electrolytes of high ionic conductance. Many of the prepared polymers are related to the ionic liquids employed for example, poly(l-butyl-4-vinylpyridinium bromide) and poly(l-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [38 1]. 

Noda and Watanabe [42] reported a simple synthetic procedure for the free radical polymerization of vinyl monomers to give conducting polymer electrolyte films. Direct polymerization in the ionic liquid gives transparent, mechanically strong and highly conductive polymer electrolyte films. This was the first time that ambient-temperature ionic liquids had been used as a medium for free radical polymerization of vinyl monomers. The ionic liquids [EMIM][BF4] and [BP][Bp4] (BP is N-butylpyridinium) were used with equimolar amounts of suitable monomers, and polymerization was initiated by prolonged heating (12 hours at 80 °C) with benzoyl... 

The active layer consists of a polymer having electronic conductive, ionic conductive, and luminescent properties, is blended with an ionic salt [48]. The polymer with the required properties can be realized by a blend of a conjugated and an ionic conductive polymer [481 or by specially designed polymers [71-73],... 

Figure 13. Schematic presentation of a small segment of polyheteromicrophase SEI (a) and its equivalent circuit (b) A, native oxide film B, LiF or LiCl C, non conducting polymer D, Li2CO, or LiCO, R GB, grain boundary. RA,/ B,RD, ionic resistance of microphase A, B, D. Rc >Rqb charge-transfer resistances at the grain boundary of A to B or A to D, respectively. CA, CB, CD SEI capacitance for each of the particles A to D.

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. 

The great capacity of conducting polymers to interact with electromagnetic or ionic radiation produces important applications, such as electromagnetic or ionic shielding. 

Figure 48. Evolution of the apparent diffusion coefficient (V as a function of solution ionic conductivity (x ) (Reprinted from H.-J. Grande, T. F. Otero, and 1. Cantero, Conformational relaxation in conducting polymers Effect of the polymer-solvent interactions. J. Non-Cryst. Sol. 235-237, 619, 1998. Figs. 1-3, Copyright 1998. Reproduced with kind permission of Elsevier Science-NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

Impedance spectroscopy is best suited for the measurement of electronic conductivities in the range 10 -7to 10 2S cm 1.145 In principle, it is perhaps the best method for this range, but it is often difficult to interpret impedance data for conducting polymer films. The charge-transfer resistance can make measurements of bulk film resistances inaccurate,145 and it is often difficult to distinguish between the film s ionic and electronic resistances.144 This is even more of a problem with chronoamperometry146 and chronopotentiometry,147 so that these methods are best avoided. 

Because of their high electronic conductivities, the rates of electrochemical processes in conducting polymers are generally controlled by ion transport. The ionic content of a film also has a strong influence on its... 

Figure 13. Schematic diagram of the measurement of the ionic conductivity of a conducting polymer membrane as a function of oxidation state (potential), (a) Pt electrodes (b) potentiostat (c) gold minigrid (d) polymer film (e) electrolyte solution (0 dc or ac resistance measurement.133 (Reprinted with permission from J. Am Chem Soc. 104, 6139-6140, 1982. Copyright 1982, American Chemical Society.)...

Figure 16. General transmission-line model for a conducting polymer-coated electrode. CF is the faradaic pseudo-capacitance of the polymer film, while Rt and Rt are its electronic and ionic resistance, respectively. R, is the uncompensated solution resistance.

Meanwhile, the R-R coupling (see Sect. 2.2) has evidently found general acceptance as the main reaction path for the electropolymerization of conducting polymers The ionic character of the coupling species explains why polar additives such as anions or solvents with high permittivity accelerate the rate of polymerization and function as catalysts. Thus, electropolymerization of pyrrole is catalyzed in CHjCN by bromide ions or in aqueous solution by 4,5-dihydro-1,3-benzenedisulfonic acid The electrocatalytic influence of water has been known since the work... 

For this reason, other types of electrolytes are used in addition to aqueous solutions (i.e., nonaqueous solutions of salts (Section 8.1), salt melts (Section 8.2), and a variety of solid electrolytes (Section 8.3). More recently, a new type of solid electrolyte is being employed more often (i.e., water-impregnated ionically conducting polymer films more about them in Chapter 26). 

In this chapter we focus on two electrochemically relevant, active polymer types ionically conductive polymers and electronically conductive polymers, and discuss new developments emerging in their context. 

In battery applications, new hthium ion batteries called lithium ion polymer batteries (or more simply but misleadingly, lithium polymer batteries) work with a full matrix of ionically conducting polymer, this polymer being present inside the porous electrodes and as a separator between the electrodes. They are offered in attractive flat shapes for mobile applications (mobile phones, notebooks). 

A special class of conductors are ionically and electronically conducting polymers (Sections 2.6.4 and 5.5.5). 

Another example of ion conducting polymer/ion/solvent systems are polyelectrolytes based on ion-exchange polymers, also called ionomers. The ionic conductivity of ion-exchange polymers is usually very low in the dry state, but increases abruptly by orders of magnitude upon addition of a... 

Mastragostino M., Arbizzani C., Soavi F. Conducting polymers as electrode materials in supercapacitors. Solid State Ionics 2002 148 493-8. 

Polymeric conducting systems were also prepared by in situ polymerization of vinyl monomers in ionic liquids [22], with a conductivity of 1 mS/cm. A conductive polymer electrolytes were also prepared by polymerization in liquid EMIm(HF)nF leading to a composite poly(2-hydroxyethyl methacrylate)-EMIm(HF)nF. Recently, polymer electrolytes were prepared in the form of thin foils, by incorporating ionic liquids in a polymer matrix [13-15], Conductivities of polymer-IL or polymer-IL-solvent systems are collected in Table 4. 

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