Dopant counterion

The effect of this is that the charged defects are independent of one another and can form domain walls that separate two phases of opposite orientation and identical energy. These are called solitons and can sometimes be neutral. Solitons produced in polyacetylene are believed to be delocalised over about 12 CH units with the maximum charge density next to the dopant counterion. The bonds closer to the defect show less amount of bond alternation than the bonds away from the centre. 

PPS doped with AsFs dissolves readily in AsFs, but cast films are no longer soluble. Frommer has suggested that the solubilization mechanism involves solvation of both reactive radical intermediates and dopant counterions.f In addition, dialkyl esters of phosphoric acid dope PANi and render it soluble in certain solvents such as decalin. The resulting solutions can be mixed with conventional polymers and used to prepare films and fibers. 

The number of experimental variables available with chemical polymerization is greatly reduced because no electrochemical cell or electrodes are employed. The range of dopant counterions (A-) that may be incorporated into the PPy backbone during polymerization has also, until recently, been generally limited to ions associated with the oxidant. However, chemical polymerization remains of interest for processing purposes because it may be easier to scale up this batch process and it results in the formation of powders or colloidal dispersions. Furthermore, it is possible to use chemical deposition to coat other nonconducting materials. 

The use of halogens as oxidizing agents has also been reported,75 resulting in a PPy/X product containing halide (X-) ions as the dopant counterions. These same workers used chemical polymerization to produce PPy-polymethylpyrrole copolymers. 

Figure 10-2 7/t/e/chain charge mobility. Although the dopant counterion, ag., I (which also easts as I3" and Ij" ) has been omitted from these drawings, it may play a role in interchain transport. 

A very strong reducing agent and the presence of suitable dopant counterions are needed to introduce divalent cations into polyacetylene. Such a strong reducing solution can be made by dissolving the alkaline earth metals, calcium, strontium or barium in liquid ammonia (equation 1). 

The dopant level is the average amount of dopants (counterions) per unit monomer. 

SoKtons produced in polyacetylene are delocalized over approximately 12 CH units, with the maximum charge density to the dopant counterion. Soliton formation results in the creation of a new localized electronic state which is in the middle of the energy gap. At a high level of doping the charged sohtons produce soliton bands that can merge to behave hke a metalhc conductor. 

In any case, the thermal stability of electrochemically prepared polypyrrole can be improved by ion exchange of the dopant counterion [90,95]. The degree of stabilization achieved depends on the counterion (a greater effect is observed for sulfate and bisulfate anions), temperature, and duration of treatment. Although the mechanism for improved stability is not yet clear, it is apparent that the original polymer microstructure is important. 

A dopant counterion (A ) is incorporated during electrosynthesis to balance the charge on the polymer backbone. A wide range of dopants can be incorporated using this approach. Common chemical oxidants such as FeClg and (NH4)2S20s may also be used and these provide the anion from the oxidant, as the dopant anion A . In general, chemical oxidation provides ICPs as powders, while electrochemical synthesis leads to films. 

Self doped polymers are conducting polymers which carry a dopant counterion covalently bound to every monomer unit or to any number of monomer units. The principle of SDP is depicted in Scheme I, below ... 

This is substantially but not entirely correct for several reasons. Firstly, these bipolarons and other charge carriers are not truly mobile, coasting along from one end of an infinite polymer chain to another, as in the idealized 1-d conduction model. Rather, they are localized or confined by features such as defects or discontinuities in the extended conjugation (for example an sp defect in the idealized sp extended conjugation of P(Ac) or a cross link or ortho branch in the idealized head-to-tail chain of P(ANi)), and by attraction to dopant counterions which pin them down. 

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