Dopants anions/cations

If the dopant anion (A ) is small and mobile (eg. Cl ) and the polymer has a high surface area to volume ratio, then upon reduction the anion will be efficiently ejected from the polymer. However, extensive studies with polypyrroles have shown [4] that if the dopant is large and immobile (eg. if A" is a polyelectrolyte such as polystyrene sulfonate) then an electrically induced cation exchange process occurs, according to Eqn. 3,... 

FTIR spectroscopy has been used to monitor the conducting states of a conducting polymer as well as to know if a doping experiment is successful [86, 87], The FTIR and UV-Vis spectra of unsubstituted PANI is similar to that of substituted PANI though with slight band shifts. Doped PANI and its derivatives exist in the emeraldine salt forms which are essentially delocalized polysemiquinone radical cations whose stability is maintained by the presence of dopant anions. The degree of electron delocalization in the polysemiquinone forms of the doped PANI manifests itself in the form of an electronic-like band at ca. 1100 cm 1 associated with polarons [86], The structures of emeraldine base and emeraldine salt form of PANI are presented in Figure 6. 

Electrochemically prepared PPY films with a variety of dopant anions, such as chloride, bromide, sulphate and tosylate have been smdied by ToF-SIMS [360], No structural information on the cationic PPY chains, such as molecular fragment of pyrrole [M H]" at m/z = 66 and 68, was observed in the positive ion spectra. Similar conclusion has been reported for the PPY-fiber composites [361], Nevertheless, the molecular specificity of SIMS allows the distinction between the different dopant anions in the negative ion mode. The... 

In addition to nanostructural properties of the conducting polymer, considerable influence on actuation behavior has been demonstrated due to the choice of electrolyte. This has included properties of the solvent employed, and crucially the size of doping ions and their interaction with the conducting polymer. As mentioned above, PPy films doped with moderately small anions (e.g. CP) lead to actuation driven by anion movement. By contrast, it is generally found that the inclusion of a large dopant anion (e.g. DBS) within PPy leads to cation-driven actuation, typically when a smaller cation is employed (e.g. Na ). However, it is not always a simple matter of predicting which movement, anion or cation, will predominate for a particular electrolyte system, and for a particular type of... 

When a current or voltage is applied to the electrodes, the mcmomers are oxidized at the surface of the electrode. As a result of the initial oxidatitMi, the mraiomers form radical cations that react with other monomers in the electrolyte to form oligomeric products, as shown in Fig. 2. The extended jt-conjugation in the polymeric chain (i.e., polymerizatiOTi) is assisted by dopant anions, and the synthesis and doping of the... 

Equation (1) shows that the dopant anion leaves the polymer upon reduction. However, it was later proved that if the dopant anion is large and immobile (e.g., polystyrene sulfonate), then the cation from the supporting environment (electrolyte) is incorporated into the polymer [Eq. (2)]. Thus, the dopant anions have greater influence on the physico-chemical properties of the conductive polymer. 

In the case of polypyrrole, both of these situations have been reported. Obviously, then, the transport is optimized if it is dominated by only one diffusing species with a fast rate. In an attempt to ensure just this, a novel method was devised by the synthesis of a self-doped conducting polymer [60]. The key feature in this structure is the chemical anchoring of a dopant (anion) in the polymer chain itself, thus ensuring that cations are the mobile species during the redox process. Figure 4 shows the structure of the pyrrole-based polymer. 

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