Polyaniline doping mechanism

Polyaniline provides the prototypical example of a chemically distinct doping mechanism [33,34], Protonation by acid-base chemistry leads to an internal redox reaction and the conversion from semiconductor (the emeraldine base) to metal (the emeraldine salt). The doping mechanism is shown schematically in Fig. II-2. The chemical structure of the semiconducting emeraldine base form of polyaniline is that of an alternating copolymer, denoted as [(1A)(2A)] , with... 

Figure 1. Schematic doping mechanism of emeraldine base polyaniline.

Aniline was the first example of the conjugated polymers doped by proton, it can be chemically oxidized by ammonium peroxydisulfate (APS). PANI has the advantages of easy synthesis, low-cost, proton doping mechanism, and is controlled by both oxidation and protonation state. Polyanilines are commonly prepared by the chemical or electrochemical oxidative potymerization of the respective monomers in acidic solution. But, other potymerization techniques have also been developed, including ... 

Chan et al. [188] first prepared the homopolymer of anthranilic acid and its copolymer with aniline by chemical polymerization in order to improve the solubility of polyaniline, to study the self-doping mechanism, and to evaluate thermal properties. The chemical polymerization of anthranilic acid was carried out using ammonium persulfate as the oxidant in the presence and absence of 1 M HCl. Copolymers of anthranilic acid and aniline were prepared in a similar manner by varying the monomer feed ratios in HCl at a pH of about 0.1. The... 

In contrast with the reaction with pyrrole, special precautions must be taken with polyaniline-coated textiles during the final washing and rinsing operation. The doping mechanism is somewhat different from the one in polypyrrole, and the counterion, e.g., chlorine orp-tolu-enesulfonic acid, can easily be partially removed by washing with water. It is therefore necessary to wash with water containing sufficient amounts of the counterion as demonstrated for polyaniline powders [63]. Because of the solubility and processibility of polyaniline... 

V. Luthra, R. Singh, S. K. Gupta, and A. Mansingh. Mechanism of dc conduction in polyaniline doped with sulphuric acid. Current Applied Physics 3, 219-222 (2008). 

In the context of this chapter, we focus on the undoped or lightly doped 7i-conjugated systems that are commonly referred to as organic semiconductors. Conducting polymers, such as PEDOT PSS, plexcore, polyaniline, polypyrrole, and others are not addressed here as their charge transfer mechanisms are rather different and would warrant an article in its own right. 

Properties of representative conducting polymers. Doped conjugated polymers have generated substantial interest in view of possible applications such as lightweight batteries, antistatic equipment, and microelectronics to speculative concepts such as molecular electronic devices.37-38 These polymers include doped polyacetylene, polyaniline, polypyrrole, and other polyheterocycles (Figure 5). While the conduction mechanism of metals and inorganic semiconductors is well understood and utilized in microelectronics, this is not true to the same... 

Polyaniline, polypyrrole, polyparaphenylene and polyacetylene (doped with SO , HSOj), added to the positive paste as powders or fibres, enhance the formation process and increase the capacity of the cells. The amount of polymers added to the paste should be within the range 0.8—2.0 wt%. Higher polymer loads impair the mechanical stability of PAM and hence the life of the battery is shortened dramatically. Polymers disintegrate on overcharge. Polyaniline has proved to be most stable on battery overcharge. 

Completely different monomers were called for. Before long, three of today s workhorses had been identified pyrrole, aniline and thiophene. In Japan, Yamamoto [38] and in Germany, Kossmehl [39] synthesized polythiophene doped with pentafluoroarsenate. At the same time, the possibilities of electrochemical polymerization were recognized. At the IBM Lab in San Jose, Diaz used oxidative electrochemical polymerization to prepare polypyrrole [40] and polyaniline. [41] Electrochemical synthesis forms the polymer in its doped state, with the counter-ion (usually an anion) incorporated from the electrolyte. This mechanism permits the selection of a wider range of anions, including those which are not amenable to vapor-phase processes, such as perchlorate and tetra-fluoroborate. Electrochemical doping also overcomes an issue associated with dopants... 

By the mid-80s it was clear to most researchers that success on the conductivity side had taken its toll on polymer processability. Attention turned back to restoring the solubility and mechanical properties of the polymer. Polyaniline received the most attention initially. The nonconductive emeraldine base form is soluble in A-methylpyrrolidone [28] and films can be cast. Subsequent doping with a protonic acid from aqueous solution, or in situ with a photo-acid generator [45], is necessary to achieve conductivity. Polyaniline is also soluble in sulfuric acid, not the most convenient of solvents. Nevertheless it proved possible to spin fibers [46], cast films and extmde sheets of conductive polyaniline sulfate, but the laboratory experiments did not make the transition into large-scale manufacmring. 

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