Polyaniline, sulfonic acid derivatives conductivity

The IBM group led by Brusic et al. [57,58] also studied the use of polyaniline derivatives for corrosion protection of copper as well as silver. The unsubstituted polyaniline, in neutral base form, provided good corrosion protection both at open-circuit potential and at high anodic potentials. The dissolution of metal (both Cu and Ag) was decreased by a factor of 100 when the metal surface was completely covered by the neutral polyaniline. However, polyaniline doped with dodecylbenzene-sulfonic acid (the conductive form of the polymer) increased the corrosion rate of Cu and Ag in water. The doped polymer in contact with the metal is spontaneously reduced at a rate faster than the oxygen reduction rate. The faster cathodic process in turn increases the overall rate of the anodic reaction, which is the dissolution of Cu and Ag, as opposed to the formation of a passive oxide layer. 

Polyaniline (PANI) can be formed by electrochemical oxidation of aniline in aqueous acid, or by polymerization of aniline using an aqueous solution of ammonium thiosulfate and hydrochloric acid. This polymer is finding increasing use as a "transparent electrode" in semiconducting devices. To improve processibiHty, a large number of substituted polyanilines have been prepared. The sulfonated form of PANI is water soluble, and can be prepared by treatment of PANI with fuming sulfuric acid (31). A variety of other soluble substituted AJ-alkylsulfonic acid self-doped derivatives have been synthesized that possess moderate conductivity and allow facile preparation of spincoated thin films (32). 

Aside from considerations of the polymer form itself, polyaniline can be doped and derivatized in a variety of ways. First, polyaniline can be polymerized in the presence of a variety of acids, which critically influences the resulting electronic properties [1-15]. The particular acid used and polymerization process employed can affect the degree of crystallinity observed [10-15,17-29]. Multiple dopants and substitutions have been achieved in the hope of increasing both the conductivity and solubility of these materials. The derivatives are simple polyanilines functionalized with complex ions such as aryl-SOj, camphorsulfonates, and perfluoroalkyl (and aryl) sulfonates. Dopants vary from simple anions, to oxyanions, to the more typical iodide ions [10-15,17-29,38-44]. The functionalization and/or doping affects, the band population, and the polyaniline chain conformation in turn influence the resulting electronic and structural properties of the polymer. 

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