Anions dopant counterion

Coating by a thin layer of PPy has been realized on multiwalled nanotubes (MWNT) [29,91,93], well-aligned MWNT [85] and single-wall nanotubes (SWNT) [88], When MWNT are oxidized, their surface is covered with oxygenated functionalities, which can be used as anionic dopant of a PPy film electrodeposited on the MWNT [94], These films are notably less brittle and more adhesive to the electrode than those formed using an aqueous electrolyte as source of counterion. 

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. 

A counterion (A ) is incorporated during synthesis to balance the charge on the polymer backbone. Common chemical oxidants are FeClj and (NH4)2S20g, which provide Cl and HS04 /S04, respectively, as the dopant anions. Electrochemical oxidation provides greater flexibility in terms of the anion that can be incorporated from the electrolyte (MA salt or HA acid) added to the polymerisation medium. 

In an effort to produce polymer films with improved mechanical properties in aqueous solutions, pyrrole was electrochemically polymerized in the presence of surfactants such as sodium dodecylsulfate and sodium dodecylbenzenesulfonate. In the case of dodecylsulfate anion, the polymers switched between a transmissive yellow in the neutral state to violet when partially oxidized and brown when fully oxidized [97]. When electropolymerized in the presence of dodecylbenzenesulfonate anion, the polymer films switched between a transmissive yellow when neutral to dark blue when oxidized [98]. In both cases, the polymers showed an improved electrochemical stability over polymer films produced with other inorganic counterions. This has been attributed to the binding of the surfactant dopant within the film during charge compensation since there is less mechanical distortion of the polymer film. 

---