ABSTRACT
Inherently conducting polymers (ICPs) have attracted a huge number of research groups worldwide for nearly three decades [1-4]. The main ICPs are polyaniline (PANI), polyaromatics (e.g., polyparaphenylenes), and polyheterocyclic such as polypyrrole (PPy), polythiophene, and poly(ethylenedioxy)thiophene (PEDOT) of which chemical structures are shown in Fig. 1. ICPs can be synthesized electrochemically as thin films in the presence of a supporting electrolyte or chemically using FeCl3 and ammonium persulfate (NH4)2S2O8 as oxidants. The chemical route has the advantage of yielding much larger scales of products. Counteranions from the oxidant salts or added salts are instantly incorporated during the ICP synthesis because the oxidation potential for polymerization is higher than for doping the ICP-chain [5]. Therefore, chemically polymerized ICPs are always formed in the conducting state. However, they can also be switched reversibly to a neutral insulating form. In the conducting form, ICP chains bear positive charges that are counterbalanced by anions (e.g., Cl−, NO3−, SO42−), called dopants. The ratio of dopant-to-repeat unit is the doping level. The nature of the counteranion is one of the determining factors controlling the properties of the ICPs, like the level and stability of the conductivity [6, 7].
