**3.3.1 Doping anions**

Electrochemical polymerization of aniline, as mentioned before, is practically always carried out in strong acidic aqueous electrolytes. Doping anions incorporated in polyaniline originate from the acid, and represent its conjugated base. The dopant anions are inserted during electrochemical polymerization fulfilling the request of electroneutrality, and therefore their concentrations are on the stoichiometric levels, for its reasonable that their presence have strong influence on, polyanilne morphology, conductivity, and electrochemical activity and the polymerization process itself (Arsov et al., 1998; Cordova et al,. 1994; Dhaoui et al., 2008; Koziel, 1993, 1995; Lapkowski, 1990, 1993; Lippe & Holze, 1992; Okamoto & Kotaka, 1998; Pron et al., 1992; Pron & Rannou, 2002).

It was experimentally confirmed that polyanilne obtained in the presence of so called "large dopant anions", originated from hydrochloride acid, sulfuric acid, nitric acid, *p*toluensulfonic acid, and sulfosalicylic acid promoted formation of more swollen and open structured film, while the presence of "small ions" such is ClO4 - or BF4 -, resulted in formation of a more compact structure (Nunziante & Pistoria, 1989; Pruneanu et al., 1998; Zotti et al., 1988). The order of the polyaniline growth was also proved to increase with the size of the dopant anion (Inzelt et al., 2000). It was shown that addition of polyelectrolytes in polymerization electrolyte resulted in insertion of these molecules as dopants (Hyodo & Nozaki 1988, as cited in Wallace et al. 2009). It was also possible to obtain optically active polyaniline by electrochemical polymerization in the presence of (+) or (-) camphorsulfonic acid, leading to insertion of chiral dopants (Majidi et al., 2009).
