Electrochemistry and Expansion Behaviour in Polyaniline Film

The most electrically conductive state is the emeraldine salt (ES) that is between pernigraniline salt (Pas) at the high potential side and the leuco-emeraldine salt (LS) at the low potential side. The LS and the Pas are the most reduced and oxidised states, respectively, and have been found to be insulating. In an oxidation process from the LS to the ES, two electrons are withdrawn and two chloride ions are doped for every four benzene units. For the oxidation from the ES to the Pas, two electrons are withdrawn and two protons are released. The LS/ ES reaction is reversible, however, the hydrolysis occurs at the higher oxidised Pas states. 

The unstretched film and the stretched film perpendicular to the stretched direction show monotonous expansion during the oxidation LS ES Pas and vice versa [14]. The result possibly indicates that the dopant ions settle between the polymer chains. In the expansion of the film perpendicular to the stretched direction, irreversible expansion, namely, a creeping effect, was observed even under light load during the redox cycles [14]. 

---