Secondary doping in polyaniline

Phenomenologically, a primary dopant for a conducting polymer is a substance, a relatively small quantity of which drastically changes the electronic, optical, magnetic, and/or structural properties of the polymer and it is accompanied by a large increase in conductivity. De-doping results in a reversal of the newly-induced properties. Phenomenologically, a secondary dopant is an apparently “inert” substance which, when applied to a primary-doped polymer, induces still further changes in the above properties including a further increase in conductivity. It differs from a primary dopant, in that the newly-enhanced properties may persist even upon complete removal of the secondary dopant. The concept will be illustrated using polyaniline and its derivatives. It will be shown that the effects of secondary doping are based primarily on a change in molecualar conformation of the polyaniline from “compact coil” to “expanded coil” during the secondary doping process.