Manipulating structure and enhancing conductivity of polymer acid doped polyaniline by exploiting redox chemistry

• The oxidation state of films comprising polymer acid-doped polyaniline is cycled.
• While in its reduced oxidation state the structure of the film is allowed to relax.
• Following relaxation, the film is oxidized back to its conductive oxidation state.
• The electrical conductivity of the film increases dramatically after redox cycling.

By reversibly accessing the oxidation states of polyaniline that is template synthesized on poly(2-acrylamido-2-methyl-1-propanesulfonic acid), extensive structural relaxations are induced that result in significant conductivity enhancement. The electrostatic interactions between polyaniline and its template can be neutralized through chemical reduction with hydrazine monohydrate, after which the polymer acid can be plasticized by water vapor to drive structural relaxation. Exposure to nitric oxide leads to re-oxidation of polyaniline and concurrent reassociation with its polymer acid dopant. Following this redox cycling process, the conductivity of polyaniline films increases from 0.4 S/cm to as high as 11 S/cm. This enhancement is attributed to the same extensive polymer chain relaxation and the simultaneous elimination of the particulate nature of template-synthesized polyaniline previously described following solvent annealing in dichloroacetic acid. While solvent annealing also increases the conductivity of films comprising commercially available poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid), redox cycling induces no improvement in the electrical conductivity of such films. This difference suggests that conductivity enhancement in poly(3,4-ethylenedioxythiophene) films through solvent annealing stems from a mechanism markedly different from the structural relaxation responsible for improving the electrical properties of polymer acid-doped polyaniline, and likely results from the physical removal of an insulating poly(styrene sulfonic acid) overlayer.