DIPOLE AND HYDROGEN-BONDING INTERACTIONS IN POLYANILINE - A MECHANISM FOR CONDUCTIVITY ENHANCEMENT

Experimental and theoretical evidence indicate that polyaniline and its oligomers interact strongly with polar and/or hydrogen-bonding molecules. Empirical studies of the solubility properties of doped and undoped polyaniline indicate strong components to the cohesive energy density arising from polar and hydrogen-bonding interactions. Calculations on model oligomer compounds by semi-empirical and force field methods indicate that such interactions with inserted solvent molecules cause a redistribution of charge on the backbone in the direction of the equilibrium distribution characteristic of the bare radical cation (polaron) in the absence of a counterion. By lessening the polarization effects of the counterion, polar and/or hydrogen-bonding solvents, such as water or m-cresol, can contribute to a reduced scattering cross section for defects created by the polarization effects of the dopant anion. Such an effect can account for the reversible enhancement of the conductivity of polyaniline that is brought about by complexation with polar molecules such as water.