Solvoconductivity of polyconjugated polymers: The roles of polymer oxidation degree and solvent electrical permittivity

Abstract

The solvoconductive properties of low-defect anodically coupled polypyrroles and polythiophenes, made so they are able to be solvated by organic vapors with suitable substituents, have been studied. The investigation was performed by contemporary conductivity and electrochemical quartz crystal microbalance analysis of the polymer films as a function of the solvent vapor partial pressure. Solvoconductivity was measured at two doping levels (lightly and heavily doped) of the polymers and for a series of solvents in a wide range of dielectric constants. Lightly doped polymers are responsive to vapors whereas heavily doped polymers do no respond at all. For the sensitive polymers the response follows the electrical permittivity of the solvent εs with respect to that of the polymer εp, in the sense that conductivity increases for εs > εp and decreases for εs < εp. A redox-type conduction model accounts for the responsive behavior of lightly doped polymers whereas a metal-like conduction model accounts for the absent responsivity of heavily doped polymers.