Characterization of Solution and Solid State Properties of Undoped and Doped Polyanilines Processed from Hexafluoro-2-propanol

Abstract

We have investigated the changes in the molecular conformation, morphology, and conductivity of polyaniline as it transforms from the insulating emeraldine base (PANI-EB) to the conducting emeraldine salt (PANI-ES) in solutions of hexafluoro-2-propanol (HFIP) and in films processed from the same solvent. Since both PANI-EB and PANI-ES dissolve in this single solvent, we are able to observe for the first time conformational changes as a function of the molar doping level, y. HFIP both solvates and complexes PANI-EB (i.e., y = 0) which promotes a disruption in secondary interactions between chains and allows individual polyaniline chains to adopt a more expanded molecular conformation. As PANI-EB is fully doped to PANI-ES (i.e., y = 0.50), a decrease in the GPC retention time and an increase in [η] argues in favor of an expanded chain conformation in HFIP. When the solvent is removed (under very mild conditions) from PANI-ES, the expanded molecular conformation is retained in the solid state, based on the strong absorption of the UV−vis/near-IR free carrier tail at 2500 nm and good room temperature conductivity. The results in this study indicate that the HFIP solvent can be used to process PANI-EB and PANI-ES with diversified dopant counteranions; in some cases, enhanced optical, conductivity, and morphology properties result from the use of this solvent.