Characterization of solution and solid state properties of undoped and doped polyanilines processed from hexafluoro-2-propanol

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, gamma. HFIP both solvates and complexes PANI-EB (i.e., gamma=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., gamma=0.50), a decrease in the GPC retention time and an increase in fill 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.