Structural and electrical characterization of polyanilines synthesized from chemical oxidative polymerization via doping/de-doping/re-doping processes

摘要

Structural characterization of various emeraldine salt (ES) and emeraldine base (EB) polyaniline (PANI) powders synthesized from chemical oxidative polymerization and then via de-doping and re-doping processes is first presented. Partial crystallinity with well-separated x-ray diffraction peaks is observed in the as-prepared ES PANI powder and an amorphous characteristic is identified in the de-doped EB PANI powder. From scanning electron microscopy, both the nanostructures of the as-prepared ES and de-doped EB PANI precipitated powders possess similar morphology. This finding reveals that the de-doping process to remove the counter-ions intercalated between the as-prepared ES PANI chains makes the de-doped EB PANI pieces become soft but does not change the nanostructures significantly. Then, the electrical conductivity perpendicular to the surface of the pressed PANI disc pellets is studied. The re-doped ES PANI pellets possess less electrical conductivity than their as-prepared counterparts, which suggests that during the re-doping process the counter-ions (Cl~- or HSO_4~-) are re-adsorbed predominantly on the surface region of the PANI nanostructures. Besides, the re-doping of larger HSO_4~- counter-ions (with respect to Cl~-) intercalated between the PANI chains increases the d-spacing of (100) planes and hence reduces the corresponding π-π inter-chain interaction. Finally, from the temperature dependence of the electrical conductivity together with the structural information, the charge carrier hopping mechanisms perpendicular to the surface of the pressed pellets corresponding to various PANI samples are compared and discussed.