Polyaniline as viewed from a structural perspective

The local structural ordering of polyaniline (PANI) as emeraldine (i.e., at 50% oxidation) in both its base (EB) and salt (ES) forms has been studied using x-ray diffraction (XRD) techniques and these data reinforce the gener al belief that this local structure is extremely sensitive to the specific processing history. PANI powders precipitated as ES immediately following s ynthesis lead to reasonably crystalline materials whereas EB films cast fro m n-methyl pyrrolidine (NMP) solutions containing hydrogen bonding inhibito rs are fully amorphous. Dedoping, by further treatments of ES with NH4OH so lutions, or doping, by immersion of EB in aqueous HF solutions, lead to fur ther changes in the local molecular structure. Many of these structural pha ses bear a limited, resemblance to the previously proposed structures for H Cl-doped PANI powder and films [1,2]. The role of water hydration in the st ructural evolution is also examined and significant structural variations a re found to occur in ES at radically different time scales.