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.