Structural studies of halogen acid doped polyaniline and the role of water hydration

The structural ordering within crystalline polyaniline (PANI) powders as emeraldine (i.e., at 50% oxidation) in both its base (EB) and halogen acid doped salt (ES) forms has been studied using X-ray diffraction. PANI−ES powder precipitates, obtained immediately after synthesis, have significant crystalline fractions which nominally approximate the proposed pseudo-orthorhombic type I (ES-I) salt structure (Pouget, J. P.; et al. Macromolecules 1991, 24, 779). Additional treatments, such as dedoping by immersion in NH4OH solution and redoping by aqueous HF acid, lead to further changes in the structure with the appearance of additional crystalline phases. The role of water hydration in this structural evolution is also examined, and significant structural variations are found to occur with radically different time scales. Comparison of the data with structure factor calculations leads to new structural models that identify changes in the PANI chain packing and, in the case of HCl doping, correlate these with...