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The chemically-synthesized emeraldine base form of polyaniline is soluble in aqueous acetic acid solutions, in which it presumably exists as the ‘doped’ emeraldine acetate salt. Films having a conductivity of ≈0.5 –2S/cm may be cast from the solutions. These films may be converted to relatively flexible, free-standing, lustrous, copper-colored films of emeraldine base, which can in turn be converted to free-standing, lustrous, dark blue films of emeraldine hydrochloride (θ≈1–2 S/cm). The resistance of films of both emeraldine base and 50% protonated emeraldine hydrochloride decreases by a factor of ∼2 when exposed to ∼4 Torr of water vapor. The resistance increases only very slowly on removing the water vapor under dynamic vacuum, consistent with the postulated structure of emeraldine hydrochloride involving ‘islands’ of heavily-doped emeraldine base in a matrix of undoped or slightly-doped material.
Angelopoulos et al. (Sat,) studied this question.