Protonation and deprotonation of polyaniline films and powders: effects of acid and base concentrations on the surface intrinsic oxidation states

The effects of acid and base concentrations used during the protonation-deprotonation cycle on the surface intrinsic oxidation states ([=N-]/[-NH-] ratios) of emeraldine (EM) base films and powders were evaluated quantitatively by X-ray photoelectron spectroscopy (XPS). The [=N-]/[-NH-] ratios of the EM base films were enhanced to substantially above unity or were reduced to substantially below unity, depending on whether the base (NaOH) concentrations used during the protonation-deprotonation cycle were above or below 0.1 M, respectively. On the other hand, although the intrinsic oxidation states of EM films decrease with decreasing acid (H2SO4) concentration used during the protonation-deprotonation cycle, the [ =N-] /[-NH-] ratios remained well above unity after the cycle. The intrinsic oxidation states of the EM base powders were not significantly affected by the changes in acid or base concentration during the protonation-deprotonation cycle. The observed phenomena were explained in terms of the diffusion limitations and different extents of hydrolysis reaction associated with the sample morphologies and changing acid or base concentration. (C) 1998 Elsevier Science S.A.