Observations of polyaniline surface morphology modification during doping and de-doping using atomic force microscopy

Chemically synthesized 30 m thick polyaniline films were studied during the doping and dedoping process by imaging the polymer surface using in situ atomic force microscopy (AFM). The polymer, which was initially in the base non-conducting form, was doped using aqueous solutions of both tosylic acid (pH = 0.2) and HCl (pH = 0.2 and 1.0). De-doping was accomplished by exposing the same doped polymer surface to NH₄OH (pH = 12) base solution. AFM images showed that it was necessary to cycle the polymer surface three times between acid and base before a reproducible surface morphology was established. For the case of doping with tosylic acid, AFM images showed that the polyaniline surface was immediately roughened; the changes in mean roughness for the base and acid conditions were ~ 5.4 and ~ 6.7 nm, respectively. In addition there appeared to be an increase in the size of surface channels and cracks. When doping with HCl (pH = 1.0), no change in surface morphology was observed; however, noticeable surface roughening occurred over 10 min for the case of the lower pH = 0.2 solution; mean roughness changes for the base and acid conditions were ~ 17.9 and 39.2 nm. Radio frequency measurements, which determined the polymer complex permittivity, and d.c. conductivity measurements were used to determine the level of doping in the samples studied by AFM which were exposed to acid solutions.