OBSERVATIONS OF POLYANILINE SURFACE-MORPHOLOGY MODIFICATION DURING DOPING AND DE-DOPING USING ATOMIC-FORCE MICROSCOPY

Chemically synthesized 30 mum thick polyaniline films were studied dur ing the doping and de-doping process by imaging the polymer surface us ing in situ atomic force microscopy (AFM). The polymer, which was init ially in the base non-conducting form, was doped using aqueous solutio ns of both tosylic acid (pH = 0.2) and HCI (pH = 0.2 and 1.0). De-dopi ng was accomplished by exposing the same doped polymer surface to NH4O H (pH = 12) base solution. AFM images showed that it was necessary to cycle the polymer surface three times between acid and base before a r eproducible 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 approximately 5.4 and approximately 6.7 nm, resp ectively. In addition there appeared to be an increase in the size of surface channels and cracks. When doping with HCI (pH = 1.0), no chang e in surface morphology was observed; however, noticeable surface roug hening occurred over 10 min for the case of the lower pH = 0.2 solutio n; mean roughness changes for the base and acid conditions were approx imately 1 7.9 and 39.2 nm. Radio frequency measurements, which determi ned the polymer complex permittivity, and d.c. conductivity measuremen ts were used to determine the level of doping in the samples studied b y AFM which were exposed to acid solutions.