Characterisation of polyaniline conductive composites

We studied the optical, morphological, and transport properties of polyaniline (PANI) doped by camphorsulfonic acid in presence of cis-1,4-polybutadiene as film-forming agent. In particular, we have deposited PANI films by spin-coating at different speeds (800 rpm, 1000 rpm, and 1200 rpm) for 20 seconds on different substrates (glass, quartz, glass+ITO, glass+metallic pads). The morphology was studied by Atomic Force Microscopy (AFM) both in vertical and in lateral (shear-force) interaction mode. The comparison of the two different modes was performed in order to make apparent differences in the local stoichiometry of the film. The shear-force mode is able to measure the local friction parameter revealing eventual precipitate on the surface. For the vertical interaction mode we used a needle-sensor AFM by OMICRON to minimise the damage effect induced by the tip. From both measurements we obtained similar topographical images: it indicate a good homogeneity of the PANI film in terms of local chemical composition. To study the optical properties we used a CARY 5 spectrometer equipped with an integrating sphere (from LABSPHERE) that allows internal mounting of the sample to measure the transflectance. We were able to measure the diffuse and specular reflectance, the diffuse and specular transmittance, and the transflectance in the range 200-2500 nm. From the comparison of the different optical properties we determined the absorption bands and the refractive index. The electronic transitions were located at 1.4 eV and at 2.9 eV(valence band->polaronic band transitions), and at 3.6 eV (?->?* transition) in good agreements with the theoretical predictions. Furthermore we used a system of optical fibres (0.6 mm of diameter) attached to the CARY 5 spectrometer to test the local homogeneity of the optical properties. We measured also the values of sheet resistance of the films and of contact resistance. In particular we studied the transport properties versus temperature in order to determine the Fermi level position. We observed a linearity of the ohmic contact only for temperatures over 250 K, but at high bias the contact contribution to the total resistance was negligible for temperatures lower than 150 K.