Synthesis of water soluble sulfonated polyaniline and determination of crystal structure

A polyaniline (PANI) was synthesized by the oxidative polymerization using ammonium persulfate as an oxidizing agent. The PANI was then stirred with excess fuming sulfuric acid at room temperature for 6 h to obtain water soluble sulfonated polyaniline (SPANI). The degree of sulfonation was found to be 93-94% from the Fourier transform infrared (FTIR) and elemental analysis. The solubility of the SPANI in water was 1.25 g/L at room temperature and appeared as a green color solution. Conductivity of the PANI was decreased after sulfonation. A proliferation of hydrophilic nature of the PANI after sulfonation was observed from the water contact angle measurement. From the UV analysis, it was revealed that the energies required for the π-π*and bipolaron/polaron transitions are less and the intensity of these transitions are lower in SPANI compared to those of PANI. A detailed study on the crystal structures of PANI and SPANI were accomplished from the powder X-ray diffraction analysis. The SPANI exhibited a more ordered structure having a higher degree of crystallinity and crystallite sizes with an increased unit cell volume compared to the PANI. After sulfonation the morphology of PANI was transformed from a rod-like shape to a flat-plate shape.