OPTICAL PARAMETERS OF POLYANILINE FILMS ON A POLYETHYLENE TEREPHTHALATE SUBSTRATE

Polyaniline (PAn) films, doped with citric acid, were synthesized on a polyethylene terephthalate substrate by chemical oxidative polymerization using ammonium peroxydisulfate as an oxidant. Optical band gap, Urbach energy, steepness parameter, absorption coefficient, extinction coefficient, the number of carbon atoms in a cluster, skin depth, refractive index were calculated. The change in the optical band gap for the synthesized samples was evaluated and it was found that the band gap decreases with increasing thickness of polyaniline films deposited on the polyethylene terephthalate substrate. It is established that the optical energies of the band gap of polyaniline films, estimated by the results of optical absorption measurements using Tauc methods, are in the range of 2.45–2.04 eV for film thicknesses equal to 76–270 nm, respectively. The Urbach energy values of the polyaniline coatings ranged from 0.57 to 2.24 eV with increasing polyaniline film thickness, respectively.The number of carbon atoms per conjugated length, the number of carbon atoms per cluster and refractive index for the present samples were determined. Based on the correlations between the optical energy of the band gap and the refractive index of semiconductors using Moss, Ravindra, Ravindra-Gupta, Reddy-Ahammed, Gerve-Vandamme, Kumar-Singh, Annani and Duffy-Reddy ratios, the value of the refractive index of polyaniline films was calculated. These values of the refractive index of polyaniline films were compared with the values obtained from the experimental results. From the obtained results it is seen that the refractive index of polyaniline films increases with increasing polyaniline film thickness on the polyethylene terephthalate substrate. The values obtained from the Ravindra is the closest to the experimental ones.