A comparative voltabsorptometric study of polyaniline films prepared by different methods

A comparative cyclic voltabsorptometric study was carried out for polyanili ne (PAn) films prepared by electrochemical polymerization and vacuum therma l evaporation. The absorption values were measured at different characteris tic wavelengths (895, 755, 665, 435, and 325 nm) corresponding to the indiv idual absorption bands separated by us earlier from the spectra using the A lentsev-Fock method. Differential voltabsorptometric curves (dA/dt vs. pote ntial (DCVA)) measured in aqueous HCl were compared with ordinary cyclic vo ltammetry (CVA). The experiments for different sweep rates were also compar ed. It was found that the DCVA peak at 895 nm corresponds perfectly to the CVA peak both in the electrosynthesized and the vacuum deposited PAn. The D CVA peak at 435 nm (cation-radicals) precedes the CVA peak (similar to the maximum of the EPR signal), while that at 755 nm (polarons or cation-radica l dimers) lags behind the CVA peak. For the vacuum deposited films an inten se intermediate DCVA and current peaks (at about 0.6 V vs. Ag/AgCl) are obs erved. The results are discussed in terms of the heterogeneous structure of PAn; particularly, its specific features in the films prepared using diffe rent methods. (C) 2001 Elsevier Science Ltd. All rights reserved.