Spectroelectrochemical study of vacuum deposited polyaniline films subjected to postdeposition treatment by HNO3

Thin polyaniline (PAN) films were prepared by evaporation of emeraldine bas e in vacuum at 275-325 degrees C, followed by deposition of the vapors onto SnO2-glass transparent electrodes. With the purpose to restore the origina l structure of the polymer, the films were subjected to a postdeposition ox idative treatment in HNO3 according to the following three different proced ures: (1) treatment in vapors of 10 M acid, (2) treatment in 2 M HNO3 aqueo us solution, (3) cyclic treatment: in 2 M aqueous HNO3, then in 2 M aqueous NH, and so on. Electrochemical and spectroelectrochemical characteristics, namely cyclic voltammetry curves at different sweep rates and optical spec tra at stationary potentials, were investigated for these films. It was fou nd that the above characteristics of the films oxidized according to the cy clic procedure are most close to those of conventional PAN. However, in the optical spectra recorded at 0.0 V (vs. Ag/AgCl) for all the vacuum deposit ed films no absorption band in the area longer than 800 nm was observed. Th e results are discussed in terms of correlation of changes in the spectroel ectrochemical characteristics with formation of heterogeneous structure of PAN by means of arising of intermolecular interactions, as well as, with sp ecific features of vacuum the deposited PAN films. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.