DIELECTRIC-PROPERTIES OF THERMALLY AGED POLYANILINE FILMS DOPED WITH DILUTE SULFURIC-ACID

An experimental study of the frequency-dependent dielectric properties of thermally aged polyaniline (pAn) films as a function of the concen tration of the sulfuric acid solution used for dipping was performed. Inferring the morphological changes of the films from the results of u ltraviolet-visible (UV-vis) and infrared (IR) absorption spectra and d ifferential scanning calorimetry (DSC) thermograms, the dependency of the dielectric properties of thermally aged films on the protonation l evel is discussed. The effects of thermal aging on dielectric properti es may be subdivided into two temperature regions. In the temperature range lower than 170 degrees C, the dielectric constant was decreased, especially at high frequencies, and the tan delta-peak was shifted to lower frequencies with increasing aging temperature. The mobility of pAn chains and electric dipole appears to be gradually restricted with increasing temperature. In the range higher than 210 degrees C, pAn c annot be protonated and the dielectric properties are unaltered by dip ping in dilute sulfuric acid (pH = 2), owing to crosslinking and oxida tion of imine nitrogens.