TRANSPORT AND STRUCTURAL-PROPERTIES OF POLYANILINE DOPED WITH MONOVALENT AND MULTIVALENT IONS

Sharp changes in the transport and structural properties were noticed when a pH-dependent study of polyaniline (PAN) with monovalent (Cl-) a nd multivalent (PO4)(3-) ions was carried out. Scanning electron micro graphs (SEM) of these samples reveal that the sharp changes induced by doping are more prominent at the pH where the transformation of the P AN lattice takes place. A channel formation has been observed at a pH of 3.0 in the case of HCl and 2.5 in the case of H3PO4 doping, with fl attening of the structure. The d.c. conductivity of the samples in thi s pH range has been measured in the temperature range 77-300K. The d.c . conductivity data have been analysed in the light of existing theore tical models. Mott's 3D variable range hopping (VRH) is the mechanism responsible for charge transport at low temperatures for HCl as well a s H3PO4 doped samples, whereas a deviation is observed at higher tempe ratures for all the HCl doped samples. However, lightly doped H3PO4 sa mples give a T-1/4 dependence. At a moderate doping level (pH 2.5), a deviation from 3D VRH is observed at higher temperatures, indicating t hereby a temperature and composition dependent charge transport. A les ser conductivity is obtained in the case of H3PO4 doping in comparison to HCl for the same pH value, which may be due to cross-linking induc ed by the multivalent ion. (C) 1997 Elsevier Science Ltd.