Residual water as a factor influencing the electrical properties of polyaniline. The role of hydrogen bonding of the polymer with solvent molecules in the formation of a conductive polymeric network

The influence of residual water retained in the emeraldine base form of polyaniline (PANI-EB) on its electrical properties (dielectric losses, a.c. electrical conductivity, complex electric modulus and impedance) is studied in the frequency range 10-105 Hz. It is found that the reduction of the ratio between water molecules and aniline units in the material from CH2O/CAn = 0.8 (when the polymer is maintained in an environment with 80% humidity) to 0.3 (the same polymer dried at 120 °C for 120 min) causes remarkable changes of the electrical properties of PANI-EB. The characteristic time of electrical relaxation increases by three orders of magnitude, with corresponding reduction of the electrical conductivity of the polymer. This means that each additional water molecule adsorbed at the structural unit of the polymer causes a one-order increase in its electrical conductivity. The effect is comparable with that caused by acid doping of PANI-EB and its partial conversion into the protonated form. The obtained data are interpreted in terms of a chemical model which assumes charging of polymer chains as a result of hydration of the double imine bond (C=N-) of PANI-EB. It is supposed that hydrogen bonding between polar molecules of solvents (water as well as some organic liquids) and aniline units of the polymer stimulates the formation of a highly conductive polymeric network.