Effect of vacuum annealing on characteristics of the DBSA-doped polyaniline pellets

Powder of DBSA-doped polyaniline was pressed to pellets. The pellets were annealed in vacuum at 140, 200, 260 and 320 degrees C for times up to 120 min. For all the annealing temperatures, the conductivity of the pellet is sharply reduced by a factor of 2 when the annealing time reaches 15 min. For the annealing temperatures lower than 260 degrees C, the conductivity does not change with further increasing the annealing time. However, under the annealing condition of 260 degrees C/120 min, the conductivity of the pellet decreases markedly again. Furthermore, the pellets annealed at 320 degrees C for the times longer than 30 min exhibit an insulating characteristic. The pellets consist of many agglomerated particles. The agglomerated particles become large with thermal aging. When the annealing temperature reaches 320 degrees C, some small sub-particles are formed on the surface of the agglomerated particles. The annealing results in a de-doping of DBSA from the polymer backbones and promotes the formation of reduction state in the polyaniline. The DBSA-doped polyaniline pellets annealed have a more porous and cracked morphology relative to the pellet unannealed. The degradation of the conductivity of the DBSA-doped polyaniline pellets is attributed to the de-doping, the phase separation and the porous and cracked morphology. (c) 2007 Elsevier B.V. All rights reserved.