Electrically induced contraction of zone-drawn polypyrrole films

The zone-drawing method was applied to electrochemically synthesized polypyrrole films at different heater temperatures under various applied tensions. It was found that the film could be zone-drawn by a factor of 1.4 at the drawing temperatures of 150–200 °C. The electrical conductivity and Youngʹs modulus increased to 327 S cm−1 and 3.6 GPa from 145 S cm−1 and 0.9 GPa of the as-synthesized film, respectively. When dc 3 V was applied in the drawing direction, the zone-drawn film exhibited contraction of 0.3% parallel to the electric field, while that perpendicular to the electric field reached 1.4%. The large anisotropy in contraction was explained by the orientation of polymer chains: the water vapor molecules sorbed on the conducting paths of polypyrrole chains aligned in the direction of the current flowing might desorb by the local Joule heating, thereby contracting the film in the lateral direction. The anisotropy, defined as the ratio of contractions between parallel and perpendicular to the electric field, was 4.6 under 3 V.