Polypyrrole film synthesis via solution plasma polymerization of liquid pyrrole

Herein, a polymerization method is presented for forming polypyrrole films from liquid pyrrole using a solution plasma process (SPP) by adjusting the operating voltage waveform. Negatively or positively biased bipolar square-wave pulses were applied to a tungsten wire to generate plasma, while a copper tape served as a ground electrode as well as the metallic substrate for polymer film deposition. Solution plasma induced by negatively or positively biased bipolar square-wave pulses was mainly generated in the negative or positive half cycle of the operating voltage, respectively. Pyrrole anions, well known as strong bases, were generated by the SPP using the negatively biased bipolar square-wave pulse, which increased the pH level of the SP-processed pyrrole solution. The polypyrrole films were deposited onto the Cu tape, which served as the anode, only under this operation condition. Thereafter, the polypyrrole film, with a thickness of 22 µm and consisting of overlapped polypyrrole particles, was synthesized for 2 h. The differences in the discharge characteristics of the solution plasma driven by negatively and positively biased bipolar square-wave pulses initiated the formation of different reactive species of the pyrrole monomer. Based on these results, a mechanism for polypyrrole film formation using the SPP is proposed.