Synthesis of doped polypyrrole film by AC plasma polymerization

Abstract

This research designed and assembled an AC plasma system for the synthesis of polypyrrole films by AC plasma polymerization. Plasma polymerization parameters studied were voltage and reaction time in the range of 800-1500 V and 30-90 minutes, respectively. Polypyrrole films were characterized by various spectrophotometric methods. Infrared analyses showed absorption frequencies of important functional groups similar to observed in the case of chemically-synthesized materials. UV-Vis spectra of fabricated polypyrrole films suggested that the conjugative systems were decreased as increased the AC voltage and reaction time. Surface analysis by Scanning Electron Microscopy revealed a smooth surface at the voltage less than 1100 V. In addition, when the voltage is higher than 1100 V, there are grains appearing in it. Results from Energy-dispersive x-ray spectroscopy analysis were suggestive of the atomic ratio of carbon to nitrogen (C/N) of these films in the range of 4/1 to 5/1, comparing to the ideal C/N of polypyrrole at 4/1. The C/N ratio of plasma-polymerized polypyrrole films is somewhat higher than the ideal polypyrrole. This is in good agreement with a possibility of partial cleavage of a C-N and a C-C bond in the pyrrole rings during plasma polymerization. Electrical conductive measurements revealed that the undoped polypyrrole films exhibit higher conductivity (67.2 ×10-8 to 3.4×10-8 S/cm) than polypyrrole typically prepared from chemical and electrochemical methods. Compared to in situ doped polypyrrole films, the conductivities of polypyrrole films synthesized by ex situ doped were higher. However, it drastically decreased and reached undoped values in a short time (5 hours) whereas the conductivity of the one synthesized by in situ doped method could sustained for a long period of time (more than 120 hours).