Investigation Of Polymerization Of Pyrrole By Atmospheric Dielectric Barrier Discharge

In this article, polypyrrole (PPy) films were synthesized by atmospheric pressure dielectric barrier discharge. The effects of electrode materials, electrode geometry and discharge power on the morphology, crystallinity and chemical structure of PPy films were investigated. The voltage-current relation of the discharge and the emission spectra were discussed.Deposited in the plasma reactor of bare ferronickel electrodes for 1-3 minutes, the glass slide was found to have nanowires of 500nm in diameter, 3 mm in length at most on its surface, proved to be single crystallines according to their lattice fringes by HRTEM (high resolution transmit electron microscope) and sharp diffraction spots by SAD (selected area diffraction). The discharge power was important to the crystallinity of PPy: large power tended to produce long single crystalline nanowires, whereas small one amorphous nanopowders. The FTIR (Fourier Transform InfraredSpectroscopy) of deposited film from pyrrole is similar to that of pyrrole, which means that PPy film maintained the basic structure of pyrrole. But the intense absorption near 1384cm~-1 of PPy film, corresponding to the stretching vibration of C=C, indicated a large conjugated π -electron structure. In the current-voltage curve, the overall current can be treated as the sum of displacement current and micro-discharge current. The phase of displacement current was π /2 smaller than that of voltage. The micro-discharge began at zero-point of voltage in every cycle.The results of SEM, TEM and SAD displayed that PPys synthesized in the reactor with fully covered electrodes were mono-dispersed, amorphous and elliptic or rod-like shaped particles, whose long and short axes were 1 μm and 0.1μm respectively. Laser diffraction methods also proved that these particles were mono-dispersed in water. Excited by 380nm laser, PPy water solution exhibited fluorescence between 460~480nm, which was first discovered without doping. Discharge power could alter the intensity and position of emission peaks as well as those of the corresponding Ultraviolet-visible Absorption Spectrum (Uv-Vis). This was caused by the different conjugated extent of PPy changed by the discharge power. The FTIR of amorphous PPy particles resemble that of single crystalline PPy, suggesting that their chemical structures were similar.According to the above data and results, it is concluded that atmospheric pressure dielectric barrier discharge is a new, fast and environmental method of synthesizing conjugated polymer. Through controlling electrode characteristics, such as discharge power and flow rate of monomer, single-crystalline PPy could be obtained. With its distinctive character compared with traditional ones, plasma polymerization at atmospheric pressure can have wide applications in industry.