NANO SIZE CONDUCTING POLYMER PREPARATION, PROPERTIES AND APPLICATIONS
Thin Film Laboratory, Department of Physics, Bharathiar University
Coimbatore - 641 046, Tamil Nadu, India (sunsakthi@yahoo.com)
Polyaniline-EB was synthesized chemically and doping was done using methylsulfonic acid. Polypyrrole was also prepared chemically Fourier Transform Infrared (FTIR) method was employed for the identification of the polymers.
XRD studies reveal that the casting Polyaniline-EB, (Pani-EB), Polypyrrole(PPY) / Polyaniline-EB films are amorphous in nature. Acid doped Polyaniline (Acid Pani) and PPY films are found to have crystalline structure. The studies on the dielectric properties have been carried out at different frequencies and temperatures with a view to study their effects on capacitance, dielectric constant and dielectric loss. Among the different polymer films studied, PPY / PAni-EB blend films possess stable capacitance values at all the frequency ranges studied and at temperatures upto 350 K. Also the dielectric loss values of PPY / Pani-EB blend films are very low and independent of frequency and temperatures up to 350 K throughout the frequency range studied. In addition, the PPY / Pani-EB blend films have constant dielectric permittivity values for a moderate frequency and temperature ranges. From these observations it can be concluded that PPY / Pani-EB blend films are the suitable candidate for thin film capacitors (having capacitance in the nano / pico farad range) at lower temperature ranges. All the polymer films of the present study possess a very low value of linear expansion coefficient (alpha).
The a.c electrical conduction study shows that the PPY and acid doped heavily doped Pani films are having high conductivity than the other films. It is found that a.c conductivity is proportional to n th power of frequency where n varies from 0.5 to 0.8 with the increase of temperature. DC conduction studies reveal that Poole-Frenkel type of conduction mechanism is predominant in Pani-EB and acid doped Pani films. The activation energy values of the films are evaluated.
Four probe studies indicate that polypyrrole (PPY) and acid pani films have high conductivity even at room temperature. For PPY film of thickness 0.1 micrometer, the conductivity is found to be 200 S/cm. Hall studies show that the carrier concentration of PPY is higher than that of all the other polymers studied in the present work. PPY and acid Pani have p-type of charge carriers while Pani-EB has both p and n-type of charge carriers.
The TEP studies indicate that the TEP values of the polymer films increase with the increase of both temperature and thickness. The low TEP values observed for PPY films certifythe metallic behaviour of these films.The thermally stimulated discharge current and pyroelectric studies of Pani-EB and acid doped Pani films reveal small peaks in the temperature range studied. The position of the peaks obtained vary only slightly with the polarizing field. The activation energies also show only a slight variation with the polarizing field. These factors support the dipolar orientation theory. The peaks observed at higher temperatures are more intense than the peaks at low temperatures.
Laser damage studies on these films show that Pani films are having higher threshold energy density than other olymer films. For acid Pani films of thicknesses ranging from 3 to 30 micrometer the threshold energy density varies from 120 to 220 m J cm-2 .