Effects of Pressure and Temperature on Conductivity of Highly Dedoped Polypyrrole

The effects of uniaxial pressure parallel to the current and the effect of temperature on resistance of highly dedoped polypyrrole samples were investigated. Polypyrrole samples were prepared electrochemically at 0.87 V constant potential from acetonitrile solution in presence of perchlorate anion as dopant on the gold sputtered glass as working electrode. Polypyrrole samples were dedoped chemically in NH3 for 1 h. Because of high resistance of polymer samples, the two-point probe technique could be applied for resistance measurements. Conductance of these highly dedoped polymers increases with pressure and temperature exponentially according to the Mottvariable range hopping theory (VRH). Change in the efficient number of states and also volume of the polymer due to the pressure can cause increases in the density of states near the Fermi level. Pressure should bring about an increase of orbital overlap, especially between the electron-rich of the neighbouring molecules. This increase of electron orbital overlap should be expected to increase the ease of inter-molecular electron transfer, by decreasing the distance and energy barriers to diffusion and tunnelling and by increasing the chain-chain areas of contact, thereby increasing the probability for electron transfer. So, the number of states that electron can hop from it would increase. With respect to the presence of numerous vacancies in highly dedoped polymer samples, a modified VRH model is introduced to fit the observed data based on the decreasing in polymer volume and increasing in the efficient number of states that electron can hop from it.