Impedance spectroscopy study of polyester/carbon nanotube composites

The electrical properties of carbon nanotubes loaded in polyester polymer matrix were studied by using the impedance spectroscopy technique. The study was carried out in the frequency range between 100 Hz and 1 MHz and temperature between 170 and 400 K. Cole-Cole representation was used to interpret the impedance spectra of all the samples. The variation of the electrical conductivity, as a function of temperature, for concentrations higher than the conduction threshold was analyzed. This variation undergoes a significant decrease from a critical temperature that corresponds to the phenomenon known as positive temperature coefficient in resistivity. Tunneling effect is responsible for the change of the conductivity. The carbon particles are not in physical contact and the electrons tunnel through the insulating polymer gap between particles. With the rise of temperature, the gap between particles increases and tunneling becomes less probable. Consequently, above this temperature, the electrical conductivity begins to increase, due to the fact that the temperature dependence of conductivity is mainly related with different thermal expansion of polymer matrix and carbon nanotubes. POLYM. COMPOS., 39:1297-1302, 2018. (c) 2016 Society of Plastics Engineers