Impedance analysis of single walled carbon nanotube/vinylester polymer composites

This study presents impedance characteristics of single walled carbon nanotube/vinylester (SWCNT/VE) glass fiber reinforced polymer (GFRP) composites. The impedance measurements were carried out as a function of the frequency over range of 10(-2) and 10(7) Hz at various temperatures between 300 K and 420 K. Bode and Nyquist plots of real and imaginary parts of complex impedance (Z*) were obtained and Cole-Cole approach was used to interpret the impedance characteristics. The results indicated that the bulk resistance of the material decreases significantly as the temperature increases. The frequency-dependent AC conductivities were calculated using the complex impedance data and dimensions of specimen. It has been observed that the alternating current values are compatible with the Jonscher's power law. The behavior of dielectric constant and loss factor at the various temperatures were analyzed as a function of applied frequency. While the sample exhibited high dielectric permittivity in the low frequency region with the Maxwell-Wagner-Sillars (MWS) effect, it was observed that the permittivity decreased as a result of the dipoles' inability to rotate themselves in the field direction at high frequencies. No dielectric relaxation peak was observed in the loss spectra in our limits. From the results, it can be said that the contribution to the dielectric relaxation is due to the interface polarization and DC conductivity. Electric modulus formalism was also used to describe the conductivity and dielectric relaxation processes of SWCNT/VE binary composite. It was found that the obtained peak maximums shifted to higher frequencies as the temperature increased. It is concluded that the frequency regime below the peak maximum defines the range of mobile charge carriers, and in the regime above the maximum, the charge carriers are limited to short distance potential wells.