Dielectric relaxation spectroscopy of polyethylene terephthalate (PET) films

Abstract

The dielectric properties of biaxially stretched polyethylene terephthalate (PET) films of thickness and 68% degree of crystallinity were investigated by means of dielectric relaxation spectroscopy in the frequency range Hz and the temperature range C. Differencial scanning calorimetry (DSC), in the range C, was employed to investigate the thermal properties of the PET samples. Besides measuring the relaxation associated with the glass transition and the secondary relaxation, special attention has been paid to the investigation of DC-conductivity-related effects. They give rise to high dielectric permittivity values and dielectric losses at low frequencies and high temperatures. The results are analysed within the complex permittivity formalism and discussed in terms of interfacial Maxwell - Wagner - Sillars polarization, the peak, conductivity relaxation, space-charge polarization, electrode polarization and DC conductivity. DC conductivity values determined from frequency plots of the AC conductivity follow the Vogel - Tamman - Fulcher equation at temperatures higher than the glass transition temperature, indicating that the charge-carrier transport mechanism is governed by the motion of the polymeric chains. On the basis of the temperature dependence of the DC conductivity PET is classified as a fragile system.

Electric measurements with constant current: A practical method for characterizing dielectric films

“…From the plot of Fig. 7, reasonable values for the dielectric constant were obtained, 21 confirming that the Poole-Frenkel conduction model is appropriate to explain the experimental results with the CC method. This is not surprising since it is well known that the Poole-Frenkel conduction plays an important role in PET polymer.…”

“…14 Finally, it was shown that the electric conduction in PET obeys the Poole-Frenkel law in agreement with published data. 21,22 Theoretical models for CC measurements are already available and described in the literature 12 for several cases such as free charge injection and charge injection in the presence of trapping. Such models were originally applied to corona charging measurements under open circuit but they are the same for closed circuit measurements.…”

Dielectric relaxation spectroscopy of reactively blended amorphous poly(ethylene terephthalate)–poly(ethylene naphthalate) films

“…These blends are initially immiscible but quickly react and phase structure changes via transesterification in the melt. Whilst the dielectric properties of PET [5,6] have been investigated, PEN has been much less investigated [7]. Ezquerra et al [8] undertook a detailed study into the primary and secondary relaxations of amorphous random copolymer films of PET and PEN.…”

The thickness dependence of dielectric properties in the plasma polymer thin films

“…Thermal, electrical and mechanical properties of polymers are useful for use in technological and biological applications [1][2][3][4][5][6][7]. Thin polymer films obtained by plasma polymerization are generally more biocompatible than conventional biomaterials such as Silastic.…”

“…[12,13,21,22]. In addition, there are reports on the dielectric properties of [2,23,24] and on the comparison of their dielectric properties with the structural properties of plasma polymers [25][26][27][28][29]. However, there are no reports on of the pPEO dependent on the film thicknesses.…”