Electrical conduction and dielectric relaxation in polyethylene terephthalate succinate

Abstract

SUMMARYElectrical conduction and complex permittivity are examined in polyethylene terephthalate succinate, focusing on their relations to dielectric relaxation processes. Both the real and imaginary parts of the complex permittivity, namely, the dielectric constant ε r g and the dielectric loss factor ε r gg , increase with a decrease in frequency, especially at high temperatures. They are both ascribed to the transport of ionic mobile carriers. Namely, the carrier transport forms a conduction current that should contribute to ε r gg . On this occasion, if charge exchange does not occur at the two electrodes, heterocharge layers should be formed before the electrodes. This should increase the charge density on the electrodes, thus contributing to ε r g . In addition to the increase in ε r g and ε r gg due to mobile ions, two relaxation processes, one due to micro-Brownian motion of dipoles and the other due to orientation and magnitude change of the dipole moment induced by two end groups in the polymer main chain, are observed. Corresponding to these two relaxation processes, two thermally stimulated discharge current (TSDC) peaks appear. The two TSDC peaks as well as the increments in ε r g and ε r gg become larger when the crystallinity of the sample decreases.

Dielectric properties of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate)

“…If we pay attention to the height of the plateau, it decreases with an increase in temperature. This appears to be strange if we compare this temperature dependence with the general behavior of r' that r' increases monotonically with an increase in temperature in most polymers [14][15][16][17][18][19][20][21][22][23]. As indicated by the red (light gray in b/w) and black arrows shown in Figure 6c, there are at least two shoulders in each spectrum, each of which shifts toward a higher frequency as the temperature increases.…”

“…In the two polymers, the slope of each straight line approaches -1 as the temperature increases. This indicates that electric conduction contributes significantly to r" at these high temperatures in the corresponding frequency ranges [14][15][16][17][18][19][20][21][22][23]. In this case, the relation between the electrical conductivity and r" should satisfy the following equation:…”