Dielectric and optical properties of a poly(ethylene terephthalate) membrane in the temperature interval 150-400 K

Abstract

In this study, the dielectric and optical properties of poly(ethylene terephthalate) (PET) membranes were examined. The dielectric measurements were carried out in the temperature interval 150-400 K and in the frequency range 20 Hz-60 kHz. We analyzed in detail the temperature dependences of the dielectric permittivity and dielectric loss (tan δ) at various test frequencies. The relaxation tan δ peak, which appeared in the temperature range 150-300 K, was identified as the secondary β relaxation. The increase in tan δ at temperatures higher than 300 K could be explained as approaching the α relaxation. Optical measurements were performed in the UV-visible region from 200 to 400 nm at various temperatures between 150 and 400 K. The values of the direct and indirect band gaps were calculated at various temperatures. These values were lower for higher temperatures. An absorption peak was observed at a wavelength around of 285 nm at temperatures lower than 300 K. Such insight into the dielectric and optical responses of PET track membranes in a wide temperature range is particularly important when this material is used as a matrix for the semiconductor structure in the development of optoelectronic or microfluid devices.