Nobutaka Nakamura

Measurement of dielectric properties of polymers using Fourier analysis

Abstract A dielectric spectrometer has been developed which employs Fourier analysis methods for an accurate, straightforward determination of the complex dielectric constants of solid and liquid polymeric materials in the frequency range 10–105 Hz between 120 and 770 K. On application of an electric field to the sample, the response of the sample is the electric displacement which is collected by the current detector circuit. The amplitude and phase relation between the applied electric field and the collected current is analysed using a Fourier transformation circuit and output as the complex dielectric constant. The structure and performance of the apparatus are described in detail. An example of a dielectric measurement using Nylon 6 films, where the effect of moisture on the dielectric relaxations has been studied, is presented. The activation energy of the observed α-relaxation has been calculated using commercial software.

The influence of moisture on the dielectric properties of poly(ethylene-co-vinyl alcohol)

Abstract The influence of moisture on the dielectric properties of poly(ethylene-co-vinyl alcohol) copolymer (EVA) has been investigated using a Seiko DES 100 dielectric spectrometer between 170 and 385 K in the frequency range 10–100 kHz. A scanning rate of 1 K min−1 was used. Two peaks were observed. The α-relaxation is ascribed to the glass transition. The presence of water facilitates molecular motion, shifting the α-relaxation to lower temperatures. The β-relaxation is due to the local-mode relaxation in the crystalline regions of the copolymer or to the motion of hydroxyl groups. At low temperatures, water molecules may form mechanically stable bridges between the vinyl alcohol regions of the copolymer chains which inhibit molecular motion.