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Noise and electrical transport properties of composites based on epoxy resin filled with various carbon inclusions (single-walled carbon nanotubes, high surface area carbon black, and exfoliated graphite) were investigated in depth. The temperature dependence of resistivity shows that Mott's hopping and tunneling between conductive carbon particles dominate the charge carrier transport at low temperature, whereas a positive temperature coefficient effect occurs at higher temperature. Low-frequency noise spectra of the investigated materials comprise 1/fα type components. The noise level is the highest for composites close to the percolation threshold. The percolation threshold value of the system also strongly impacts both the temperature dependence of the noise level and the resistivity. Close to the percolation threshold, the noise level increases due to the carrier tunneling throughout the polymer matrix and decreases due to the rapid expansion of the polymer matrix. In contrast, the latter has almost no influence on the noise level far above the percolation threshold, and the small kink in the temperature dependence of the noise level indicates a crossover between tunneling and thermally activated electron transport mechanisms. [ABSTRACT FROM AUTHOR]

This article deals with the dielectric properties of polydimethylsiloxane (PDMS) nanocomposites filled with SrTiO3 nanoparticles. The investigations were performed over a very broad range of frequencies (20 Hz to 3 THz). Almost no dielectric dispersion was observed in all the composites at room temperature over the entire range of measurement frequencies, and the dielectric losses were also very low under these conditions (<1.9). The dielectric dispersion was observed at lower temperatures (below 280 K), due to relaxation at the PDMS/SrTiO3 interface and in the bulk polymer. The relaxation time for both cases followed the Vogel–Vulcher law, while the freezing temperature was substantially lower for relaxation at the PDMS/SrTiO3 interface. [ABSTRACT FROM AUTHOR]

In this work, we report on the results of the examination of the nonlinear dielectric response of layered ferrielectic CuInP2S6 and Cu0.9Ag0.1InP2S6 crystals. The temperature behaviour of the nonlinear dielectric properties of ferrielectic CuInP2S6 and Cu0.9Ag0.1InP2S6 is found to be consistent with Landau theory. The additional peak of the third-order nonlinear susceptibility in these crystals, below the phase transition temperature, is strongly influenced by the electric field amplitude, and it is caused by the ferroelectric domain dynamics. The nonzero value of the second-order susceptibility and the mismatch between the temperatures of linear and third-order susceptibilities indicate that some polarisation exists above the phase transition temperature. [ABSTRACT FROM AUTHOR]

Properties of layered composites with carbon nanotube (CNT), GnP, Fe3O4 nanoinclusions, and hybrid composites with these nanoinclusions were investigated in the wide frequency range (from 20 Hz to 2 THz). All investigated composites (except with single Fe3O4 inclusions) are above percolation threshold. The strong enhancement of microwave and terahertz radiation absorption is observed in hybrid composites in comparison with composites with single inclusions. The synergy effect is discussed in terms of the complex impedance and the distribution of relaxation times. At low temperatures (below 200 K), the electrical conductivity of all hybrid composites follows the tunneling law model and the lowest potential barrier was estimated for composites with CNT inclusions. The best thermal properties are observed for composites with CNT inclusions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48814. [ABSTRACT FROM AUTHOR]

Broadband dielectric properties of epoxy composites containing the different additions of manganese ferrite (MnFe2O4) with two spherical particle sizes (28 and 60 nm) are studied in the wide temperature range from 150 to 500 K. The percolation thresholds in such systems are 30 and 29.3 vol% for small and large MnFe2O4 particles, respectively. The small difference in the percolation threshold value is related to a better distribution of larger nanoparticles. Composites above the percolation threshold are appropriate candidates for electromagnetic shielding applications. Above 380 K, the electrical conductivity is typical for all composites, both below and above the percolation thresholds due to the electrical transport in the polymer matrix. The activation energy strongly decreases with MnFe2O4 concentration indicating that the electrical transport occurs simultaneously in both MnFe2O4 and epoxy matrix subsystems. [ABSTRACT FROM AUTHOR]