An experimental and theoretical investigation of the scaling laws governing the phenomenon of Maxwell-Wagner-Sillars interfacial polarization in composite materials in dependence on morphology, volume fraction, orientation of fillers, form factor and the presence of interphases is presented in the current study. By considering the complex dielectric function of the matrix and of the fillers, the dielectric spectra are calculated in the frequency range from 10(7) Hz to 10(-2) Hz and compared to dielectric measurements by Broadband Dielectric Spectroscopy, carried out in the frequency range from 10(7) Hz to 0.5Hz and between -90(o)C and 150(o)C. The characteristic frequencies of the global dielectric response are reported to strongly vary with the conductivity value of the conductive phase, while a much weaker dependence is observed upon varying the volume fraction, the form factor and the orientation of fillers. The value of permittivity at low frequency does not change with the conductivity value, whereas a significant variation is observed in dependence on the composite morphology, form factor, orientation of fillers and presence of interfaces with different gradients of properties. Two possible applications of our analysis are reported: (i) measuring the conductivity of materials without employing a direct electrical contact between the electrodes and the sample and (ii) discriminating different phenomena of electrical polarization in complex materials by analyzing the scaling laws. Our study delivers thus a useful and necessary analysis of the dielectric behavior of composite materials, where interfacial polarization effects play a major role.

An efficient approach to obtain polymeric materials with high permittivity values and low dielectric losses is presented in the current study. For this purpose, dielectric measurements by means of broadband dielectric spectroscopy, numerical simulations, and analytical calculations have been carried out for bilayer structures consisting in an insulating and a conductive polymer layer. Polyethyleneterephtalate and polytetrafluoroethylene have been used as insulating layers while, as conductive materials, blends of polyvinyl acetate with an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate. The dielectric properties of the samples have been investigated in a broad frequency (from 10(-1) to 10(7) Hz) and temperature range in order to determine, through the analysis of the scaling laws governing the interfacial polarization effects, the characteristic frequency ranges and the amplitude of the enhanced permittivity. An excellent agreement is found between the experimental results, the numerical simulations, and the analytical calculations. Finally, we show that bilayer polymeric materials with permittivity values as high as epsilon=556 and with low dielectric losses (tan()= 0.001) can be readily obtained by the current approach. This could have multiple applications, especially in the field of organic electronics. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47551.

Here we report a first analytical approach to determine the spectral dependence of the complex permittivity function of molecular and macromolecular ionic conductors in the interfacial layers formed by electrode polarization effects. We show that a previous model of electrode polarization effects that was successfully applied for describing the dielectric behavior of ionic liquids (Serghei, A.; Tress, M.; Sangoro, J. R.; Kremer, F. Electrode polarization and charge transport at solid interfaces. Phys. Rev. B 2009, 80, 184301) can be now generalized and applied for polymer/ionic liquid blends as well as for poly(ionic liquid)s. The determined dielectric function of the interfacial layers reveals a dramatic change in the charge transport process manifested by a large decrease in conductivity. Our approach brings the first evidence for a relaxation peak detected in the dielectric loss of the interfaces, which is attributed to an exchange process between the interface and the bulk. This study gives new insights into the mechanism of charge transport at interfaces and could thus contribute to a better correlation between the dielectric properties of ion conducting materials and their electrochemical behavior at interfaces.

The nutritional quality of new potatoes from intraspecific somatic hybrids called CN1 and CN2 was investigated and compared to that of the conventional Nicola and BF15 varieties. The chemical composition of tubers was determined to ascertain substantial equivalence. No significant difference in ash and mineral levels was noticed between all the potato samples. However, some differences were observed in dry matter, starch, soluble sugar, protein and lipid contents between hybrid potatoes and commercial varieties, but all values were within the normal ranges reported in the literature. The hybrid potatoes as well as the Nicola and BF15 varieties were then separately added to rat diet at a level of 30% (w/w). Animals were divided into five groups of 5 rats each. The rat group fed the standard diet served as control. The responses of rats fed diets containing hybrid potatoes were compared to those fed conventional potato varieties. Overall health, weight gain, food consumption and digestibility, aspects and relative weight of organs were comparable between rats fed with hybrid and with commercial potatoes. The results obtained show that the nutritional quality of the CN1 and CN2 potatoes is similar to that of commercial varieties.

The electrical and dielectric properties of ionic liquids measured by broadband dielectric spectroscopy are analyzed in detail, in order to determine the characteristic frequencies governing the spectral dependence of electrode polarization effects. A universal behavior is revealed: plotting the characteristic frequencies as a function of the DC-conductivity for a large variety of ionic liquids, single collapsing curves are obtained. This is due to the fact that the charge carriers present in ionic liquids have comparable molecular dimensions. Furthermore, an analytical approach is developed in order to determine, using the dielectric signature of electrode polarization effects, the dielectric properties of ionic liquids at metal interfaces. A new relaxation process taking place in the nanometric interphases formed at the contact with the measurement electrodes is reported. It is assigned to an exchange process between the interphase and the bulk.

The characteristic frequencies of electrode polarization and of interfacial polarization effects in dielectric spectra of ionic liquids and of polymer bi-layers are determined and systematically analyzed, based on dielectric measurements by means of broadband dielectric spectroscopy, numerical simulations, and analytical calculations. It is shown that, to a large extent, identical scaling laws can be derived for these two dielectric phenomena taking place at external and internal interfaces. Surprisingly, a fundamentally different behavior concerning the interrelation between the characteristic frequencies is found. This brings direct evidence that different manifestations of the phenomenon of electrical polarization can be discriminated by examining the inter-relation governing their characteristic frequencies, which can be of significant importance in disseminating the nature of different contributions appearing in the dielectric spectra of complex materials. Based on our analysis, we derive a new formula, valid for both electrode polarization and interfacial polarization effects, that allows one to determine the conductivity value from the frequency position of the Maxwell-Wagner-Sillars peak. An excellent agreement between experiment and calculations is obtained. The formula can be used, furthermore, to estimate the thickness of the interfacial layers formed due to electrode polarization effects. Values in the order of several nanometers, increasing with decreasing temperature, are reported.

The dielectric properties of composite materials consisting of a host matrix filled with spherical particles are investigated as a function of frequency by means of numerical calculations. Two different cases are analyzed: (a) composites with a conductive matrix and insulating fillers and (b) composites with an insulating matrix and conductive fillers. In both situations, dielectric dispersions due to interfacial polarization effects are observed in the dielectric spectra. In the present contribution, the characteristic frequencies of interfacial polarization effects are systematically analyzed in dependence on the volume fraction of the spherical fillers and on the conductivity values of the composite phases. The resulting scaling laws are discussed in detail.

Carbon nanotubes have been intensively studied because of their unique physical properties and many potential applications. One important application is when carbon nanotubes are used in polymer composites as novel conductive fillers to improve the dielectric properties of polymer blended with barium titanate (BaTiO3) ceramics. The three-phase composite with carbone nanotubes and BaTiO3 particles embedded into polyvinylidene fluoride (PVDF) were prepared by using a Haake blending mixer and pressed by hot-molding technique. The dielectric analysis show that the relative dielectric constant of the composite is slightly dependent on the frequency below 0.1 MHz and increases rapidly with MWCNT concentration. It is thus possible to reach a high dielectric constant equal to 7000. These films show interesting properties for an application in storage energy.