Browsing by Author "Kovalchuk, T. M."
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- Effect of biochar binding on dielectric properties of color catcher sheetsPublication . Kovalchuk, O. V.; Prochazkova, J.; Kovalchuk, T. M.; Volokh, L. V.; Oleinikova, I. V.; Mariano, José; Safarik, I.; Kopansk, P.The dielectric properties in the frequency range of 102 to 106 Hz and at the temperatures of 30 to 60 °C of 0.4 mm thick color catcher sheets (nonwoven textile with ion exchange properties) both in the native state and with bound biochar were investigated using the oscilloscope method. The sample dimensions were 1×1 cm. To assess the influence of the sample thickness, samples with several (maximum 4) layers were used together with one-layer textile. It was shown that, unlike the data obtained by us earlier, the dielectric properties of the nonwoven textile without additives are caused by near-electrode processes. It was demonstrated as well that in this case, the dispersion of the frequency dependences of inverse resistance (analog of the imaginary component of complex dielectric permittivity) with respect to capacitance (analog of the real component of complex dielectric permittivity) corresponds to the Debye dispersion. Using the obtained results, the dielectric relaxation time (2.4·10–5 s) and the thickness of the near-electrode layer (1.5 μm) were estimated. Measurements at different temperatures and with several layers of the native textile demonstrated that the parameters of this relaxation process do not depend on both the sample thickness and the temperature. It was found that the sample resistance decreased by 3 orders of magnitude on average in the presence of biochar bound to the textile. In this case, the temperature dependence of the inverse resistance (analog of conductivity for uniform and continuous bodies) obeyed the Arrhenius law. The activation energy of the temperature dependence of the inverse resistance was 0.37 eV, which is greater than the similar value obtained in our work of 2024.
- Effect of modification of nonwoven textiles with biochar and multi-walled carbon nanotubes on their dielectric propertiesPublication . Kovalchuk, O. V.; Prochazkova, J.; Kolanowska, A.; Mariano, José; Boncel, S.; Zolochevska, K.; Kovalchuk, T. M.; Kopčanský, P.; Safarik, I.Dielectric properties of native nonwoven textile as well as textile with bound biochar and multi-walled carbon nanotubes in the frequency range of 10 to 5·105 Hz and at the temperatures of 30 to 60 °C have been investigated. The capacity of native nonwoven textile has been shown to decrease with the temperature according to the Arrhenius law. The activation energy of the temperature dependence of the capacity has been estimated to be 0.09 eV. It has been demonstrated that regardless of the temperature, the frequency dependence of the resistance of the nonwoven textile can be described by two exponential functions. In the presence of bound biochar and multi-walled carbon nanotubes in the nonwoven textile, the conductivity current was 4 orders of magnitude greater than the bias current and increased with the temperature according to the Arrhenius law. The activation energy of the temperature dependence of the inverse resistance (an analogue of the conductivity for homogeneous samples with the same dimensions) has been estimated to be 0.19 eV for the samples with multi-walled carbon nanotubes and 0.62 eV for the samples with bound biochar.
- Saturation effect for dependence of the electrical conductivity of planar oriented nematic liquid crystal 6CB on the concentration of Cu7PS6 nanoparticlesPublication . Kovalchuk, O. V.; Studenyak, I. P.; Izai, V. Yu; Rybak, S. O.; Pogodin, A. I.; Kopčanský, P.; Timko, M.; Gdovinova, V.; Mariano, José; Kovalchuk, T. M.The influence of Cu7PS6 nanoparticles with the average size 117 nm on the dielectric properties of planar oriented nematic liquid crystal 6CB has been investigated within the frequency range 10(1) ...10(6) Hz and at the temperature 293 K. It has been shown that when changing the concentration of nanoparticles within the range 0 to 1 wt.%, the conductivity of the liquid crystal changes stronger than its dielectric permittivity. It has been shown that the electrical conductivity increases monotonously with increasing the concentration of nanoparticles. However, for this dependence a saturation effect is observed. The mechanism of this effect was proposed.