Speaker
Description
Polymer composites with inorganic fillers are highly valued for their unique properties and applications in areas such as protective systems, permanent magnets, magnetic delivery, microelectronics, and biomedicine. Recent studies suggest that using combined fillers, like nanocarbon and inorganic particles (e.g., magnetic oxides, barium hexaferrite, and other ferrites [1]), is a promising approach for developing advanced materials with exceptional properties.
In this work, composite materials based on epoxy resin (Larit$285$) with a combined filler of graphite nanoplates (GNP) /ferrites (CuFe$_2$O$_4$, NiFe$_2$O$_4$, and CoFe$_2$O$_4$) and multiwalled carbon nanotubes (MWCNT) /ferrites were manufactured and investigated. The content of nanocarbon varied from $2$ wt.$\%$ to $5$ wt.$\%$, and ferrites content was $20$ wt.$\%$. The electrical resistivity of the investigated composites was measured by the standard methods in DC mode at $T=77-293$ K; the frequency dependencies of microwave permittivity $\varepsilon(f)$ and permeability $\mu(f)$ were measured with E$4991$B Impedance Analyzer (Keysight Technologies, USA) in the frequency range $1-500$ MHz.
The experimental temperature dependences of the electrical resistance of nanocarbon/ferrite epoxy composites are explained in terms of the change in the temperature coefficient of resistance (TCR), the nature of which is determined by the change in the electrical transport mechanism in the material:
$$ TCR =\frac{1}{R}\frac{dR}{dT}. $$
The investigated composites GNP/ferrite and MWCNT/ferrite are characterized by different types of temperature dependence of electrical resistance, with a positive or a negative TCR, depending on which of the temperature-dependent processes are predominant.
AC electrical conductivity for investigated composites was determined as:
$$ \sigma_{AC}(f) = 2\pi f\varepsilon_{0}\varepsilon_{r}^{\prime}$$
The differences in the obtained $\varepsilon(f)$, $\mu(f)$, $\sigma_{AC}(f)$ dependences for nanocarbon/ferrite composites with different types of fillers are discussed.
Acknowledgments
The work was funded by the Ministry of Education and Science of Ukraine, grants 24BF051-01M (0124U001654), 24BF051-04, and by the National Research Foundation of Ukraine NRFU2023-03/193.
References
[1] R. Kumar et al., “Recent progress on carbon-based composite materials for microwave electromagnetic interference shielding,” Carbon, vol. 177. Elsevier BV, pp. 304–331, Jun. 2021. https://doi.org/10.1016/j.carbon.2021.02.091
