Dielectric behaviour and magnetic permeability of epoxy composites with nanocarbon and glass spheres

Composite materials (CMs) engineered with specific electrical, magnetic, and dielectric characteristics represent a promising class of functional materials for advanced technological applications. The aim of the work is to determine the effect of the size of glass spheres, their concentration, their interaction with nanocarbon and glass spheres (GS) partially coated with FeNi on the dielectric and magnetic properties in the frequency range of 1–500 MHz. Glass spheres were used with different diameters of 60, 100–200 and 600–800 ?m. The concentration of GSs was of 30 or 50 wt %. Multi-walled carbon nanotubes (MWCNTs) or graphite nanoplatelets (GNPs) were used as nanocarbon fillers. The dielectric and magnetic permittivity measurements were performed using a Keysight E4991B Impedance Analyzer within the frequency range of 1–500 MHz. The electrical resistance was measured with a Hiresta-UX MCP-HP800 system. It was found that the frequency dependences of the ?? for all investigated composites – both binary and ternary – exhibit a monotonically decreasing behavior. Such a trend is typical for polar materials, in which dipolar polarization fails to follow the alternating electric field at higher frequencies. It was found that in the two-phase composite 30 % GS+L285, the highest value of ?'(f) is observed when the glass spheres have the smallest diameter of 60 µm. Small GSs create much more interfacial surfaces (because their number is greater) in the polymer, so the number of polarization centers increases and ?? is higher. We found that the highest values of ??(f) were observed for the composite 5 % GNP+50 % GS (100–200 µm)+L285. Larger glass spheres in CMs with GNP contribute to better dispersion, less aggregation, more efficient orientation of graphite nanoplatelets and, as a result, higher interfacial polarization, which leads to an increase in ?'. The resistivity of this composite material is almost 7 orders of magnitude smaller than CM with a diameter GSs of 60 ?m. It was found that the values of ?? are the highest for the two-phase reduced FeNi(GS)+L285 composite material, decreases from 1.25 to 1.21. A slight increase in ?? for CMs is attributed to partial metal coating of the glass spheres and interactions at the filler–polymer interface; however, these effects are insignificant. The values of ?? ? 0 indicate that all fabricated samples are weakly magnetic.