The effect of filler distribution on electromagnetic properties of nanocarbon/magnetic particles/polymer composites

The type of multi-component fillers and their spatial distribution in conductive polymer-based composites greatly influenced their electrical properties, electromagnetic shielding efficiency (SE), and absorption capability, which require a deep understanding of how these properties improve with changes in the phase composition, content, and distribution of these fillers in the composite. In this study, three-phase polymer composite materials (CMs) with random (epoxy-based) and segregated (polyethylene-based) distribution of nanocarbon (graphite nanoplatelets GNP and carbon nanotubes CNTs) and magnetic (Fe and Co3O4) fillers have been developed. It was found that permittivity εr′ in the frequency range (40–60 GHz) increases sufficiently with the nanocarbon content and their values are slightly higher for random GNP-filled CMs (εr′=10–15 for 3–5 wt. % GNP) compared to CNT-filled CMs and much higher compared to segregated CMs (εr′=4–7 for 3–5 wt. % of nanocarbon). Dielectric loss tangent tanδ is increased with the nanocarbon content (especially for Fe-filled CMs) and sufficiently higher in segregated CMs compared to similar random composites. These enhanced tanδ values correlate with higher electromagnetic shielding efficiency due to absorption of segregated nanocarbon/magnetic/polyethylene CMs, for example, SEAd ≈ 18–23 dB/mm for 5 wt. %GNP. The most preferable for microwave absorption are random and segregated CMs with 2–3 wt. % GNP/30 wt. % magnetic filler: RLmin = −(27–35) dB, effective absorption bandwidth (EAB) Δf10dB=11.5–12.5GHz at a sample thickness of 0.5–0.7 mm. In CNT-based segregated CMs, |RLmin| and EAB values are lower compared with GNP-based CMs. The ability to manipulate these characteristics is important for obtaining good shielding and absorptive properties in the microwave range of electromagnetic radiation.