Dielectric spectroscopy and synergistic effects in epoxy composites filled with multi‐walled carbon nanotubes and carbon‐coated copper nanoparticles

Abstract The electromagnetic properties of epoxy‐based composites filled with carbon‐coated copper (Cu@C) nanoparticles and multi‐walled carbon nanotubes (MWCNTs), along with hybrid MWCNT/Cu@C/Epoxy systems containing varying concentrations of nanoinclusions, were systematically investigated across multiple frequency and temperature ranges. Measurements were conducted in the low‐frequency range (20 Hz–1 MHz) and over a temperature span of 40–500 K, as well as in the microwave frequency range (26–37 GHz) at room temperature. The percolation threshold was identified at approximately 2.5 vol% for composites containing only Cu@C nanoparticles and at 0.3 vol% for composites with MWCNTs. Notably, the hybrid MWCNT/Cu@C/Epoxy composites exhibited significantly enhanced electromagnetic properties compared to those of the single‐filled systems. At room temperature, an epoxy composite containing 5 vol% Cu@C and 1 vol% MWCNT exhibits a conductivity of approximately 4 × 10⁻² S/m, which increases by nearly two orders of magnitude following a thermal cycle up to 500 K. The total electromagnetic interference (EMI) shielding effectiveness in the 26–37 GHz range was measured between 4 and 9 dB, indicating the material's promising potential for attenuating microwave noise. Dynamic mechanical analysis (DMA) results revealed that increasing the MWCNT content improved the storage modulus of the composites but led to a reduction in the glass transition temperature (T_g), which was observed to range between 40 and 50°C. The incorporation of MWCNTs and Cu@C nanoparticles into epoxy matrices offers a promising approach for the development of lightweight multifunctional composites with superior electrical, mechanical, and EMI shielding properties. Highlights The percolation threshold in MWCNT/Epoxy composites is 0.3%. The percolation threshold in Cu@C/Epoxy composites is 2%. The conductivity value of MWCNT/Cu@C/Epoxy composites is around 4 × 10⁻² S/m. The total shielding effectiveness in the Ka‐band range between 4 and 9 dB. Glass transition temperature of MWCNT/Cu@C/Epoxy is between 40 and 50°C.