Broadband Electromagnetic Response and Enhanced Microwave Absorption in Carbon Black and Magnetic Fe3O4 Nanoparticles Reinforced Polyvinylidenefluoride Composites

High-efficiency Electromagnetic Interference (EMI) shielding materials are essential in the harsh environment created by unwanted electromagnetic (EM) signals. In this work, polyvinylidenefluoride (PVDF) composites reinforced with magnetic Fe3O4 nanoparticles and cost-effective conducting carbon black (CB) were derived by a solution mixing and coagulation method. Coagulation is found to be an effective method to fabricate uniform composites of materials having higher tendency to form aggregates. The three-dimensionally extending conducting network created by CB and the hopping electrons from Fe3O4 result in high electrical conductivity of PVDF/CB/Fe3O4 composites (PCF). The permittivity, permeability and impedance spectra in the 10 MHz-1 GHz broadband region indicate that dielectric loss is dominating over magnetic loss and is attributed to the collection of a large number of capacitive regions at the interfaces formed by CB and Fe3O4, which results in the enhanced interfacial polarization losses in PCF composites. The composites exhibit EMI shielding effectiveness (EMI SE) greater than 20 dB and their shielding mechanisms involve dielectric losses, magnetic losses and their synergistic interaction. The matching input impedance of the composites allows the radiations to enter into the material and it undergoes multiple internal reflections at the interfaces and the energy of the internally reflected radiation is subsequently absorbed by CB. These different mechanisms result in an absorption dominated EMI shielding with a total EMI SE of 55.3 dB (99.9997% of shielding) for PCF-40 composite having thickness 2 mm and an average skin depth of 0.37 mm in the X-band microwave region.