Physical Insight into the Mechanism of Electromagnetic Shielding in Polymer Nanocomposites Containing Multiwalled Carbon Nanotubes and Inverse-Spinel Ferrites

A surge in the usage of electronic devices has led to a new kind of problem; electromagnetic (EM) interference. In a quest toward providing effective shielding, which offers design flexibility, lightweight, and ease to integrate and embed, the right combination of materials needs to be synthesized and dispersed in a polymer matrix to design composites that can shield EM radiation. However, selection of nanoparticles from a vast library is quite challenging and, hence, this study attempts to provide a physical insight into the mechanism of shielding in polymer nanocomposites containing a conducting phase (here multi-walled carbon nanotubes, MWCNTs) and a magnetic phase [here inverse-spinel ferrites, MFe2O4 (M = Fe, Co, Ni)]. We adopted a biphasic co-continuous blend (consisting of polycarbonate and polyvinylidene fluoride) as the matrix to incorporate the conducting and the magnetic phases. MWENTs, which offer interconnected conductive fence, and ferrites, which provide magnetic dipoles that couple with incoming EM radiation, can absorb the incoming EM radiation. The detailed mechanistic insight regarding absorption of EM radiation reveals that high saturation magnetization, high consolidated loss, better impedance matching, higher attenuation constant, high hysteresis loss, and comparable eddy current loss help Fe3O4, compared to the other ferrites employed here, to effectively shield the EM wave in the X and Ku band frequency through absorption. In addition, better impedance matching, low skin depth, and enhanced dielectric and/or interfacial polarization losses because of pi-electrons in MWCNTs suggest a synergistic effect from both the phases. As a result, -31 dB shielding effectiveness is observed in the case of Fe2O4 and MWCNTs, which is 19% higher when compared with CoFe2O4 + MWCNT-containing blends and 24% higher when compared with NiFe2O4 + MWCNT-containing blends. Interestingly, when the nanoparticles are forced to localize in different components of the blends, the overall shielding efficiency enhances further because of their higher consolidated loss parameters. Hence, the mechanistic insight provided in this paper will help guide researchers working in this field from both academic and industry perspectives.