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

Biswas, Sourav, Panja, Sujit S., Bose, Suryasarathi
Journal of physical chemistry 2018 v.122 no.34 pp. 19425-19437
absorption, carbon nanotubes, cobalt, electronic equipment, hysteresis, impedance, industry, iron, iron oxides, magnetism, nanoparticles, nickel, polymer nanocomposites, researchers, synergism, thermoplastics
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 multiwalled 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. MWCNTs, 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 π-electrons in MWCNTs suggest a synergistic effect from both the phases. As a result, −31 dB shielding effectiveness is observed in the case of Fe₃O₄ 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.