Exceptional microwave absorption in soft polymeric nanocomposites facilitated by engineered nanostructures

Abstract

In this study, we present soft nanocomposites consisting of polycarbonate (PC) and poly styrene-co-acrylonitrile (SAN) that exhibit exceptional microwave absorption (ca. 91.1%) with a high attenuation constant. The blends containing multiwalled carbon nanotubes (MWNTs) and nickel nanoparticles nucleated on partially reduced graphene sheets (rGO–Ni) showed a high shielding effectiveness of −48 dB at 18 GHz. The ultra-small nickel nanoparticles, with average diameter of 5–8 nm, were uniformly decorated on the surface of rGO, providing pathways to disperse ferromagnetic nanoparticles in soft nanocomposites, which otherwise often suffer secondary agglomeration during processing. While synthesizing rGO–Ni, graphene oxide (GO) sheets were effectively reduced, manifesting enhanced electrical conductivity and effective charge transport in the nanocomposites. This was also facilitated by the uneven distribution of nanoparticles in the bi-phasic blend, thereby offering heterogeneous dielectric media and more interfaces that result in multiple scattering within the nanostructures. The underlying mechanism of attenuation, with the help of complex microwave properties, total losses, skin depth and attenuation constant in a broad frequency range (8–18 GHz) is systematically discussed. In addition, blends containing engineered nanostructures showed 1.5-fold higher storage modulus, compared to neat blends, as inferred from the dynamic mechanical thermal analysis (DMTA). Therefore, this study demonstrates an effective way to develop lightweight, soft and high performance microwave absorbers at relatively smaller fractions of nanoparticles for applications such as EMI shielding enclosures.