Strengthened magnetic epoxy nanocomposites with protruding nanoparticles on the graphene nanosheets

Magnetic graphene (Gr) nanocomposites (Gr nanosheets coated with iron core iron oxide shell nanoparticles, named Gr/Fe@Fe₂O₃) have successfully served as nanofillers for obtaining magnetic epoxy resin polymer nanocomposites (PNCs) to be compared with the epoxy nanocomposites with pure graphene. The effects of nanofiller loading levels on the rheological behaviors, thermal stability, thermo-mechanical, tensile mechanical properties, electrical conductivity and magnetic properties were systematically studied. A reduced viscosity was observed in the 1.0 wt% Gr-epoxy resin liquid nanosuspensions and the viscosity was increased with further increasing the Gr loading. In the TGA test, although the introduction of both nanofillers caused lower onset decomposition temperature of the PNCs, the Gr/Fe@Fe₂O₃ was found to favor the char formation from the epoxy resin. The enhanced char residue was also observed during the flammability tests. The dynamic storage and loss modulii were studied together with the glass transition temperature (T_g) obtained from the peak of tanδ. The tensile strength observed in the PNCs with 1.0 wt% Gr/Fe@Fe₂O₃ is 58% higher than that of the pure epoxy, and was attributed to the high stiffness of Gr. Both nanofillers could increase the electrical conductivity of the epoxy matrix. The magnetic properties of the PNCs with Gr/Fe@Fe₂O ₃ are studied and the value of coercivity (Hc) is observed inversely proportional to the loading of Gr/Fe@Fe₂O₃ in the PNCs due to the decreased interparticle dipolar interaction, which arises from the enlarged nanoparticle spacer distance for the single domain nanoparticles. Finally, the increased real permittivity observed in the PNCs is attributed to the interfacial polarization.