Synergistic carbon nanotube ＋ carbon-coated iron nanoparticle polymer composites: Electrical, magnetic, and mechanical properties

Composite multifunctionality enabled by nanofiller modification has been widely explored in diverse applications. To date, work in this area has focused overwhelmingly on polymers modified with only a single type of nanofiller. Even studies that use more than one type of filler generally do so in order to achieve just a single type of multifunctionality—for example, modification with a combination of carbon nanotubes (CNTs) and graphene for higher electrical conductivity. Much less work has been done in the area of modifying polymers with multiple nanofiller types having dissimilar properties. To that end, we modify a representative polymer (epoxy) with a combination of multi-walled (MW)CNTs and carbon-coated iron nanoparticles (CCFeNPs). These phases give rise to combined electrical and magnetic properties in the MWCNT ＋ CCFeNP composite. DC and AC conductivity, permittivity, permeability, elastic modulus, and piezoresistive gauge factor were measured for varying relative concentrations of MWCNTs and CCFeNPs. Synergistic effects were observed, such as higher electrical conductivity and magnetic permeability in MWCNT ＋ CCFeNP composites. More specifically, composites containing 0.4 wt% MWCNT ＋ 0.1 wt% CCFeNP increased in DC conductivity by 0.5-0.6 S/m compared to 0.5 wt% MWCNT-only specimens. Furthermore, 0.1 wt% MWCNT ＋ 0.4 wt% CCFeNP composites showed a magnetic saturation increase of 1.66 × 10⁻⁴ emu/cm${}^3$ over 0.5 wt% CCFeNP-only composites.