Armadillo shell-inspired carbon nanotubes-epoxy composites developed using 3D printing for electromagnetic interference shielding

Our study introduces a novel approach of preparing multiwall carbon nanotubes-epoxy nanocomposites with unique geometric structures inspired by the nine-banded armadillo shell. Through the use of steriolitheography (SLA) resin 3D printing and silicone molds, three hexagonal geometric designs are fabricated. The three geo- metric designs are: hexagonal structure (Hex), hexagonal pyramid with a flat tip (HF), and hexagonal pyramid with a pointed tip (HP). Small concentrations of carbon nanotubes (CNTs) ranging from 0 wt % to 0.75 wt % are incorporated in the epoxy matrix to create specimens representing all geometries, and the electromagnetic interference (EMI) shielding properties of the novel designs are compared with flat specimens with no geometric structure. This innovative method results in creating nanocomposites with architecture structures that exhibit significantly enhanced electrical conductivity and EMI shielding properties in the X-band frequency range. To ensure a fair comparison of the effect of geometrical designs on shielding properties, and to account for the effect of weight, normalized shielding values by the relative volume are calculated. The results indicate that the hexagonal pyramid geometries of 0.75 wt % CNTs-epoxy demonstrate the highest normalized shielding prop- erties compared to the flat-epoxy. Specifically, the HF and HP structures exhibit a 3.5-fold increase in shielding effectiveness, a 2.2-fold increase in reflectivity, and a remarkable 6.5-fold increase in absorptivity. While the dominant mechanism for shielding is reflection, the material exhibits a lossy behavior at higher concentrations of the high aspect ratio CNTs. Most notably, the HF and HP geometries demonstrate a constant shielding behavior across the entire frequency range, providing an added benefit compared to the less effective flat and hexagonal geometries.To further validate our findings, full-wave simulations are performed. A very good agreement between the simulated and experimental EMI shielding properties is achieved with a maximum percentage difference of only 15.8 % between simulated and experimental shielding effectiveness. Our novel approach of utilizing SLA additive manufacturing for advanced geometrically structured nanocomposite shows promise for developing advanced EMI shielding materials and overcoming limitations and defects of fused deposition molding, allowing for the production of intricate designs with high accuracy.