In situ build coaxial bilayer shell with decreasing conductivity from the surface of carbon nanotubes

To control the dielectric loss of polymer/carbon nanotube (CNT) composites, we developed coaxial double-layer coated CNTs to form a diminishing conductive gradient from the CNT center to its outside through a dual-functional polyaniline (PANI) interlayer. The conductive multiwalled CNTs were covered with a semiconductive PANI first shell through in situ redox polymerization with ferric chloride as the oxidizing agent; moreover, this agent is the precursor of the second iron hydroxide shell. The inorganic outer layer of iron hydroxides was directly coated on the PANI interlayer surface through in situ deposition method to obtain an insulating property. Depending on the conductivity that decreases from the inside to the outside of the core-shell structured CNT hybrids, the epoxy resin-based composites showed gradually reduced dielectric losses because the double-coating layers hindered the reunion and connection of conductive CNTs.