Conducting polymer-matrix composites containing carbon filaments of submicron diameter

Short carbon filaments catalytically grown from carbonaceous vapor and of diameter 0.2 μm and aspect ratio>1000 were found to be a more effective filler than comparably short pitch-based carbon fibers of diameter 10 μm and aspect ratio ≤300 in producing electrically conducting polyether sulfone (PES) matrix composites. The PES composite containing 7 vol.% filaments exhibited an electrical resistivity of 7.6 Ω.cm, an electromagnetic interference shielding effectiveness of 29 dB at 1-2 GHz, a thermal conductivity of 0.27 W/(m. °C), and a tensile strength of 42 MPa. Although the filaments gave composites of superior electrical properties compared to the fibers, they gave composites of inferior mechanical properties due to the poor filler-matrix bonding and the larger filler-matrix interface area at the same filler volume fraction. The superior electrical properties is attributed to the large number of contacts among the filaments due to their large aspect ratio. This paper also provides a process for dispersing the submicron filaments in a thermoplast.