Mechanical and structural characterization of electrospun PAN-derived carbon nanofibers

The mechanical and structural properties of individual electrospun PAN-derived carbon nanofibers are presented. EELS spectra of the carbonized nanofibers shows the C atoms to be partitioned into ∼80% sp² bonds and ∼20% sp³ bonds which agrees with the observed structural disorder in the fibers. TEM images show a skin-core structure for the fiber cross-section. The skin region contains layered planes oriented predominantly parallel to the surface, but there are some crystallites in the skin region misoriented with respect to the fiber long axis. Microcombustion analysis showed 89.5% carbon, 3.9% nitrogen, 3.08% oxygen and 0.33% hydrogen. Mechanical testing was performed on individual carbonized nanofibers a few microns in length and hundreds of nanometers in diameter. The bending modulus was measured by a mechanical resonance method and the average modulus was 63 GPa. The measured fracture strengths were analyzed using a Weibull statistical distribution. The Weibull fracture stress fit to this statistical distribution was 0.64 GPa with a failure probability of 63%.