Mechanical Properties of Stacked Cup Carbon NanofibersGavin McFarland, M.Sc., Northwestern University, 2011.
Major Professor: Dr. Horacio D. Espinosa.
Natural composites, such as nacre and bone, have very high toughness thanks to the rupture of noncovalent secondary bonds between chain segments of the organic phase. The rupture of these “sacrificial” bonds dissipates a great deal of energy while leaving the primary covalent bonds unbroken even at large strains. Stacked cup carbon nanofibers (CNFs) – helically coiled graphene ribbons with graphitic spacing between adjacent layers – have been shown to mimic that behavior through rupture of the π-π interactions between layers without harming the integrity of the graphene ribbon. In order to measure the mechanical properties of these CNFs, a tensile test was carried out in-situ SEM by affixing a CNF between a nanomanipulator probe and an AFM cantilever. Analysis difficulties forced several approximations to be used in order to obtain stress-strain data, and the modulus was computed to be around 3 GPa, though this likely undersells the true value by as much as three times. Furthermore, the CNF experienced brittle failure with no sign of any unraveling due to a stress concentration at the tip of the probe.