Studies of the properties of nanocomposites reinforced with vapor-grown carbon nanofibers (VGCFs) can be found throughout the literature. Electrical, mechanical, viscoelastic, and rheological properties are just a few of the characteristics that have been well discussed. Although these properties depend on morphology, morphological characterization is rare. Due to its 2-dimensional nature, microscopy is of limited value when analyzing network morphologies. This work will show how the characterization of the three-dimensional geometry and network formation of VGCFs can be determined using ultra-small angle scattering techniques.

Ultra-small angle x-ray and neutron scattering (USAXS and USANS) were used to characterize the morphology of carbon nanofibers suspended in epoxy. Using a simplified tube model, we estimate the dimensions of suspended fibers. The assumption of tubular fibers accounts for the increased surface area observed with USAXS that is not accounted for using a solid rod model. Furthermore, USANS was used to search for a structural signature associated with the electrical percolation threshold. USANS extends to longer dimensional scales than USAXS, which measures a smaller range of momentum transfer.

To determine the electrical percolation threshold, AC impedance spectroscopy was employed to verify that an electrically conductive, percolated network forms at VGCNF loadings of 0.8% < CNF wt% < 1.2%. These values correlate with the USANS data, where a morphological transition is seen at ~1.2% loading.