Investigation of the interphase structure in polyamide 6–matrix, multi-scale composites

In this study, we investigated the dispersion of carbon nanotubes and the interphases formed around them in nanocomposites with a polyamide 6 matrix (with carbon nanotube reinforcement) and hybrid composites with the same matrix, reinforced with carbon nanotubes and carbon fibers. Small-angle neutron scattering (SANS) experiments showed that carbon fibers effectively increased the dispersion of the carbon nanotubes. The average size of the carbon nanotube aggregates were significantly smaller, but the reinforcement–matrix interface area was larger in the hybrid composites than in the nanocomposites. Nanotube dispersion had a significant effect on the crystalline structure; the X-ray diffraction patterns showed that in the hybrid composites, the crystallites grew epitaxially on the surface of the well-dispersed carbon nanotubes, which resulted in decreased average crystallite size. In the hybrid composites, the smaller crystallites inferred a larger rigid amorphous fraction in the matrix. The larger interphase fraction in the hybrid composites also led to better mechanical performance.