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Carbon nanotube/carbon (CNT/C) composites show potential for lightweight structural materials and non-metal electrical conductors for aerospace, military, and other industries where the combination of lightweight, high strength and excellent conductivity are required. Numerous research attempts have been reported to fabricate CNT/C composite focusing on high CNT alignment and dense carbon matrix. However, simultaneous improvements for mechanically strengthening and electrically improving properties of strength and conductivity in materials still presents a great challenge. In this study, pyrolyzed polydopamine (py-PDA) with selected surface treatments is introduced as an interface enhancer between CNTs and carbon matrix. Due to the presence of py-PDA, the effective physical interlocking and conductive pathways are rebuilt at the interface area between CNTs and carbon matrix, resulting in better load transfer and electron transport. The CNT/py-PDA/C composite fibers demonstrated remarkable improvements in electrical conductivity (2.1 × 103 S cm-1) and tensile strength (up to 727 MPa), which should prove to be vastly advantageous as compared to the previously reported CNT/C composites. The outstanding thermal stability of fully carbonized materials is also an attractive feature. Coupled with scalable manufacturing methods, these integrated characteristics of CNT/py-PDA/C composite fiber can potentially have broad applications for lightweight structural materials and non-metal conductors. [ABSTRACT FROM AUTHOR]

The detailed microstructure and failure modes of highly-aligned carbon nanotube (CNT) based composites have not been adequately studied due to a lack of high-resolution microscopy and the misunderstanding of nanotube interfacial bonding. In this work, high concentration (50-60 wt%) CNT composites with a measured alignment fraction of up to 0.93 are fabricated by mechanical stretching. The microstructure analysis by SEM showed evidence of failure due to nanotube bundle telescoping, interlayer separation, pullout, and folding. The relatively weak CNT/CNT and CNT/resin interactions are further studied by imaging of the bundle nanostructure using TEM analysis which revealed unique geometrically constrained self-assembly and packing of flattened and aligned CNTs. The CNTs in bundles were collapsed and preferred to form surface-to-surface stacking and shoulder-to-shoulder assemblies. MD simulations of 8 nm diameter nanotubes predicted a density of 0.665 and 1.820 g/cm3 for round and flattened nanotubes respectively. Comparing predicted densities to measured densities indicates that the samples are highly dense, with a very low void volume fraction and a large percentage of flattened CNTs. This insight into flattened and aligned CNTs has the potential to realize microstructures with the long-range order, low defect density and ordered crystalline CNT packing that are essential for fully translating CNT mechanical properties into high-performance composite materials. [ABSTRACT FROM AUTHOR]