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Random networks comprised of millimeter-long multi-walled carbon nanotubes (CNTs) have shown unique microstructure change mechanisms under uniaxial strain. These networks can be modified into highly aligned microstructures from strain-induced plastic deformation. Applying a treatment consisting of an uncured resin as a load transfer enhancement medium leads to a dramatically increased degree of alignment and final mechanical properties of the CNT networks. The structural evolution of the CNT networks includes different modes: de-bundling, elongation to reduce waviness, sliding friction, and packing for self-assembly into large bundles. The high ductility of the treated networks, which allows the network to achieve high degrees of strain-induced alignment is mainly because the extra high aspect ratios of the individual CNTand their bundles as well as enhanced load transfer. High aspect ratio causes high degrees of entanglement and locking points between the nanotubes in the random network, which are critical to provide adequate nanotube to nanotube load transfer for ductile deformation and lead to substantially increased CNT alignment during mechanical stretching. The classical strain strengthening mechanisms used in metals and polymers such as strain hardening and crystallization of long molecular chains are discussed and compared to CNT network deformation mechanisms. The CNT network strain hardening parameter n value is as high as 0.65, over three times that of annealed low-carbon steel and more than four times of polycarbonate plastics. Strength coefficient K values for the CNT network also show high values up to roughly 450 MPa, comparable to that of annealed magnesium alloys. The results show how the high degree of alignment of CNT networks and strain strengthening can be achieved through simple uniaxial strain and load transfer medium.

This paper reports on a study of carbon nanotube (CNT) thin film, or buckypaper (BP), integrated into carbon fiber (CF) prepreg composites to create hybrid composite materials with high CNT content. The autoclave process of manufacturing hybrid composite laminates was investigated to gain an understanding of nano/micro dual-scale resin flow characteristics. The study found that resin bleeding along the through-thickness direction was inhibited due to extra-low permeability and high resin absorbing capacity of the BP. Resin matrix-impregnated BP layers were much thicker than dry pristine BP due to high resin absorbency and swelling effects. The BP/unidirectional carbon fiber (UD-CF) hybrid composites with local fiber volume fraction of 61.46 vol% in CF ply and local CNT volume fraction of 26.57 vol% in BP layer, had a tensile strength of 2519 AE 101 MPa and modulus of 149 AE 18 GPa. The dramatic improvements in both in-plane and through-thickness electrical conductivities demonstrate potential for both structural and multifunctional applications of the resultant hybrid composites.

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High‐performance carbon‐nanotube‐based thermoplastic composites are synthesized through in situ polymerization of cyclic butylene terephthalate (pCBT) on aligned carbon nanotube buckypaper. The initial results show that the buckypaper/pCBT composites have a tensile strength of approximately 600 MPa and a modulus of 96 GPa due to the aligned nanotubes in the composite acting as a framework and the in situ polymerization resulting in increased interfacial interactions between the pCBT chains and nanotubes. The buckypaper/pCBT composites also demonstrate significantly improved thermal (70 W m−1 °C−1) and electric conductivities (526 S cm−1), as well as thermoelectric power (Seebeck coefficient of 64 μV °C−1). With low mass density, these combined excellent multi‐properties indicate that the composites can act as multifunctional materials in numerous applications.

Functionalization is critical for improving mechanical properties of carbon nanotubes (CNTs)/polymer nanocomposites. A fundamental understanding of the role of the CNT/polymer interface and bonding structure is key to improving functionalization procedures for higher mechanical performance. In this study, we investigated the effects of chemical functionalization on the nanocomposite interface at atomic resolution to provide direct and quantifiable information of the interactions and interface formation between CNT surfaces and adjacent resin molecules. We observed and compared electronic structures and their changes at the interfaces of nonfunctionalized and functionalized CNT/polymer nanocomposite samples via scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) spectrum imaging techniques. The results show that the state of sp2 bonding and its distribution at the CNT/resin interface can be clearly visualized through EELS mapping. We found that the functionalized CNT/polymer samples exhibited a lower fraction of sp2 bonding and a lower π*/σ* ratio compared with the nonfunctionalized cases. A good correlation between near-edge fine structures and low-loss plasmon energies was observed.

Front Cover: In‐situ polymerization of cyclic butylene terephthalate (pCBT) on aligned carbon nanotube (CNT) buckypaper generates thermoplastic composites with favourable properties. pCBT encapsulates the CNT network with strong interfacial adhesion, allowing for efficient load transfer from the polymer matrix to the nanotubes. Cover image shows the pCBT‐covered CNTs, before and after fracture from tensile testing. Further details can be found in the article by Z. Li,* R. Downes, Z. Liang on page 292.