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The severe challenge in ordering carbon nanotubes (CNTs) has become one of the key obstacles in developing high performance CNT fibers. Herein, a nondestructive straightening and multifunctionalization strategy is developed based on an interfacial-bubbling-induced expansion to CNT networks. By activating an electrolysis process in an acid solution, hydrogen bubbles are generated and evolved within the interior of CNT network, leading to an extremely large and uniform expansion, with the lateral size increased by more than two orders of magnitude. The expansion is found to be governed by a force balance between the liquid pressing, surface tension of bubble, and confining force from the network. The expanded CNT networks can be converted into highly aligned and densified fibers with a tensile strength up to 5.18 GPa, after continuous stretching and densification. They are also excellent scaffolds for multifunctional composites. By in situ impregnating polyethylene glycol during the expansion, robust composite fibers with the abilities of electro-thermal conversion and phase change energy storage are produced. [Display omitted] • CNT assemblies can be nondestructively expanded by a process of interfacial bubbling. • The expansion makes it possible to fully straighten the interior wavy nanotubes. • Superstrong or multifunctional composite fibers are spun using the expanded assembly. [ABSTRACT FROM AUTHOR]

High temperature thermoplastics are gaining popularity due to their superior toughness and durability. For a new member in the polyaryletherketone (PAEK) family, polyetherketoneketone (PEKK) has shown the highest melting temperature, up to 380 °C. Meanwhile, it requires a high temperature to improve the interfacial shear strength (IFSS) between PEKK and a fiber, toward advanced thermoplastic composites. Owing to the strong Joule heating in carbon nanotube (CNT) fibers, a more efficient strategy is designed to enhance the IFSS. Under the electro treatment, the surrounding PEKK starts the melting at the fiber surface, and even impregnates into the CNT assemblies. As a result, the interfacial interaction can be remarkably enhanced. The highest IFSS is up to 80.4 MPa for the electro-treated interface between a CNT fiber and PEKK, higher than the thermal-treated IFSS (52.5 MPa) and that between an aramid fiber and PEKK (59.8 MPa). [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) fibers are merged into a robust larger-diameter yarn by using an adhesion agent of polyethylenimine (PEI). As compared to poly(vinyl alcohol) and epoxy, PEI molecules can unite neighboring CNT fibers by constructing a strong inter-fiber adhesion, owing to their high mobility to soften the fiber surface. The merged yarn inherits fully the tensile strength and toughness from the single fiber, remains electrically conducting, and can be stably used up to 180 ° C even in O 2 . It also exhibits high mechanical performances under various application conditions, such as bending, pressing, twisting, and rubbing. Image 1 • Carbon nanotube fibers are merged (multi-plied) into a large-diameter yarn. • The low viscosity of polyethylenimine induces efficient merging between the fibers. • The multi-plied yarn can be stronger than the individual fiber. [ABSTRACT FROM AUTHOR]

The way how carbon nanotubes (CNTs) are assembled together determines the utilization efficiency of mechanical property in their macroscopic assembly materials. For one-dimensional (1D) assemblies, CNTs are often assembled under drawing and twisting into a fiber structure with a twist angle. In this study, an untwisted 1D assembly, CNT strip, is introduced, inside which the CNTs are not only aligned but also overall parallel to strip axis. Due to the shielding effect of the twisted fiber surface, the interior of CNT fiber is loosely packed, and the fiber is more stretchable and hard to become stiff. On the contrary, CNT strip with high straightness or undirectionality can utilize the CNT's mechanical property much more efficiently, as reflected by its higher strength and modulus. These insights can guide different applications of CNT fibers and strips in textile. [ABSTRACT FROM AUTHOR]

The fiber-to-matrix interfacial shear strength (IFSS) plays a key role in building up composite structures using carbon nanotube (CNT) fibers. Originating from the assembly characteristics of CNT fiber, the IFSS strongly depends on the fiber's twisting level and densification level. Furthermore, there are rich ways to modify the fiber surface and thus enhance the IFSS, including the surface modification, the infiltration of matrix resin, and the introduction of silane coupling agent. As a new feature different from carbon fibers, these treatments either change the fiber's surface or form an interphase inside rather than around the fiber, and extend the common concept of surface sizing. [ABSTRACT FROM AUTHOR]

A carbon nanotube (CNT) fiber is formed by assembling millions of individual tubes. The assembly feature provides the fiber with rich interface structures and thus various ways of energy dissipation, as reflected by the nonzero loss tangent (>0.028-0.045) at low vibration frequencies. A fiber containing entangled CNTs possesses higher loss tangents than a fiber spun from aligned CNTs. Liquid densification and polymer infiltration, the two common ways to increase the interfacial friction and thus the fiber's tensile strength and modulus, are found to efficiently reduce the damping coefficient. This is because the sliding tendency between CNT bundles can also be well suppressed by a high packing density and the formation of covalent polymer cross-links within the fiber. The CNT/bismaleimide composite fiber exhibits the smallest loss tangent, nearly the same as that of carbon fibers. At a higher level of the assembly structure, namely a multi-ply CNT yarn, the interfiber friction and sliding tendency obviously influence the yarn's damping performance, and the loss tangent can be tuned within a wide range, similar to carbon fibers, nylon yarns, or cotton yarns. The wide-range tunable dynamic properties allow new applications ranging from high quality factor materials to dissipative systems. [ABSTRACT FROM AUTHOR]

The spun carbon fibers were fabricated from multi-walled carbon nanotubes by a drawing and twisting method. The thermionic field emission behavior of the carbon fibers was investigated as a function of applied heating power P and field emission voltage V. The thermal field emission turn-on voltage and threshold voltage are found at electric field E = 2.6 V/μm and E = 3.0 V/μm, respectively. It is found that the emission current density, dominated by the field emission mechanism, reached up to J = 1.3 A/cm ( P = 0 W) and J = 3 A/cm ( P = 2.0 W) at an emission field of E = 5.0 V/μm. The lifetime with respect to heating power P, exhibiting about 45 h continuous luminescence under a constant P = 0.8 W, was investigated in the spun carbon fibers. Our results indicate that high-strength carbon fibers show good performance as a thermionic field emission source. [ABSTRACT FROM AUTHOR]

The performance of carbon nanotube (CNT) fibers is limited by the intertube characteristics. Here we report a direct method of curing to improve mechanical properties of poly(amic acid)-infiltrated fibers. After curing at 190 °C for 60 min the fibers composed of double- and triple-walled CNTs, their strength is stably improved by 30.3%, from 1.58 to 2.06 GPa. The enhancement arises from the increase in shear stress between tube surfaces, by measuring the static frictional force of CNT fibers. Due to the existence of CNTs, the imidization temperature of polyimide drops greatly from 218 to 157 °C. [ABSTRACT FROM AUTHOR]

High performance nanocomposites require well dispersion and high alignment of the nanometer-sized components, at a high mass or volume fraction as well. However, the road towards such composite structure is severely hindered due to the easy aggregation of these nanometer-sized components. Here we demonstrate a big step to approach the ideal composite structure for carbon nanotube (CNT) where all the CNTs were highly packed, aligned, and unaggregated, with the impregnated polymers acting as interfacial adhesions and mortars to build up the composite structure. The strategy was based on a bio-inspired aggregation control to limit the CNT aggregation to be sub 20-50 nm, a dimension determined by the CNT growth. After being stretched with full structural relaxation in a multi-step way, the CNT/polymer (bismaleimide) composite yielded super-high tensile strengths up to 6.27-6.94 GPa, more than 100% higher than those of carbon fiber/epoxy composites, and toughnesses up to 117-192 MPa. We anticipate that the present study can be generalized for developing multifunctional and smart nanocomposites where all the surfaces of nanometer-sized components can take part in shear transfer of mechanical, thermal, and electrical signals. [ABSTRACT FROM AUTHOR]

Abstract: Liquid infiltration is an efficient way to densify carbon nanotubes (CNTs) and was used to strengthen CNT fibres in the method of array spinning. Rather than the volatility, the dipole moment of solvent plays a more important role in determining the densification level. The fibres densified by highly polar but non-volatile solvents such as N,N-dimethylformamide, dimethyl sulphoxide, and N-methyl-2-pyrrolidone were 100–200MPa stronger than those by ethanol and acetone. Ethylene glycol is the most efficient solvent due to its two polar OH groups and improved the fibre strength to 1.45GPa. Long chain or cross-linked polymers like polyvinyl alcohol, polyimide, and bismaleimide (BMI) were introduced into CNT fibres by infiltration with aid of polar solvents. These polymers reinforced the fibres significantly, as they can connect non-neighboring CNTs and benefit the load transfer. The strongest CNT/BMI fibre was 2.38GPa in strength and 110GPa in modulus. [Copyright &y& Elsevier]

Abstract The enhanced interfacial interaction between carbon nanotubes (CNTs), and thus the promoted interfacial thermal transport (ITT), are keys to improve the efficiency of CNT-assembled thermo-functional devices and materials, including energy transmission medium and thermal interface materials. Here, by using the intriguing CNT fibers decorated with Au nanoparticles (NPs) as a promising platform, we attain to the underlying mechanism for the remarkably boosted ITT of CNT/Au/CNT contacts. The enhancement is ascribed to the NP-induced excitation of low-frequency phonon (LFP) modes in CNTs, a strong mechanism to redistribute LFP modes into the interfacial carbon atoms and then to activate a resonance with the LFPs of Au NPs, resulting in more heat transfer across the contact. Furthermore, the Au NP/CNT fiber also exhibits an enhanced interfacial electrical transport, owing to the extraction of highly degenerate electronic density of states near the van Hove singularities, and thus induces an equivalent p-type doping for the CNTs. The present study demonstrates a new strategy to develop multifunctional CNT fibers with enhanced electrical and thermal conductivities. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Electrical and thermal management in nanodevices by means of carbon nanotube is highly promising. One main challenge toward CNT-based nanoscale electrical and thermal management devices is the development of effective strategies for reducing the bundle–bundle interface resistance. Here we report a novel strategy, based on the densification of CNT bundles and the functionalization of inter-bundle interfaces for effectively enhanced interfacial electrical and thermal transport. The densification is realized by utilizing the local electrostatic cohesion; and the functionalization is realized by the interface-decorated functional groups. Experiments and theoretical analysis demonstrated obviously enhanced interfacial electrical and thermal conductance originates from: (1) local Coulomb electrostatic cohesion between CNT bundles due to surface-induced dipole moments. This effect can promote both electrical and thermal conductance nearly 2.8 times higher than non-functionalized counterpart. (2) Increased interfacial electron transport channels and thermal vibrations due to surface-decorated functional groups. This effect can bring about up to 75% and 95% improvement for thermal and electrical conductance, respectively. This study provides a new methodology for tunable operation of electrical and thermal properties at inter-bundle interfaces and guidance for design of CNT-based electrical and thermal management devices. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotube (CNT) fibers spun from CNT arrays were used as the reinforcement for epoxy composites, and the interfacial shear strength (IFSS) and fracture behavior were investigated by a single fiber fragmentation test. The IFSS between the CNT fiber and matrix strongly depended on the types of liquid introduced within the fiber. The IFSS of ethanol infiltrated CNT fiber/epoxy varied from 8.32 to 26.64MPa among different spinning conditions. When long-molecule chain or cross-linked polymers were introduced, besides the increased fiber strength, the adhesion between the polymer modified fiber and the epoxy matrix was also significantly improved. Above all, the IFSS can be up to 120.32MPa for a polyimide modified CNT fiber, one order of magnitude higher than that of ethanol infiltrated CNT fiber composites, and higher than those of typical carbon fiber/epoxy composites (e.g. 60–90MPa). Moreover, the composite IFSS is proportional to the tensile strength and modulus of the CNT fiber, and decreases with increasing fiber diameter. The results demonstrate that the interfacial strength of the CNT fiber/epoxy can be significantly tuned by controlling the fiber structure and introducing polymer to optimize the tube–tube interactions within the fiber. [Copyright &y& Elsevier]