Properties Of Carbon Nanotube Yarns Research Articles

Effect of extreme mechanical densification on the electrical properties of carbon nanotube micro-yarns

We have explored the effect of high pressure post-treatment in optimizing the properties of carbon nanotube yarns and found that the application of dry hydrostatic pressure reduces porosity and enhances electrical properties. The CNT yarns were prepared by the dry-spinning method directly from CNT arrays made by the hot filament chemical vapour deposition (HF-CVD) process. Mechanical hydrostatic pressure up to 360 MPa induces a decrease in yarn resistivity between 3% and 35%, associated with the sample’s permanent densification, with CNT yarn diameter reduction of 10%–25%. However, when increasing the pressure in the 1–3 GPa domain in non-hydrostatic conditions, the recovered samples show lower electrical conductivity. This might be due to concomitant macroscopic effects such as increased twists and damage to the yarn shown by SEM imaging (caused by strong shear stresses and friction) or by the collapse of the CNTs indicated by in situ high pressure Raman spectroscopy data.

Enhancement of the mechanical and thermal transport properties of carbon nanotube yarns by boundary structure modulation

Carbon nanotubes (CNTs) exhibit extremely high nanoscopic thermal/electrical transport and mechanical properties. However, the macroscopic properties of assembled CNTs are significantly lower than those of CNTs because of the boundary structure between the CNTs. Therefore, it is crucial to understand the relationship between the nanoscopic boundary structure in CNTs and the macroscopic properties of the assembled CNTs. Previous studies have shown that the nanoscopic phonon transport and macroscopic thermal transport in CNTs are improved by Joule annealing because of the improved boundary Van-der-Waals interactions between CNTs via the graphitization of amorphous carbon. In this study, we investigate the mechanical strength and thermal/electrical transport properties of CNT yarns with and without Joule annealing at various temperatures, analyzing the phenomena occurring at the boundaries of CNTs. The obtained experimental and theoretical results connect the nanoscopic boundary interaction of CNTs in CNT yarns and the macroscopic mechanical and transport properties of CNT yarns.

Comprehensive Characterization of Structural, Electrical, and Mechanical Properties of Carbon Nanotube Yarns Produced by Various Spinning Methods.

A comprehensive characterization of various carbon nanotube (CNT) yarns provides insight for producing high-performance CNT yarns as well as a useful guide to select the proper yarn for a specific application. Herein we systematically investigate the correlations between the physical properties of six CNT yarns produced by three spinning methods, and their structures and the properties of the constituent CNTs. The electrical conductivity increases in all yarns regardless of the spinning method as the effective length of the constituent CNTs and the density of the yarns increase. On the other hand, the tensile strength shows a much stronger dependence on the packing density of the yarns than the CNT effective length, indicating the relative importance of the interfacial interaction. The contribution of each physical parameter to the yarn properties are quantitatively analyzed by partial least square regression.

Purification, structural evolutions, and electrical properties of carbon nanotube yarns processed via incandescent annealing

Incandescent annealing in high vacuum is investigated for the purification of carbon nanotube (CNT) yarns produced via the floating catalyst chemical vapor deposition (CVD) method. The existing chemical purification routes damage CNTs and often require CNT dispersion. As an alternative, thermal annealing in inert or vacuum atmospheres has proved to remove impurities alongside improving CNT graphitization. Current-induced incandescent annealing process (IAP) in high vacuum provides a scalable and efficient route for the purification of CNT structures in a matter of seconds compared to hours of thermal annealing, reducing time and energy by orders of magnitude. In this study, electrical properties of CNT yarns are correlated with the morphological changes of their structure resulted from the IAP. Three distinct resistivity ranges based on the IAP current were identified and the detailed chemical composition, structure, and temperature-dependent resistivity of their corresponding yarns were investigated. It is concluded that the transport mechanism in the CNT yarns changes dynamically and drastically with the removal of amorphous carbon, iron, sulfur, and reduction in chlorine content. The correlations between the chemical composition, structure, and resistivity of samples provide new insight into CNT doping mechanisms and can be utilized to improve the conductivity of commercially available CNT yarns.

One-Minute Joule Annealing Enhances the Thermoelectric Properties of Carbon Nanotube Yarns via the Formation of Graphene at the Interface

Interfaces in nanocarbon materials are highly important, as they determine the properties of carbon-based devices. In terms of carrier and thermal transport properties, the interfacial features are...

Improved Mechanical and Electrical Properties of Carbon Nanotube Yarns by Wet Impregnation and Multi-ply Twisting

Carbon nanotube (CNT) fibers, composed entirely of CNT bundles, have inferior mechanical properties as adjacent CNTs slide past each other when an external force is applied. Numerous surface coatings have been tried, but all these approaches have caused severe damage to the electrical properties of the resulting fibers. As a measure to address these problems, we present an effective method for the enhanced mechanical and electrical properties of CNT yarns by wet impregnation with a poly(vinylidene fluoride)/ionic liquid (PVDF/IL) composite and subsequent multiply twisting. Single twisting of three-ply yarns showed a superior electrical conductivity of up to 1500 S/cm, while braided twisting of pretwisted yarns exhibited excellent tensile performances, with a load capacity of 3.2 N, tensile strength of 12.7 g/de, and tensile strain of 35.2 %. The polarized Raman measurements confirmed the elevated CNT quality and high alignment of CNT bundles. The proposed approach of impregnated and twisted CNT yarns will lead to a variety of potential applications in sensors/actuators, e-textile devices, and fiber-shaped electrodes, which simultaneously requires ultra-light weight and good electrical and tensile properties.

Effect of twist on the electromechanical properties of carbon nanotube yarns

Twist is used in dry-spinning of carbon nanotube (CNT) yarn mostly to establish a high degree of association between the loosely bound CNT bundles. By doing so, the CNT yarn undergoes mechanical densification, which increases its strength and changes its electrical properties. The effect of twist on the elastic modulus, tensile strength, strain-to-failure, toughness and piezoresistivity was studied and discussed for CNT yarns subjected to uniaxial tension. Due to the interplay of inter-tube slippage and structural reformation with twist, there is an optimal twist level to achieve desired properties. Low-twist CNT yarns exhibited a lower breaking strength and elongation at rupture but higher elastic modulus compared to medium- and high-twist CNT yarns. The piezoresistive response of the CNT yarns was highest at medium twist followed by high twist levels. Twist-induced compaction in the CNT yarn increases contacts between CNT bundles, improving the mobility of charge carriers. Consequently, porosity is reduced while toughness and conductivity increase with increasing twist. It was observed that specific conductivity of the CNT yarn is not constant but increases with twist angle. The understanding of the piezoresistivity of CNT yarns with respect to twist levels could be useful in optimizing their properties as sensors and actuators.

Magnetoresistance mechanisms in carbon-nanotube yarns

Carbon nanotube (CNT) yarns are novel CNT-based materials that extend the advantages of CNT from the nanoscale to macroscale applications. Herein we have modeled the electrical properties of carbon nanotube yarn as a function of temperature and magnetic field. The conductivity was well explained by 3D Mott Variable Range Hopping (VRH) law at T < 100 K. The hopping effective dimension is reduced with increasing of magnetic field. Negative magnetoresistance (MR) was observed at different magnetic field range. A quadratic MR was found at small magnetic fields up to BD2, where a deviation occurred from the quadratic magnetic field dependence of the MR. In the intermediate magnetic field region, the negative MR shows linear magnetic field dependence up to the magnetic crossover field of BD1. It was found that physical parameters such as the localization length and the density of states at the Fermi level are temperature and magnetic field dependent. In addition, a general scaling behavior was found for the MR as a function of (B/B*)1/3, where B* is a crossover magnetic field.

Single-step process to improve the mechanical properties of carbon nanotube yarn.

Carbon nanotube (CNT) yarns exhibit low tensile strength compared to conventional high-performance carbon fibers due to the facile sliding of CNTs past one another. Electron beam (e-beam) irradiation was employed for in a single-step surface modification of CNTs to improve the mechanical properties of this material. To this end, CNT yarns were simultaneously functionalized and crosslinked using acrylic acid (AA) and acrylonitrile (AN) in an e-beam irradiation process. The chemical modification of CNT yarns was confirmed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and scanning electron microscopy (SEM). The best improvement in mechanical properties was achieved on a sample treated with an aqueous solution of AA and subsequent irradiation. CNT yarn treatment with AA enhanced the strength (444.5 ± 68.4 MPa) by more than 75% and the modulus (21.5 ± 0.6 GPa) by more than 144% as compared to untreated CNT yarn (strength 251 ± 26.5 MPa and modulus 8.8 ± 1.2 GPa).

Effect of solvent/polymer infiltration and irradiation on microstructure and tensile properties of carbon nanotube yarns

Recently carbon nanotube (CNT) yarns have been gaining importance as an approach to harvest the excellent properties of the CNTs. However, the properties of CNT yarns at this stage are well below the expected value. Investigation of the structure of CNT yarns and possible approaches to enhance the strength and modulus are reported. Scanning electron microscopy and focused ion beam imaging reveal the inherently porous structure and poor orientation, emphasizing the need to enhance packing of CNT bundles in the yarns for increased strength and modulus. Densification of CNT yarn by toluene or polystyrene increases the strength by 140 or 172 % and modulus by 79 or 218 %, respectively, as compared to that of the pristine yarn. E-beam irradiation was investigated as a means to introduce crosslinking and enhanced internanotubes bonding to increase strength and modulus. However, the irradiation resulted in generation of defects and damages to the yarn contributing to reduction in strength and modulus. Raman spectroscopy studies on the irradiated samples reveal the change in bonding characteristics resulting in poor mechanical properties. Denser packing of nanotubes and increased interaction without any damage is the key to improve the properties of CNT yarns.

Effect of polymer infiltration on structure and properties of carbon nanotube yarns

Polymer-infiltrated carbon nanotube yarns (CNTYs) were prepared to enhance the mechanical and electrical properties of CNTYs through physical interactions. This work additionally explored the role of the polymer in altering the structures of the CNTYs. The reticulate structures of the CNTYs produced through aerogel methods were infiltrated with a dilute (0.05wt%) solution of polystyrene (PS), polyacrylonitrile (PAN), or polyvinyl alcohol (PVA), and the structures were characterized. The performances of the CNTYs were closely related to the junction strength and the bundle size in the reticulate CNTYs. Among the three polymers examined, infiltration of PVA—the polymer with the poorest affinity toward CNTs—yielded the greatest improvement in the mechanical and electrical properties of the CNTY. The CNTY deformation properties at each stage of the stress–strain curves could be explained based on the effects of the polymer infiltration on the structure and properties of the CNTY. The results indicated that the specific stiffness, specific strength, toughness, and electrical conductivity are significantly influenced by the molecular-level coupling between the polymer, the CNTs, and the internal structure of the CNTY.

Chemical Method for Improving Both the Electrical Conductivity and Mechanical Properties of Carbon Nanotube Yarn via Intramolecular Cross-Dehydrogenative Coupling

Chemical post-treatment of the carbon nanotube fiber (CNTF) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl3 at room temperature. The Raman intensity ratio of the G band to the D band (IG/ID ratio) of CNT fiber increased from 2.3 to 4.6 after ICDC reaction. From the XPS measurements, the AC═C/AC-C ratio of the CNT fiber increased from 3.6 to 4.8. It is of keen interest that both the electrical conductivity and tensile strength of CNT yarn improved to 3.5 × 10(3) S/cm and 420 MPa, which is 180 and 200% higher than that of neat CNT yarn.

Effect of conducting polypyrrole on the transport properties of carbon nanotube yarn

Experiments were conducted to measure the electrical conductivity in three types of pristine and carbon nanotube-polypyrrole (CNT-PPy) composite yarns and its dependence on over a wide temperature range. The experimental results fit well with the analytical models developed. The effective energy separation between localized states of the pristine CNT yarn is larger than that for both the electrochemically and chemically prepared CNT-PPy yarns. It was found that all samples are in the critical regime in the insulator–metal transition, or close to the metallic regime at low temperature. The electrical conductivity results are in good agreement with a Three Dimensional Variable Range Hopping model at low temperatures, which provides a strong indication that electron hopping is the main means of current transfer in CNT yarns at T<100K. We found that the two shell model accurately describes the electronic properties of CNT and CNT-PPy composite yarns in the temperature range of 5–350K.

Fabrication and mechanical properties of carbon nanotube yarns spun from ultra-long multi-walled carbon nanotube arrays

Carbon nanotube (CNT) yarns have been fabricated by dry spinning from vertically aligned millimeter-long multi-walled carbon nanotube (MWCNT) arrays and their mechanical properties have been studied. By using 2-mm long CNTs and densely packing of CNT yarns we achieved a tensile strength of 1068MPa and Young’s modulus of 55GPa. Our CNT yarns have diameters of tens of micrometers being easy to handle and possessing high effective load capacity up to 0.81N. We discuss mechanical properties of CNT yarns spun from relatively thick MWCNT along with a detailed analysis of various post-spin processes and their effect on CNT yarns characteristics. Also, we point out the difference between mechanical properties of dry spun CNT yarns and conventional spun textile yarns.

Effect of gamma-irradiation on the mechanical properties of carbon nanotube yarns

Gamma-irradiation of carbon nanotube yarns in air has significantly improved the tensile strength and modulus of the yarns, presumably because of an increased interaction between the individual nanotubes. The improvement has been much greater for tightly structured yarns than for loosely structured yarns. Sonic pulse tests have also shown increased sound velocity and dynamic modulus in the carbon nanotube yarns as a result of gamma-irradiation treatment. X-ray photoelectron spectroscopic analyses on progenitor carbon nanotube forests show that gamma-irradiation treatment in air has dramatically increased the concentration of oxygen, for example as carboxyl groups, in the carbon nanotube assemblies in proportion to radiation dose, indicating that carbon nanotubes were oxidized under the ionizing effect of the gamma-irradiation. Such oxygen species are thought to contribute to the interaction between carbon nanotubes and thus to the improvement of carbon nanotube yarn mechanical properties.

Synthesis and Properties of Carbon Nanotube Yarns and Textiles

ABSTRACTThe strength of macroscopic materials made of carbon nanotubes depends on the quality of the nanotubes produced, as well as various methods of post-treatment. The average diameter and length of the nanotubes can be controlled through the various parameters of a specially designed injector system, in conjunction with the CVD furnace. Large non-woven textiles and yarns of pure nanotubes are created, and then post-processed in various ways to obtain the desired products. In this way textiles over 2 square meters, and yarns of over a half kilometer have been produced with strengths unprecedented in pure carbon nanotube materials.

Tensile and electrical properties of carbon nanotube yarns and knitted tubes in pure or composite form

Carbon Nanotubes (CNTs) have exceptionally high strength and high elastic modulus, as well as good electrical and thermal conductivity. The objective of current research is to develop new lightweight, strong, and conductive materials by using CNTs primarily in pure form. Recently, we have developed a solid-state processing method that enables the CNTs to be assembled into pure yarns and webs, avoiding the problems associated with the presence of a binder, and improving the exploitation of the inherent properties of the individual CNTs. In this paper will report on recent experience with spinning CNT yarns and the effect of twist on selected properties. We also report our results on knitted tubes, in both pure and composite form.