Thermal and electrical conductivity of array-spun multi-walled carbon nanotube yarns

The electrical resistivity of CNT yarns of diameters 10–34 μm, spun from multi-walled carbon nanotube arrays, have been determined from 2 to 300 K in magnetic fields up to 9 T. The magnetoresistance is large and negative at low temperatures. The thermal conductivity also has been determined, by parallel thermal conductance, from 5 to 300 K. The room-temperature thermal conductivity of the 10 μm yarn is (60 ± 20) W m^?1 K^?1, the highest measured result for a CNT yarn to date. The thermal and electrical conductivities both decrease with increasing yarn diameter, which is attributed to structural differences that vary with the yarn diameter.     

Electrical conductivity of chemically modified multiwalled carbon nanotube/epoxy composites

The electrical conductivity of oxidized multiwalled carbon nanotubes (MWNT)/epoxy composites is investigated with respect to the chemical treatment of the MWNT. The oxidation is carried out by refluxing the as-received MWNT in concentrated HNO₃ and H₂O₂/NH₄OH solutions, respectively, under several different treatment conditions. The oxidized MWNT are negatively charged and functionalized with carboxylic groups by both solutions. The MWNT oxidized under severe conditions are well purified, but their crystalline structures are partially damaged. It is recognized that the damage to the MWNT has considerable influence on the electrical properties of the MWNT composites, causing the electrical conductivity to be lowered at a low content of MWNT and the percolation threshold to be raised. The MWNT oxidized by the mixture of H₂O₂ and NH₄OH solution provides epoxy composites with a higher conductivity than those produced with the MWNT oxidized by nitric acid over the whole range of MWNT, independently of the oxidation conditions.     

Electrical conductivity of single walled and multiwalled carbon nanotube containing wool fibers

The main purpose of this study was producing conductive wool fabric applying carbon nanotubes. Raw and oxidized wool samples were treated with carbon nanotubes in the impregnating bath in the presence of citric acid as a crosslinking agent and sodium hypophosphite as a catalyst while sonicating them in the ultrasonic bath. Electrical resistance, washing durability, and color variation of treated samples were assessed. Through SEM images, the surface morphology of treated samples was studied confirming the surface coating through carbon nanotubes. According to the results, the electrical resistance of treated wool with carbon nanotubes reduced substantially. However, the single‐walled carbon nanotubes are more useful to increase the conductivity. In addition, the wool color changed into gray after the treatment. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrical conductivity and Joule heating of polyacrylonitrile/carbon nanotube composite fibers

Carbon nanotube (CNT) can exhibit electrical conductivity and introduce electric current into polymer. Using dry-jet-wet spin technology, polyacrylonitrile (PAN)/CNT composite fibers with 15 wt% and 20 wt% of CNT content were fabricated. The electrical conductivity of PAN/CNT fibers was enhanced by the annealing process at different temperatures and changed with time. These fibers could also respond to stretching, and the electrical conductivity decreased by 50% when the elongation reached 3%. In addition, electrical current can induce Joule heating effect and thermally transform PAN/CNT composite fibers. With the application of various electrical currents up to 7 mA at a fixed length, conductivity was enhanced from around 25 S/m to higher than 800 S/m, and composite fibers were stabilized in air. The temperature of composite fibers can increase from room temperature to several hundreds of degree Celsius measured by an infra-red (IR) microscope. Joule heating effect can also be estimated according to one-dimensional steady-state heat transfer equation, which reveals the temperature can be high enough to stabilize or carbonize fibers. As a result, this research provides a new idea of heating fabrics for thermal regulation, and a new approach for stabilizing and carbonizing PAN-based carbon fibers.     

Electrical conductivity of carbon black/single-wall carbon nanotube/low-density polyethylene ternary composite foam

In order to obtain high electrical conductive low-density polyethylene (LDPE) foam, carbon black (CB), single-wall carbon nanotube (SWCNT), and LDPE (CB/SWCNT/LDPE) ternary composite foams were successfully fabricated by chemical compression molding method. The electrical conductivity, mechanical properties, microstructure, density, and crystallinity of the foam were studied in detail. It can be found that CB and SWCNT have synergistic effect. For the CB/SWCNT/LDPE composite foam which containing 19 wt % CB and 0.05 wt % SWCNT, its density is only 0.082 g cm⁻¹ and the electrical conductivity can reach at 2.88 × 10⁻⁵ S cm⁻³, which is far more than 15 orders of magnitudes of pure polyethylene and 4 orders of magnitudes times higher than sample which CB content is 19 wt %. It is noteworthy that ultralow concentration of SWCNT could drastically improve the electrical conductivity and reduce the density of LDPE foams. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48382.     

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 1068 MPa and Young’s modulus of 55 GPa. Our CNT yarns have diameters of tens of micrometers being easy to handle and possessing high effective load capacity up to 0.81 N. 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.     

Strain dependence of electrical resistance in carbon nanotube yarns

Carbon nanotube forests or arrays can be drawn into a web and further twisted into threads. These carbon nanotube threads contain thousands of carbon nanotubes in their cross-sections and can be further composed into yarns that consist of one or more threads. The superior mechanical, thermal and electrical properties of carbon nanotubes are not translated into the carbon nanotube yarns. However, carbon nanotube yarns still exhibit relatively high mechanical stiffness and strength, and low electrical resistivity. More importantly, carbon nanotube yarns exhibit piezoimpedance that could be used for sensing purposes. In order to use carbon nanotube yarns as piezoimpedance-based sensors for structural health monitoring, it is necessary to determine the change in impedance of the yarn as a function of its mechanical strain or stress. This paper presents the results of an experimental study on the coupled mechanical response and electrical response in the direct current mode of the carbon nanotube yarn. A behavior consisting of a negative piezoresistive response was encountered during most of the deformation range of the yarn. This response was shown to exhibit a parabolic response and it was followed by a linear positive piezoresistive response that preceded the failure of the yarn.     

Electrical conductivity and electromagnetic interference shielding efficiency of carbon nanotube/cellulose composite paper

Composite material consisting of carbon nanotubes (CNTs) combined with cellulose paper has been developed. The CNTs form a continuously interconnected network on the cellulose fibers and the conditions for the mass production of the paper have been optimized. Paper containing 8.32 wt% CNTs is electrically conductive with a volume resistance of 5.3 × 10⁻¹ Ω cm. The composite paper is capable of shielding electromagnetic interference over the tested range of 15-40 GHz, particularly in range of 30-40 GHz, with absorption as the essential shielding mechanism. The paper is physically strong yet highly flexible.     

Carbon nanotube yarns

A CNT yarn is a collection of interlocked CNTs which form a long and continuous fiber of macroscopic scale. CNT yarns of more than a kilometer are now available so that they have been drawing ever-growing attention from the scientific community. In principle, CNT yarns can inherit the excellent electrical, mechanical and chemical properties of CNTs provided they are produced perfectly. In this perspective review, the production methods of CNT yarns are extensively investigated and reported in detail. Although CNT yarns have a great potential to revolutionize our future, it can only be possible by improving their essential material properties such as tensile strength and edectrical conductivity.     

A self-entanglement mechanism for continuous pulling of carbon nanotube yarns

We report an in situ electron microscopy study of pulling mechanism of super-aligned carbon nanotube (CNT) arrays grown by chemical vapor deposition. The formation of entangled structures at the ends of CNT bundles during pulling is very critical for the pulling process. By cutting the top and bottom layers of both pullable and not pullable CNT arrays, we confirm that the structures at the top or bottom surfaces of the as-grown CNT arrays are not the dominant reason to ensure the continuous pulling process. We have observed the formation of entangled structures when the pulling process approaches the bottom and top ends of the CNT arrays. These entangled structures are responsible for maintaining the continuity of pulling CNTs.     

Electrical conductivity of poly(vinyl alcohol)/carbon nanotube multilayer thin films: Influence of sodium polystyrene sulfonate mediated carbon nanotube dispersion

This investigation was aimed to enhance the dispersibility of multi-walled carbon nanotubes (MWCNT) using sodium polystyrene sulfonate (Na-PSS) polyelectrolyte. Subsequently, electrically conducting, multi-layer thin films are prepared utilizing layer by layer assembly method with poly(vinyl alcohol) as a host matrix. The highest extent of MWCNT dispersion was observed in MWCNT:Na-PSS ratio of 1:9 (wt/wt), which was estimated from UV-Vis spectroscopic analysis. Zeta potential measurements of Na-PSS modified MWCNT dispersion showed large negative potentials ranging from −52 to −64 mV in the most stable pH range of 4 to 10, suggesting the colloidal stability is due to the long-range repulsive nature of electrostatic interactions from negatively charged sulfonate groups. Complementary molecular dynamics simulations showed that adsorption of Na-PSS imparts a large negative potential to the carbon nanotube surface, which increases with an increase in Na-PSS concentration. The multi-layer thin film of (1:9) MWCNT:Na-PSS exhibited a DC electrical conductivity of 2.96 × 10² S/m.     

High conductivity electrospun carbon/graphene composite nanofiber yarns

Polyacrylonitrile/graphene (PAN/GP) composite nanofiber filaments were spun continuously by a homemade eight‐needle electrospinning device with an auxiliary electrode, and then, yarns were obtained by plying and successive twisting. Subsequently, the composite yarns were stabilized at 250–280°C for 1–2 h and then carbonized at 800–1100°C for 1–3 h. The diameter of yarns significantly decreased by over 60% after carbonization and the structure became more compact. The optimum stabilization conditions were at 270°C with holding for 1.5 h. The addition of GP at a low mass fraction (<1%) promoted the formation of ladder‐like structures and ordered graphitic structures during stabilization and carbonization. It seems there were defects in the pristine CNF, and the addition of GP reduced the defects. The conductivity of the composite CNF yarn sharply increased with the increase of GP content to 1%, and then decreased. The maximum value was 66.44 ± 13.16 S/cm at 1100°C held for 3 h. The mechanical properties for composite CNF yarns were performed. The maximum stress and modulus were 59.49 MPa and 14.63 GPa, respectively. POLYM. ENG. SCI., 58:903–912, 2018. © 2017 Society of Plastics Engineers     

Electrical conductivity of poly(vinylidene fluoride)/carbon nanotube composites with a spherical substructure

Poly(vinylidene fluoride) (PVDF)/multiwalled carbon nanotube (MWCNT) conducting composites were prepared with a percolation threshold as low as 0.07 wt%. The MWCNTs in a PVDF solution can lead to the formation of spherical PVDF/MWCNT composite particles by sonication. The MWCNTs coated on the surfaces of the spherical particles form a conduction network when the spheres coalesce to form a solid composite. The existence of the spherical particles with a substructure results in the reduction in MWCNT content and improves the electrical conductivity of the composites.     

Electrical and thermal conductivity and tensile and flexural properties of carbon nanotube/polycarbonate resins

Adding conductive carbon fillers to insulating thermoplastic polymers increases the resulting composite's electrical conductivity. Carbon nanotubes (CNTs) are very effective at increasing composite electrical conductivity at low loading levels without compromising composite tensile and flexural properties. In this study, varying amounts (2–8 wt %) of CNTs were added to polycarbonate (PC) by melt compounding, and the resulting composites were tested for electrical conductivity (1/electrical resistivity), thermal conductivity, and tensile and flexural properties. The percolation threshold was less than 1.4 vol % CNT, likely because of CNTs high aspect ratio (1000). The addition of CNT to PC increased the composite electrical and thermal conductivity and tensile and flexural modulus. The 6 wt % (4.2 vol %) CNT in PC resin had a good combination of properties for electrical conductivity applications. The electrical resistivity and thermal conductivity were 18 Ω‐cm and 0.28 W/m · K, respectively. The tensile modulus, ultimate tensile strength (UTS), and strain at UTS were 2.7 GPa, 56 MPa, and 2.8%, respectively. The flexural modulus, ultimate flexural strength, and strain at ultimate flexural strength were 3.6 GPa, 125 MPa, and 5.5%, respectively. Ductile tensile behavior is noted in pure PC and in samples containing up to 6 wt % CNT. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High performance carbon nanotube spun yarns from a crosslinked network

We report a new method to create covalent crosslinks between carbon nanotubes (CNTs) with reduced intertube and interbundle spaces, for improving the mechanical properties of CNT spun yarns. This is achieved through the pretreatment of a CNT yarn with 4-carboxybenzenediazonium tetrafluoroborate to form reactive carboxyphenyl groups on the CNT sidewalls. These carboxyphenyl groups are then reacted with a multifunctional crosslinker hexa(methoxymethyl) melamine, leading to a highly crosslinked network within the yarn. The CNT yarns were characterized by X-ray photoelectron spectroscopy, focused ion beam scanning electron microscope, and also assessed for their mechanical properties. The results showed that the method developed effectively improved mechanical properties of CNT yarns: we are able to produce CNT yarns with a tensile strength up to 2.5 GPa and Young’s modulus 121 GPa.     

Investigation of electro-mechanical behavior of carbon nanotube yarns during tensile loading

Carbon nanotube (CNT) yarns were evaluated for sensor applications by measuring electrical properties during uniaxial tension loading. Mechanical properties (tenacity and failure strain) and electrical properties (resistivity and gauge factor) were investigated and statistical distributions for these properties were obtained. Cyclic loading test results showed that permanent strain after unloading exists and that the resistance at zero load increases linearly with permanent strain. Furthermore, the relative resistance change during loading was found to be linear with strain. Although mechanical properties of CNT yarns exhibited a significant statistical variation, the resistance was found to have much less statistical variation making them good candidates as sensors for structural health monitoring in composites.     

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.     

Poisson’s ratio and porosity of carbon nanotube dry-spun yarns

The Poisson’s ratio of carbon nanotube (CNT) dry-spun yarns can be tuned over an extremely wide range of values that are up to 20-30 times higher than common solid materials. This is a result of the highly variable porosity of the yarn structure, from 90% in very low twist yarns to 40% in high twist yarns. The change of CNT geometry during the conversion from forest to web also plays an important role in the formation of CNT bundles and consequently influences the CNT dry-spun yarn structure. The CNT dry-spun yarn achieved its maximum specific strength when the CNTs on the yarn surface formed a 20° angle to the yarn axis. These CNT dry-spun yarn structure-property relationships can be utilized in the design of different applications, such as tuning the sensitivity of sensors and the functional characteristics of CNT composites.     

Electrical conductivity of vapor-grown carbon fibers

Carbon fibers grown by pyrolysis of natural gas were heat-treated at temperatures ranging from 1400 to 3000°C, and characterized by X-ray diffraction. Their electrical resistivity is reported for temperatures between 10 and 370 K, and explained for heat treatment above 2200°C using a simple graphitic band model. Filaments heat-treated at lower temperatures and as-grown fibers show a resistivity with a small temperature dependence.     

Dispersion and thermal conductivity of carbon nanotube composites

A mechanical method was used to shorten carbon nanotubes (CNTs) for improving dispersion without reducing their thermal conductivity. Single walled carbon nanotubes (SWCNTs) were mechanically cut to produce short and open-ended fullerene pipes. These shortened SWCNTs were then used in polymer composites. Both atomic force microscopy and scanning electron microscopy characterizations suggested that nanotube shortening significantly improved CNT dispersion. Thermal conductivity of composites containing short CNTs were found to be much better than those containing pristine CNTs.