Small-diameter Carbon Nanotubes Research Articles

Characterization of different size reinforcement effects on microstructural failure mechanism in carbon nanotube-reinforced aluminum composites

In this study, we investigated the effect of reinforcement sizes on the tensile strength and ductility of carbon nanotube (CNT)-reinforced aluminum matrix composites fabricated through ball milling, followed by hot extrusion of a powder encapsulated in an aluminum container. We analyzed the microstructural properties of the samples, including the aluminum grain size, its spatial variation with the alignment of CNT, and CNT length. Nanoindentation test results revealed the spatial variation of hardness and Young’s modulus of composites with small-diameter CNTs, indicating local Al4C3 formation and interlock structure resulting from dislocation accumulation during the fabrication process. This explains dimples of different sizes observed on the fracture surfaces of the samples and the occurrence of CNT pullout. Furthermore, we proposed the failure mechanism of the composites under tensile strain and calculated the failure strain using the Whitehouse–Clyne model. The calculated failure strain agrees well with the experimental values. The high ductility of the composites is attributed to the large grain fracture and rotation of neighboring grains due to the constraint imposed by CNTs.

Carbon nanotube yarn with small outer diameter to maximize the electrochemical performance of artificial muscles

Electrochemically powered carbon nanotube (CNT) artificial muscles have garnered significant attention owing to their chemical stability, low operating voltage, and impressive actuation performance. Notably, twist-based CNT artificial muscles have demonstrated superior actuation performance by maximizing untwisting motion of the CNT yarn. However, the microscopic design of CNTs is yet to be reported, although CNTs comprising CNT yarn muscles are key determinants of performance. Here, we first establish a correlation between the diameter of CNTs and the actuation performance of artificial muscles. The structural reason for the higher deformability is elucidated employing molecular dynamics simulations. The obtained computational simulation results were consistent with the experimentally fabricated yarn. Remarkably, the CNT yarn muscle composed of small-diameter CNTs exhibited a work capacity of 3.57 J/g, significantly higher than previously reported ones. Our findings provide a fundamental design range of CNT diameters that can significantly enhance the performance of electrochemically powered artificial muscles.

Fast Water Transport through Subnanometer Diameter Vertically Aligned Carbon Nanotube Membranes.

Small-diameter carbon nanotubes (CNTs) have outstanding mass-transport properties, especially enhanced water flow. Here, we report on water transport through the first macroscopic membranes with vertically oriented, subnanometer (0.8 nm) CNT pores, made by a scalable, solution-based method with electric-field alignment of bulk-grown single-wall CNTs (SWCNTs). After plasma etching to open pores, vertically aligned CNTs served as the primary pathway for liquid-water transport. The CNT membranes showed fast pressure-driven water transport, with up to 105-fold enhancement compared to no-slip Hagen-Poiseuille flow. Comparing 0.8 and 3 nm CNTs, we found that the hydrodynamic slip lengths increased with decreasing nanotube diameter, reaching 8.5 μm for the smaller-diameter CNTs. The results suggest that pressure-driven water transport in small-diameter CNTs is increasingly dominated by entrance resistance, thus becoming independent of nanotube length. Scalably fabricated membranes incorporating vertically aligned subnanometer CNT pores could have applications in water filtration, desalination, and energy harvesting.

Investigating the Electromechanical Sensitivity of Carbon-Nanotube-Coated Microfibers.

The piezoresistance of carbon nanotube (CNT)-coated microfibers is examined using diametric compression. Diverse CNT forest morphologies were studied by changing the CNT length, diameter, and areal density via synthesis time and fiber surface treatment prior to CNT synthesis. Large-diameter (30-60 nm) and relatively low-density CNTs were synthesized on as-received glass fibers. Small-diameter (5-30 nm) and-high density CNTs were synthesized on glass fibers coated with 10 nm of alumina. The CNT length was controlled by adjusting synthesis time. Electromechanical compression was performed by measuring the electrical resistance in the axial direction during diametric compression. Gauge factors exceeding three were measured for small-diameter (<25 μm) coated fibers, corresponding to as much as 35% resistance change per micrometer of compression. The gauge factor for high-density, small-diameter CNT forests was generally greater than those for low-density, large-diameter forests. A finite element simulation shows that the piezoresistive response originates from both the contact resistance and intrinsic resistance of the forest itself. The change in contact and intrinsic resistance are balanced for relatively short CNT forests, while the response is dominated by CNT electrode contact resistance for taller CNT forests. These results are expected to guide the design of piezoresistive flow and tactile sensors.

Fabrication of small-diameter carbon nanotubes using a coordination polymer with a free-oxygen ligand as a catalyst precursor

Carbon nanotubes (CNTs) that are derived from coordination polymers (CPs) and which have controllable structures have served as a significant class of sorbents in renewable materials. However, it is difficult to achieve efficient conversion of CPs to small-diameter CNTs (SDCNTs) via chemical vapor deposition (CVD). As described herein, we first report the large-scale growth of SDCNTs from a Co-based CP. The oxygen atoms of trimesic acid (BTC) which surround the Co-based CP crystals impede the aggregation of Co nanocatalysts so that they effectively serve as a unique “sieve” which allows the catalyst to promote the formation of SDCNTs during the CVD process. CNTs with a diameter of ∼14 nm evolved from the pristine CP architecture. This strategy is novel and provides a new approach for the large-scale preparation of SDCNTs, and it that may facilitate the development of high performance and inexpensive sorbents as well as photocatalysts for water treatment.

Effect of Carbon Nanotube Size on Electrical Properties of Cement Mortar under Different Temperatures and Water Content

The effects of temperature and water content on the electrical conductivity of cement mortar with different sizes of carbon nanotubes were studied, and the effect of the size of carbon nanotubes on the electrical conductivity of cement mortar was revealed. The results show that the small diameter carbon nanotubes have the best enhancement effect on the electrical conductivity of cement mortar. The electrical conductivity of cement mortar with different diameters of carbon nanotubes is positively correlated with water content, and with the decrease of the diameter of carbon nanotubes in the sample, the effect of water content on the electrical conductivity of carbon nanotube cement mortar becomes smaller and smaller. With the increase of temperature, the electrical conductivity of cement mortar containing carbon nanotubes of different diameters increases in varying degrees, but the increase of samples with small diameter carbon nanotubes is the smallest, indicating that the electrical conductivity of cement mortars with small diameter carbon nanotubes is less affected by temperature.

Моделирование механических и физических свойств пучка углеродных нанотрубок при поперечном сжатии с использованием цепной модели с редуцированным числом степеней свободы

The paper studies a bundle of oriented carbon nanotubes (CNTs) under the transverse loading under the plane deformation conditions within the framework of a molecular dynamics model with a reduced number of degrees of freedom. The model takes into account CNT wall stretching and bending, as well as van der Waals interactions. Each CNT is represented by a ring of atoms with two degrees of freedom in the plane of the ring. The discrete nature of the model allows describing the large curvature of the CNT wall and the destruction of CNTs at very high pressure. CNT crystal equilibrium structures are obtained under the strain-controlled biaxial loading. Separate CNTs of a sufficiently large diameter have two equilibrium states: with a round and collapsed cross section. Small-diameter CNTs in the free state can only have a circular cross section. The study identified the presence of two phase transitions observed during biaxial compression of a CNT bundle. The first transformation similar to phase transition of the second order leads to ellipticization of CNT cross sections. As a result of the second transition of the first order, bundled CNTs appear in the beam, the proportion of which gradually increases with the increase in compressive strain. The authors calculated beam elasticity constants such as Young’s moduli, shear modulus, and Poisson’s ratios. The study shows that one of the equilibrium structures (with elliptical CNT cross sections) has the property of a partial auxetic, that is, it has a negative Poisson’s ratio under uniaxial loading in a certain direction. The proposed chain model can be effectively applied to analyze physical and mechanical properties of bundles of single-walled or multi-walled CNTs under the plane deformation conditions, and after simple modifications, it can be used to similar structures made of other two-dimensional nanomaterials.

Development of wireless SHM sensor node for in-flight real-time monitoring using embedded CNT fiber sensors

Structural health monitoring (SHM) is essential for composite unmanned aerial vehicles (UAVs). Additionally, because UAVs are extremely sensitive to weight and volume, the minimal addition of weight and volume by the SHM system is crucial. Therefore, we proposed a compact and lightweight wireless SHM sensor node and an embedded carbon nanotube (CNT) fiber sensor for in-flight SHM of UAVs. The wireless SHM sensor node was composed of an analog sensing circuit, wireless microcontroller unit, and analog low pass filter. The small diameter CNT fiber sensor was developed to be easily embedded inside composite structures and to enhance their structural properties while performing as an SHM sensor. Glass composite skin with embedded CNT fiber sensors composed of ultra-high-molecular-weight polyethylene, polyurethane, CNT, and carbon black were installed in the aircraft. For comparison, a strain gauge attached at the center of a long CNT fiber sensor was also used during in-flight measurement. In-flight strain measurements from both the CNT fiber sensor and the strain gauge were continuously transmitted to the ground station and were compared with the flight data. Furthermore, an impact tester was installed inside the wing to simulate impact during flight, and in-flight impact measurements by the CNT fiber sensor were demonstrated.

Water-ion permselectivity of narrow-diameter carbon nanotubes

Carbon nanotube (CNT) pores, which mimic the structure of the aquaporin channels, support extremely high water transport rates that make them strong candidates for building artificial water channels and high-performance membranes. Here, we measure water and ion permeation through 0.8-nm-diameter CNT porins (CNTPs)-short CNT segments embedded in lipid membranes-under optimized experimental conditions. Measured activation energy of water transport through the CNTPs agrees with the barrier values typical for single-file water transport. Well-tempered metadynamics simulations of water transport in CNTPs also report similar activation energy values and provide molecular-scale details of the mechanism for water entry into these channels. CNTPs strongly reject chloride ions and show water-salt permselectivity values comparable to those of commercial desalination membranes.

Highly efficient thermo-electrochemical energy harvesting from graphene–carbon nanotube ‘hybrid’ aerogels

Three-dimensional scaffold assemblies consisting of thermally reduced graphene oxide nanosheets and small-diameter carbon nanotubes were synthesized as potential ‘all carbon’ thermo-electrochemical energy harvesters. The facile hydrothermal–solvothermal synthesis route in which organic wet chemistry used was to inter crosslink the well-dispersed graphene oxide nanosheets with carbon nanotubes followed by freeze-drying to produce monolithic aerogel networks with ultralow densities, tunable mesoscopic pore sizes, tailorable functionality and morphology. They exhibited high electrical conductivity due to multiplex topologies owing to the integration with carbon nanotubes, which has high density of states at van Hove singularities, accompanied by expected larger surface area and sufficient edge plane sites, which in-turn enhance surface adsorption and rapid ion transportation. We conducted thermoelectric and thermo-electrochemical power generation from these ‘hybrid’ aerogel materials and using two different designs of galvanic thermo-cells. Consequently, higher Seebeck (electronic; Se as well as ionic; Sion) coefficients and thermopower generation was measured that confirmed low thermal responsiveness attributed to smaller domain size generated by hierarchical mesoporosity and open network. These multiple features demonstrate significant potential of these novel electrodes in galvanic thermocells for low-grade thermal energy harvester with higher relative conversion efficiency.

Laboratory evaluation of a personal aethalometer for assessing airborne carbon nanotube exposures

Aethalometers are direct-reading instruments primarily used for measuring black carbon (BC) concentrations in workplace and ambient atmospheres. Aethalometer BC measurements of carbon nanotubes (CNTs) were compared to measurements made by other methods when subjected to high (>30 µg/m3) and low (1–30 µg/m3) CNT aerosol concentrations representing worst-case and typical workplace concentrations, respectively. A laboratory-based system was developed to generate carbon black, as an example of a nearly pure carbon, micron-sized aerosol, and two forms of multi-walled carbon nanotubes (CNTs): small-diameter (<8 nm) and large-diameter (50–80 nm). High-concentration trials were conducted during which a scanning mobility particle sizer (SMPS) was used to track particle count concentrations over time. Relative to the behavior of the SMPS counts over time, aethalometer readings exhibited a downward drift, which is indicative of aethalometer response subjected to high BC loading on the receiving filter of the instrument. A post-sample mathematical method was applied that adequately corrected for the drift. Low-concentration trials, during which concentration drift did not occur, were conducted to test aethalometer accuracy. The average BC concentration during a trial was compared to elemental carbon (EC) concentration sampled with a quartz-fiber filter and quantified by NIOSH Method 5040. The CB and large-diameter CNT concentrations measured with the aethalometer produced slopes when regressed on EC that were not significantly different from unity, whereas the small-diameter CNTs were under-sampled by the aethalometer relative to EC. These results indicate that aethalometer response may drift when evaluating CNT exposure scenarios, such as cleaning and powder handling, that produce concentrations >30 µg/m3. However, aethalometer accuracy remains consistent over time when sampling general work zones in which CNT concentrations are expected to be <30 µg/m3. A calibration check of aethalometer response relative to EC measured with Method 5040 is recommended to ensure that the aethalometer readings are not under sampling CNT concentrations as occurred with one of the CNTs evaluated in this study.

Towards the development of nanosprings from confined carbyne chains

Abstract The synthesis of long and stable carbyne chains inside carbon nanotubes (CNTs) have recently drawn renewed attention to this linear one-dimensional carbon allotrope. Carbyne's mechanical properties are predicted to exceed that of CNTs and graphene, making it a very suitable structural component for many nanoscale applications. While carbyne's mechanical behavior under tensile loading is excellent, this carbon chain readily buckles under compressive loading. Taking this effect into account, here we study the compressive behavior of carbyne chains under the bracing effect of confinement in small diameter CNTs such as (5,5) and (6,6) and the formation of helix-shaped springs of carbyne under compressive loading in larger diameter CNTs such as (7,7) and (8,8), using molecular dynamics simulations (MD). The Young's modulus of confined carbyne chains under compression was estimated in average to be 4029 GPa when confined in (5,5) CNT and 3858 GPa when confined in (6,6) CNT, showing slight increases with chain length. We found that for looser confinements carbyne chains can buckle into a coiled helix-shaped spring with properties that depend on confinement radius and chain length. The behavior of these nanosprings follows Hooke's law and may be envisaged for applications in nanodevices .

Mechanical properties of carbon-nanotube-reinforced cementitious materials: database and statistical analysis

This paper aims to provide guidelines for selecting the correct type of carbon nanotube (CNT) to improve the mechanical properties of cementitious materials. Previous researchers have discussed the effect of CNT characteristics on their dispersion quality. However, the effect of these characteristics on the mechanical properties of CNT-reinforced cementitious materials is not fully understood. To clarify this, the study reported in this paper was conducted in two phases. In the first phase, a database was established from the literature to study the influences of three different parameters associated with CNTs (length, diameter and concentration based on the weight percent of cement powder (c-wt%)) on compressive and flexural strengths. The analyses revealed that short and small-diameter CNTs could be beneficial for increasing compressive strength. Conversely, relatively long and large-diameter CNTs were more effective in increasing flexural strength. In general, an average CNT length of 10–20 μm and an average diameter of 20–32·5 nm resulted in the highest overall mechanical performance. The optimal upper limit concentrations for flexural and compressive strengths were found to be 0·15 and 0·20 c-wt%, respectively. In the second phase of this study, the statistical analyses were experimentally verified using the CNT optimum length, two diameters and three levels of concentrations.

Strain and screening: Optical properties of a small-diameter carbon nanotube from first principles

Carbon nanotubes (CNTs) are a one-dimensional material system with intriguing physical properties that lead to emerging applications. While CNTs are unusually strain resistant compared to bulk materials, their optical-absorption spectrum is highly strain dependent. It is an open question, as to what extent this is attributed to strain-dependent (i) electronic single-particle transitions, (ii) dielectric screening, or (iii) atomic geometries including CNT radii. We use cutting-edge theoretical spectroscopy to explain strain-dependent electronic structure and optical properties of an (8,0) CNT. Quasiparticle effects are taken into account using Hedin's GW approximation and excitonic effects are described by solving a Bethe-Salpeter-equation for the optical polarization function. This accurate first-principles approach allows us to identify an inuence of strain on screening of the Coulomb electron-electron interaction and to quantify the impact on electronic structure and optical absorption of one-dimensional systems. We interpret our thoroughly converged results using an existing scaling relation and extend the use of this relation to strained CNTs: We show that it captures optical absorption with satisfactory accuracy, as long as screening, quasiparticle gap, and effective electron and hole masses of the strained CNT are known.

Morphological Phase Diagram of Gadolinium Iodide Encapsulated in Carbon Nanotubes

The melt phase encapsulation of gadolinium iodide (GdI3) in small internal diameter carbon nanotubes (CNTs) was explored to understand how the tubular structure of the host could chemically stabilize a hygroscopic metal halide. However, given the distribution of diameters in the as-received CNTs, the final sample consisted of mixed encapsulation products. These varied from the monoelemental iodine chain to the atomic layer deposition of the binary halide. Supported by density functional theory calculations, these observations led to the proposition of a morphological phase diagram for GdI3 encapsulation in CNTs as a function of the host’s internal diameter.

Future Dielectric Materials for CNT Interconnects - Possibilities and Challenges

Carbon nanotube (CNT) interconnects are emerging as the ultimate choice for next generation ultra large scale integrated (ULSI) circuits. Significant progress in precise growth of aligned CNTs and integration of multiwalled CNT interconnects into a test chip make them promising candidates for future nanoelectronic chips. Tremendous research efforts were made on silicon based ultra-low-k dielectrics for Cu interconnects, but, the most recent advancements in polymer based composites as dielectric materials open up fresh challenges in the use of low-k dielectrics for CNT interconnects. This paper reviews the emerging polymer composites like Boron Nitride Nanotubes, Graphene/Polyimide composites, Metal Organic Frameworks and small diameter CNTs. Many reviews are already exists on the synthesis, fabrication, dielectric, mechanical, chemical and thermal properties of these materials. In this review, we have explained the specific properties of these materials and the necessities for integrating them into CNT interconnects to meet the requirements of future IC designers.Keywords: low-k dielectric materials, ultra low-k dielectrics, carbon nanotubes, interconnects, dielectric constant,

Toward Small-Diameter Carbon Nanotubes Synthesized from Captured Carbon Dioxide: Critical Role of Catalyst Coarsening.

Small-diameter carbon nanotubes (CNTs) often require increased sophistication and control in synthesis processes, but exhibit improved physical properties and greater economic value over their larger-diameter counterparts. Here, we study mechanisms controlling the electrochemical synthesis of CNTs from the capture and conversion of ambient CO2 in molten salts and leverage this understanding to achieve the smallest-diameter CNTs ever reported in the literature from sustainable electrochemical synthesis routes, including some few-walled CNTs. Here, Fe catalyst layers are deposited at different thicknesses onto stainless steel to produce cathodes, and atomic layer deposition of Al2O3 is performed on Ni to produce a corrosion-resistant anode. Our findings indicate a correlation between the CNT diameter and Fe metal layer thickness following electrochemical catalyst reduction at the cathode-molten salt interface. Further, catalyst coarsening during long duration synthesis experiments leads to a 2× increase in average diameters from 3 to 60 min durations, with CNTs produced after 3 min exhibiting a tight diameter distribution centered near ∼10 nm. Energy consumption analysis for the conversion of CO2 into CNTs demonstrates energy input costs much lower than the value of CNTs-a concept that strictly requires and motivates small-diameter CNTs-and is more favorable compared to other costly CO2 conversion techniques that produce lower-value materials and products.

Morphological control of three-dimensional carbon nanotube anode for high-capacity lithium-ion battery

In this paper, we report the results of modulating the processing conditions (mainly, temperature) of a two-step method consisting of sputtering deposition of a Ni catalytic layer and chemical vapor deposition (CVD) of carbon nanotubes (CNTs) on a three-dimensional (3D)-structured Cu mesh to control the morphology of CNTs for advanced Li-ion battery (LIB) applications. We disclosed that CNT growth at a low temperature (700 °C) produced small-diameter CNTs (CNT_S) with an average diameter of ∼20 nm, while that at a high temperature (750 °C) produced large-diameter CNTs (CNT_L) with an average diameter of 200–300 nm. The high-resolution transmission electron microscopy (HR-TEM) and Raman analyses manifested poorly crystalline CNTs for both samples. CNT_S showed a specific capacity of 476 mAh g−1, which is ∼176% superior to that of CNT_L (271 mAh g−1) and ∼128% higher than the theoretical capacity of the state-of-the-art graphites and recently reported nanostructured carbon-based anode materials.

Molecular Dynamics Simulation of Carbon Structures Inside Small Diameter Carbon Nanotubes

Motivated by recent experimental results of hydrocarbon formation in small diameter carbon nanotubes filled with ferrocene molecules, we present molecular dynamics simulations with a DFT‐adjusted tight‐binding method. We increase the number of carbon atoms from 60 to 150 by inserting carbon pentagon rings into a (14,0) nanotube. We find that the structures formed during the simulation depend on the temperature as well as on the density of the carbon atoms. At lower temperatures we obtain graphene ribbons, and at higher temperatures fullerenes or nanotubes are formed. For large enough density of the carbon atoms, the formation of nanotube like structure is preferred at both low and high temperatures.

Taguchi analysis of parameters for small-diameter single wall carbon nanotube growth

Small diameter single wall carbon nanotubes are desirable for various physical and electrical properties of carbon nanotubes. Here, we report the sensitivities of parameters and the optimal conditions for small diameter carbon nanotube growth by chemical vapor deposition (CVD). These results were obtained using the Taguchi method, which is commonly used to find the optimal parameters of various processes. The possible parameter ranges given by the experimental equipment and laboratory conditions, we attempted several times to determine the proper ranges, using photoluminescence (PL) imaging to determine the exact positions of suspended carbon nanotubes on the quartz substrates after synthesis. The diameters of the carbon nanotubes were then determined from the radial breathing modes (RBM) using Raman spectroscopy with a 785nm wavelength laser. Among the 4 major parameters listed above, we concluded that the temperature was the most significant parameter in determining carbon nanotube diameter, hydrogen flow rate was the second most significant, the ethanol and argon gas flow rate was the third, and finally time was the least significant factor.