Single-walled Carbon Nanotube Bundles Research Articles

(Invited) Engineering Single Wall Carbon Nanotubes for Sub-Cellular Drug Delivery

Single wall carbon nanotubes (SWCNTs) have been rigorously studied and engineered for a myriad of applications including drug delivery due to their unique, desirable properties. Since SWCNTs bundle in aqueous media and the bundling substantially diminishes their desirable properties along with inducing cytotoxicity, strategies to disperse individually SWCNTs with therapeutic molecules and biologic excipients have been heavily investigated. However, a handful of studies has been performed to understand the interactions between therapeutic molecules and excipients with SWCNT interface as well as the mechanism of intracellular release for therapeutic effects. Additionally, little attention has been paid to how cell type and cell metabolic activity level influence internalization of SWCNTs with different lengths. In this talk, I will discuss cell type, cell metabolic activity, and SWCNT length dependent cellular processing of SWCNTs dispersed with diverse biocompatible dispersing agents. Our results demonstrate that proper choice of dispersing agent can allow for interaction with F-actin, accumulation in the endoplasmic reticulum for eventual expulsion, or accumulation in cell nucleus. Further, macrophages with relatively high cell metabolic activity level compared to other cell types such as fibroblasts have shown to internalize significantly higher amount of SWCNTs per cell. The total mass of SWCNTs internalized per cell increases with a decrease in SWCNT length. Lastly, I will discuss our recent effort to create a ternary complex of SWCNTs, drug, and protein for intracellular delivery and release of model drugs. To overcome the limitation of the existing methods being only plausible for model drugs that are soluble in aqueous solutions, we developed a facile schema to assemble stepwise various combinations of therapeutic molecules and excipients on SWCNTs in different solvents using a preformed SWCNT network. These ternary complexes allow dialing in delivery of therapeutic molecules and excipients to achieve desired cell viability reduction. These findings allow for the development of new SWCNT-based biological applications as they establish important parameters of biomolecule adsorption on SWCNTs, SWCNT internalization and subcellular processing, which are crucial for applications ranging from drug delivery to cell type-specific modulation.

Effect of Liquid-Phase Oxidative Treatments on the Purity, Hydrophilicity, and Structure of Single-Wall Carbon Nanotubes and on the Electrical Conductivity of Their Arrays

A study using a set of physicochemical methods has shown that treatment of single-wall carbon nanotubes synthesized by the electric arc method with an aqueous solution of hydrogen peroxide (followed by treatment with hydrochloric acid) and with a mixture of concentrated nitric and sulfuric acids leads to a decrease in the content of inorganic impurities in the bulk of the finished materials. The acid oxidizing mixture shows the highest performance in the process, causing splitting of the bundles of single-wall carbon nanotubes into separate nanotubes and formation of stable concentrated suspensions of the nanotubes in water and in an isopropanol–water mixture. Both kinds of liquid-phase oxidative treatment enhance the electrical conductivity of the nanotube arrays and exert no pronounced selective effect on single-walled carbon nanotubes depending on the electronic conductivity of molecules of this material.

Stretchable conductors made of single wall carbon nanotubes self-grafted on polymer films

Aiming at the accomplishment of stretchable and elastic conductive devices, we report in this work electrical, mechanical and thermal characterization of a composite conductive material obtained by self-grafting of single wall carbon nanotubes bundles on different polymeric films. The dependence of resistance of micrometric composite conductors on the applied strain was measured; the current breakdown threshold was also measured together with the corresponding temperature increase. Finally, the dependence of an AC signal attenuation for a bi-layer single wall carbon nanotubes conductor sandwiching a 25 μm thick poly-ethylene film was obtained as a function of the signal frequency, and the experimental results were satisfactorily compared to a simple RLC model.

Light-Induced Sulfur Transport inside Single-Walled Carbon Nanotubes.

Filling of single-walled carbon nanotubes (SWCNTs) and extraction of the encapsulated species from their cavities are perspective treatments for tuning the functional properties of SWCNT-based materials. Here, we have investigated sulfur-modified SWCNTs synthesized by the ampoule method. The morphology and chemical states of carbon and sulfur were analyzed by transmission electron microscopy, Raman scattering, thermogravimetric analysis, X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopies. Successful encapsulation of sulfur inside SWCNTs cavities was demonstrated. The peculiarities of interactions of SWCNTs with encapsulated and external sulfur species were analyzed in details. In particular, the donor–acceptor interaction between encapsulated sulfur and host SWCNT is experimentally demonstrated. The sulfur-filled SWCNTs were continuously irradiated in situ with polychromatic photon beam of high intensity. Comparison of X-ray spectra of the samples before and after the treatment revealed sulfur transport from the interior to the surface of SWCNTs bundles, in particular extraction of sulfur from the SWCNT cavity. These results show that the moderate heating of filled nanotubes could be used to de-encapsulate the guest species tuning the local composition, and hence, the functional properties of SWCNT-based materials.

Effect of purification on the electrical properties of transparent conductive films fabricated from single-walled carbon nanotubes

Transparent conductive films (TCFs) made of single-walled carbon nanotubes (SWCNTs) are usually fabricated using highly pure SWCNTs. Obtaining pure SWCNTs is an important step for harnessing their excellent electrical properties. Herein, we studied the effect of purification of SWCNTs by thermal and acid processes on the electrical properties of TCFs. These purification processes also affected the length and diameter of the SWCNT bundles. The purity of SWCNTs was determined by UV–visible-near-infrared spectroscopy and the metal content by thermogravimetric analysis. TCFs were made by spraying aqueous suspensions of SWCNTs having different purities onto polyethylene terephthalate substrates, and the ratios of dc to optical conductivities of the films were compared. Thermally purified (TP) SWCNT TCFs had a higher ratio than thermally and acid-purified (TAP) ones even though the purity of the TP-SWCNTs was lower than that of the TAP-SWCNTs. The conducting paths of the SWCNT bundle networks in the TP-SWCNT TCFs were well organized, because nanosized graphitic nanoparticles and metal catalysts occupied the spaces between the CNT bundles or networks without hindering the network connections. Although the SWCNT purity affected the conductivity of the SWCNT TCFs, the network property of lower junction resistance with smaller bundle diameter was more influential on film conductivity.

Anharmonic Effects in Single-Walled Carbon Nanotubes Analyzed through Low-Temperature Raman Imaging

The high thermal conductivity of single-walled carbon nanotubes (SWCNTs) has gained much attention for their applications in potential thermal devices. Here, we investigate anharmonic effects, originated from phonon interactions, of SWCNT bundles by temperature dependent Raman imaging using our home-built mini cryostat system. The cryostat system is small enough to be mounted on a piezo scanner that suppresses thermal drift, enabling Raman imaging at different temperatures. We obtained Raman spectral images of several SWCNT bundles with a spatial resolution of a few hundred nanometers at different temperatures. We found that different bundles show different temperature dependences of Raman peak intensity, shift, and width. The temperature dependence was further elucidated by considering the sample topography observed by atomic force microscopy, where bundle effects seem to play an important role to influence the anharmonicity. The temperature-dependent Raman analysis based on spatially resolved imaging will be a powerful tool to investigate anharmonic effects of advanced carbon nanomaterials as well as to realize in situ visualization of thermal properties for future thermal devices.

Thermal conductivity reduction in carbon nanotube by fullerene encapsulation: A molecular dynamics study

Single-walled carbon nanotubes (SWCNTs) in their pristine form have high thermal conductivity whose further improvement has attracted a lot of interest. Some theoretical studies have suggested that the thermal conductivity of a (10,10) SWCNT is dramatically enhanced by C60 fullerene encapsulation. However, recent experiments on SWCNT bundles show that fullerene encapsulation leads to a reduction rather than an increase in thermal conductivity. Here, we employ three different molecular dynamics methods to study the influence of C60 encapsulation on heat transport in a (10,10) SWCNT. All the three methods consistently predict a reduction of the thermal conductivity of (10,10) SWCNT upon C60 encapsulation by 20%−30%, in agreement with experimental results on bundles of SWCNTs. We demonstrate that there is a simulation artifact in the Green-Kubo method which gives anomalously large thermal conductivity from artificial convection. Our results show that the C60 molecules conduct little heat compared to the outer SWCNT and reduce the phonon mean free paths of the SWCNT by inducing extra phonon scattering. We also find that the thermal conductivity of a (10,10) SWCNT monotonically decreases with increasing filling ratio of C60 molecules.

Polymer additive-combusted thermoelectric buckypapers for three-dimensional stacked paper thermoelectric generator

The use of polymer additives is effective for the fabrication of homogeneous single-walled carbon nanotube (SWCNT) films. However, the polymer chains located on the surface of SWCNT bundles act as barriers for electrical transport between SWCNTs and the chemical doping of SWCNTs. In this study, the combustion process of freestanding SWCNT/polymer films for the effective removal of the polymer additive and thermoelectric applications were investigated. By introducing the combustion process, high-performance p-type and n-type thermoelectric buckypapers were fabricated. The combusted and FeCl3-doped buckypapers with excellent electrical conductivity can be used as electrode materials in thermoelectric generators. Furthermore, a paper-based thermoelectric generator three-dimensional stacked for efficient energy harvesting using the vertical temperature difference was demonstrated. The thermoelectric generator with a thermal contact area of 1.2cm2 exhibited a maximum output power of 2.48μW with a vertical temperature difference of 30K.

High-performance transparent conducting films of long single-walled carbon nanotubes synthesized from toluene alone

Single-walled carbon nanotube (SWCNT) transparent conducting films (TCFs) are attracting increasing attention due to their exceptional optoelectronic properties. Toluene is a proposed carbon source for SWCNT synthesis, but the growth parameters of SWCNTs and their TCF optoelectronic performance (i.e., sheet resistance versus transmittance) have been insufficiently evaluated. Here, we have for the first time reported a systematic study of the fabrication of high-performance SWCNT TCFs using toluene alone as the carbon source. The mechanisms behind each observed phenomenon were elucidated using optical and microscopy techniques. By optimizing the growth parameters, high yields of SWCNT TCFs exhibiting a considerably low sheet resistance of 57 Ω/sq at 90% transmittance were obtained. This competitive optoelectronic performance is mainly attributable to long SWCNT bundles (mean length is 41.4 μm) in the film. Additionally, a chirality map determined by electron diffraction displays a bimodal distribution of chiral angles divided at 15°, which is close to both armchair and zigzag edges. Our study paved the way towards scaled-up production of SWCNTs for the fabrication of high-performance TCFs for industrial applications.

Preparation and transport properties of oriented buckypapers with single walled carbon nanotubes

Buckypapers (BP) with carbon nanotubes (CNT) are very promising for a lot of applications, in which their high conductance, strength and small weight are required. In this work, isotropic BP were prepared using the solution-based deposition that includes the single walled carbon nanotubes (SWCNT) dispersion and the dispersion filtration from a solvent. To increase the BP conductivity, the orientation of the SWCNT bundles composing BP and a following iodine doping were applied. The method of extrusion through the narrow (300 µm) gap was used for the SWCNT orientation. The temperature dependences of conductance for isotropic, oriented and doped BP were studied to understand the effect of CNT alignment and the mechanism of transport through SWCNT BP. It was shown that bundle orientation increases the BP conductivity from ~10 3 S × cm -1 to ~10 4 S × cm -1 , and iodine doping of oriented samples additionally increase the conductivity by an order. The fluctuation – assisted tunneling between CNT bundles was used to describe the mechanism of low temperature conductivity.

Formation of single-walled carbon nanotube-ruthenium nanoparticles in ethanol upon microwave radiation

In this work, an environmentally friendly microwave method was employed to rapidly synthesize a single-walled carbon nanotube-Ru nanoparticle (SWCNT-Ru) catalyst utilizing ethanol as the reducing agent. In general, the SWCNT-Ru nanoparticle catalyst facilitated the degradation of Congo red dye solutions, of both low and high concentrations, within eight minutes at room temperature, and possessed great recoverability and reusability properties. High-resolution transmission electron microscopy (HR-TEM) analysis of the SWCNT-Ru nanoparticle catalyst, which was synthesized with 0.05 wt% RuCl3 in ethanol, revealed highly dispersed Ru nanoparticles of the averaged size of 2.0 nm ± 0.5 nm onto the single-walled carbon nanotube bundles. Raman spectroscopy analysis indicated that there was no alteration to the nanotube structural framework upon the formation of the Ru nanoparticles. UV–Visible spectroscopy analysis indicated that the electronic properties of both smaller and larger diameters of SWCNTs were altered upon the coordination of the Ru nanoparticles. In addition, studies showed that when using ethanol as a reducing agent, concentrations of the RuCl3 salt must remain below 0.10 wt% to facilitate the production of Ru nanoparticles with efficient catalytic properties.

Temperature dependence of the Seebeck coefficient for mixed semiconducting and metallic single-wall carbon nanotube bundles

The temperature (T) dependence of the Seebeck coefficient (S) for single-wall carbon nanotube (SWCNT) bundles was systematically investigated as a function of the chemical potential (μ) through theoretical simulations employing non-equilibrium Green’s function theory. The bundles were modeled as laterally aligned parallel circuits of semiconducting and metallic SWCNTs. The T dependence of S varied substantially with μ and with metallic SWCNT content. The calculated results semi-quantitatively reproduced the typical behavior observed experimentally for SWCNT films with chemical doping reported previously.

Low temperature charge transport in arrays of single-walled carbon nanotube bundles with radiation induced defects

Low temperature charge transport in arrays of single-walled carbon nanotube bundles with radiation induced defects

Freestanding bilayers of drop-cast single-walled carbon nanotubes and electropolymerized poly(3,4-ethylenedioxythiophene) for thermoelectric energy harvesting

Abstract Poly(3,4-ethylenedioxythiophene) (PEDOT) and single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials that exhibit flexibility and high performance. To realize improved structural and thermoelectric properties, we fabricated PEDOT/SWCNT bilayers consisting of drop-cast SWCNTs and electropolymerized PEDOT. We prepared two types of PEDOT layers using electrolyte solvents of water/methanol (Sample A) and acetonitrile (Sample B). Sample B achieved a flexible freestanding state, whereas Sample A was broken with part of the sample remaining on the substrate. Scanning electron microscopy revealed that the PEDOT layer in Sample A filled the gaps between the SWCNT bundles. The PEDOT layer in Sample B consisted of chain-like structures that mostly covered the surface of the SWCNT layer, which were speculated to increase the strength of the freestanding state. The structural properties of the bilayers were examined using Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Although slight structural differences were observed between Samples A and B, both samples exhibited the characteristics of PEDOT and SWCNTs. Measurement of the thermoelectric properties near 300 K afforded power factors of 12.5 and 13.9 μW/(m·K2) for Samples A and B, respectively. Therefore, we demonstrated the successful fabrication of freestanding PEDOT/SWCNT bilayers (Sample B) with relatively high thermoelectric performance.

Crystal phase control synthesis of metallic 1T-WS2 nanosheets incorporating single walled carbon nanotubes to construct superior microwave absorber

Two-dimensional transition metal dichalcogenides (TMDs) have attracted tremendous attentions due to their unique properties, and the development of phase control technique brings out new opportunities in emerging application fields. In this work, tungsten disulfide (WS2) nanosheets containing 1T phase predominately were incorporated with single walled carbon nanotubes (SWCNTs) through a facial hydrothermal method. Two-dimensional flexible and ultrathin WS2 nanosheets were in-situ grown on one-dimensional SWCNTs bundles, further forming typical urchin-like microsphere with diameters distributing in the range of 2–3 μm uniformly. Accordingly, dielectric loss could be significantly enhanced due to the strong interface coupling effect between WS2 nanosheets and SWCNTs bundles, which induced considerable electrical conductivity and abundant capacitor-like structures. Consequently, the minimum reflection loss (RL) could reach up to −66 dB at 8.3 GHz with a matching thickness of 2.2 mm. Furthermore, RL values lower than −10 dB could be attained in the range of 3.0–18.0 GHz with integrated thicknesses from 5.0 to 1.0 mm. Prospectively, our present work may provide new opportunity to design TMDs based composites by means of crystal phase control technique as lightweight and high-performance microwave absorbers.

Solution-Processed Carbon Nanotube Buckypapers for Foldable Thermoelectric Generators.

Freestanding single-walled carbon nanotube (SWCNT) buckypapers with thicknesses of ∼30 μm are fabricated using a simple bar-coating process. The Seebeck coefficient and electrical conductivity of the SWCNT buckypapers are affected by the composition of the dispersion solvent mixture. The maximum p-type power factor of a SWCNT buckypaper is 411 ± 13 μW m-1 K-2. The inverse relationship between the Seebeck coefficient and electrical conductivity of the SWCNT buckypapers may be explained by the number density of junctions between the SWCNT bundles. Using the SWCNT buckypapers, which can be cut, folded, and pasted, a foldable thermoelectric generator is fabricated. The thermoelectric generator folded to an area of 2.25 cm2 exhibits a maximum power of 10.3 μW at a vertical temperature difference of 30 K.

Fabrication of high-strength carbon nanotube bundles using iron oxides co-assisted chemical vapor deposition

We report the fabrication of centimeter-long, defect-free, and parallel-aligned single-wall carbon nanotubes (SWCNTs) using a laboratory-designed two-step catalytic chemical vapor deposition method. Our in situ mass spectral analysis reveals that the initial stainless-derived iron oxide block decomposes methane into acetylene and ethylene, subsequently promoting the growth of high-purity SWCNTs on the second pigment-derived iron oxide fine powders dispersed on the Si/SiO2 substrate. Raman spectral imaging shows the negligible defect-induced D-band in the resulting sample, indicating the highly crystalline structure of SWCNTs. By using a gas-flow-type mechanical test system, an SWCNT bundle containing 20 components of individual SWCNTs exhibits the tensile strength over 50 GPa. Since the catalysts used in this study are widely available on the industrial scale, our iron oxide coassisted method will lead to the scalable production of high-strength SWCNT bundles.

Heat Capacity of an Ordered Bundle of Single-Walled Carbon Nanotubes

A quantum-statistical model of the thermodynamic properties of an ordered bundle of the single-walled carbon nanotubes is proposed. Generalization of the Debye heat capacity theory for the d dimensional phonon continuum is used to calculate the heat capacity. A formula for isochoric heat capacity is obtained; it contains two characteristic temperatures related to the macro- and the microstructural vibrational contributions. The calculations are in good agreement with the experimental data.

Thermoelectric properties of single-wall carbon nanotube networks

The Seebeck coefficient S and power factor P of single-wall carbon nanotube (SWCNT) networks were systematically investigated as a function of chemical potential μ, based on theoretical simulations employing non-equilibrium Green’s function theory. The results focused on the gap regions of semiconducting (s-)SWCNTs. The thermoelectric properties of individual SWCNTs were classified into three groups: s-SWCNTs, metallic (m-)SWCNTs, and pseudo-metallic SWCNTs. The maximum values of P for individual s-SWCNTs was independent of SWCNT diameter. In parallel and serial networks of SWCNTs, S and P were found to be very sensitive to the amount of m-SWCNTs, as well as the SWCNT diameter distributions. A comparison with experimental results suggested that an SWCNT bundle can be modeled as a “rope” with an equivalent S calculated for parallel circuits. The presence of SWCNT junctions in the films substantially reduced the P value from those of the composing SWCNTs while S was almost unvaried.

Antioxidative Lithium Reservoir Based on Interstitial Channels of Carbon Nanotube Bundles.

Lithium (Li) metal has garnered considerable attention in next-generation battery anodes. However, its environmental vulnerability, along with the electrochemical instability and safety failures, poses a formidable challenge to commercial use. Here, we describe a new class of antioxidative Li reservoir based on interstitial channels of single-walled carbon nanotube (SWCNT) bundles. The Li preferentially confined in the interstitial channels exhibits unusual thermodynamic stability and exceptional capacity even after exposure to harsh environmental conditions, thereby enabling us to propose a new lithiation/delithiation mechanism in carbon nanotubes. To explore practical application of this approach, the Li confined in the SWCNT bundles is electrochemically extracted and subsequently plated on a copper foil. The resulting Li-plated copper foil shows reliable charge/discharge behavior comparable to those of pristine Li foils. Benefiting from the confinement effect of the interstitial channels, the SWCNT bundles hold great promise as an environmentally tolerant, high-capacity Li reservoir.