Diameter‐ and Metallicity‐Selective Enrichment of Single‐Walled Carbon Nanotubes Using Polymethacrylates with Pendant Aromatic Functional Groups

Current methods for the synthesis of single‐walled nanotubes (SWNTs) produce mixtures of semiconducting (sem‐) and metallic (met‐) nanotubes. Most approaches to the chemical separation of sem‐/met‐SWNTs are based on small neutral molecules or conjugated aromatic polymers, which characteristically have low separation/dispersion efficiencies or present difficulties in the postseparation removal of the polymer so that the resulting field‐effect transistors (FETs) have poor performance. In this Full Paper, the use of three polymethacrylates with different pendant aromatic functional groups to separate cobalt–molybdenum catalyst (CoMoCAT) SWNTs according to their metallicity and diameters is reported. UV/Vis/NIR spectroscopy indicates that poly(methyl‐methacrylate‐co‐fluorescein‐o‐acrylate) (PMMAFA) and poly(9‐anthracenylmethyl‐methacrylate) (PAMMA) preferentially disperse semiconducting SWNTs while poly(2‐naphthylmethacrylate) (PNMA) preferentially disperses metallic SWNTs, all in dimethylforamide (DMF). Photoluminescence excitation (PLE) spectroscopy indicates that all three polymers preferentially disperse smaller‐diameter SWNTs, particularly those of (6,5) chirality, in DMF. When chloroform is used instead of DMF, the larger‐diameter SWNTs (8,4) and (7,6) are instead selected by PNMA. The solvent effects suggest that diameter selectivity and change of polymer conformation is probably responsible. Change of the polymer fluorescence upon interaction with SWNTs indicates that metallicity selectivity presumably results from the photon‐induced dipole–dipole interaction between polymeric chromophore and SWNTs. Thin‐film FET devices using semiconductor‐enriched solution with PMMAFA have been successfully fabricated and the device performance confirms the sem‐SWNTs enrichment with a highly reproducible on/off ratio of about 10³.     

Designing Catalysts for Chirality‐Selective Synthesis of Single‐Walled Carbon Nanotubes: Past Success and Future Opportunity

A major obstacle for the applications of single‐walled carbon nanotubes (SWNTs) in electronic devices is their structural diversity, ending in SWNTs with diverse electrical properties. Catalytic chemical vapor deposition has shown great promise in directly synthesizing high‐quality SWNTs with a high selectivity to specific chirality (n, m). During the growth process, the tube–catalyst interface plays crucial roles in regulating the SWNT nucleation thermodynamics and growth kinetics, ultimately governing the SWNT chirality distribution. Starting with the introduction of SWNT growth modes, this review seeks to extend the knowledge about chirality‐selective synthesis by clarifying the energetically favored SWNT cap nucleation and the threshold step for SWNT growth, which describes how the tube–catalyst interface affects both the nucleus energy and the new carbon atom incorporation. Such understandings are subsequently applied to interpret the (n, m) specific growth achieved on a variety of templates, such as SWNT segments or predefined molecular seeds, transition metal (Fe, Co and Ni)‐containing catalysts at low reaction temperatures, W‐based alloy catalysts, and metal carbides at relatively high reaction temperatures. The up to date achievements on chirality‐controlled synthesis of SWNTs is summarized and the remaining major challenges existing in the SWNT synthesis field are discussed.     

A photovoltaic device based on a poly(phenyleneethynylene)/SWNT composite active layer

Although research on the use of single walled carbon nanotubes (SWNTs) as the acceptor in polymer photovoltaic cells is currently making great progress, their poor dispersion in a polymer matrix has greatly hindered the overall performance of the devices. Here a novel bulk heterojunction structure based on a poly(phenyleneethynylene)/SWNT composite was designed to improve the dispersion of SWNTs in the composite based on their structural similarity and strong interaction. Better dispersion and higher performance are achieved compared with a common control device based on a poly(3-octylthiophene)/SWNT composite layer.     

On‐Chip Chemical Self‐Assembly of Semiconducting Single‐Walled Carbon Nanotubes (SWNTs): Toward Robust and Scale Invariant SWNTs Transistors

In this paper, the fabrication of carbon nanotubes field effect transistors by chemical self‐assembly of semiconducting single walled carbon nanotubes (s‐SWNTs) on prepatterned substrates is demonstrated. Polyfluorenes derivatives have been demonstrated to be effective in selecting s‐SWNTs from raw mixtures. In this work the authors functionalized the polymer with side chains containing thiols, to obtain chemical self‐assembly of the selected s‐SWNTs on substrates with prepatterned gold electrodes. The authors show that the full side functionalization of the conjugated polymer with thiol groups partially disrupts the s‐SWNTs selection, with the presence of metallic tubes in the dispersion. However, the authors determine that the selectivity can be recovered either by tuning the number of thiol groups in the polymer, or by modulating the polymer/SWNTs proportions. As demonstrated by optical and electrical measurements, the polymer containing 2.5% of thiol groups gives the best s‐SWNT purity. Field‐effect transistors with various channel lengths, using networks of SWNTs and individual tubes, are fabricated by direct chemical self‐assembly of the SWNTs/thiolated‐polyfluorenes on substrates with lithographically defined electrodes. The network devices show superior performance (mobility up to 24 cm² V^?1 s^?1), while SWNTs devices based on individual tubes show an unprecedented (100%) yield for working devices. Importantly, the SWNTs assembled by mean of the thiol groups are stably anchored to the substrate and are resistant to external perturbation as sonication in organic solvents.     

Nanoscale Charge Percolation Analysis in Polymer‐Sorted (7,5) Single‐Walled Carbon Nanotube Networks

The current percolation in polymer‐sorted semiconducting (7,5) single‐walled carbon nanotube (SWNT) networks, processed from solution, is investigated using a combination of electrical field‐effect measurements, atomic force microscopy (AFM), and conductive AFM (C‐AFM) techniques. From AFM measurements, the nanotube length in the as‐processed (7,5) SWNTs network is found to range from ≈100 to ≈1500 nm, with a SWNT surface density well above the percolation threshold and a maximum surface coverage ≈58%. Analysis of the field‐effect charge transport measurements in the SWNT network using a 2D homogeneous random‐network stick‐percolation model yields an exponent coefficient for the transistors OFF currents of 16.3. This value is indicative of an almost ideal random network containing only a small concentration of metallic SWNTs. Complementary C‐AFM measurements on the other hand enable visualization of current percolation pathways in the xy plane and reveal the isotropic nature of the as‐spun (7,5) SWNT networks. This work demonstrates the tremendous potential of combining advanced scanning probe techniques with field‐effect charge transport measurements for quantification of key network parameters including current percolation, metallic nanotubes content, surface coverage, and degree of SWNT alignment. Most importantly, the proposed approach is general and applicable to other nanoscale networks, including metallic nanowires as well as hybrid nanocomposites.     

Fluorescent Polymer—Single‐Walled Carbon Nanotube Complexes with Charged and Noncharged Dendronized Perylene Bisimides for Bioimaging Studies

Fluorescent nanomaterials are expected to revolutionize medical diagnostic, imaging, and therapeutic tools due to their superior optical and structural properties. Their inefficient water solubility, cell permeability, biodistribution, and high toxicity, however, limit the full potential of their application. To overcome these obstacles, a water‐soluble, fluorescent, cytocompatible polymer—single‐walled carbon nanotube (SWNT) complex is introduced for bioimaging applications. The supramolecular complex consists of an alkylated polymer conjugated with neutral hydroxylated or charged sulfated dendronized perylene bisimides (PBIs) and SWNTs as a general immobilization platform. The polymer backbone solubilizes the SWNTs, decorates them with fluorescent PBIs, and strongly improves their cytocompatibility by wrapping around the SWNT scaffold. In photophysical measurements and biological in vitro studies, sulfated complexes exhibit superior optical properties, cellular uptake, and intracellular staining over their hydroxylated analogs. A toxicity assay confirms the highly improved cytocompatibility of the polymer‐wrapped SWNTs toward surfactant‐solubilized SWNTs. In microscopy studies the complexes allow for the direct imaging of the SWNTs' cellular uptake via the PBI and SWNT emission using the 1st and 2nd optical window for bioimaging. These findings render the polymer‐SWNT complexes with nanometer size, dual fluorescence, multiple charges, and high cytocompatibility as valuable systems for a broad range of fluorescence bioimaging studies.     

Magnetic orientation of single-walled carbon nanotubes or their composites using polymer wrapping

Abstract

The magnetic orientation of single-walled carbon nanotubes (SWNTs) or the SWNT composites wrapped with polymer using poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEHPPV) as the conducting polymer were examined. The formation of SWNT/MEHPPV composites was confirmed by examining absorption and fluorescence spectra. The N,N-dimethylformamide solution of SWNT/MEHPPV composites or the aqueous solution of the shortened SWNTs was introduced dropwise onto a mica or glass plate. The magnetic processing of the composites or the SWNTs was carried out using a superconducting magnet with a horizontal direction (8 T). The AFM images indicated that the SWNT/MEHPPV composites or the SWNTs were oriented randomly without magnetic processing, while with magnetic processing (8 T), they were oriented with the tube axis of the composites or the SWNTs parallel to the magnetic field. In polarized absorption spectra of SWNT/MEHPPV composites on glass plates without magnetic processing, the absorbance due to semiconducting SWNT in the near-IR region in horizontal polarized light was almost the same as that in vertical polarized light. In contrast, with magnetic processing (8 T), the absorbance due to semiconducting SWNT in the horizontal polarization direction against the direction of magnetic field was stronger than that in the vertical polarization direction. Similar results were obtained from the polarized absorption spectra for the shortened SWNTs. These results of polarized absorption spectra also support the magnetic orientation of the SWNT/MEHPPV composites or the SWNTs. On the basis of a comparison of the composites and the SWNTs alone, the magnetic orientation of SWNT/MEHPPV composites is most likely ascribable to the anisotropy in susceptibilities of SWNTs.     

Single-walled carbon nanotubes used as stationary phase in GC

Single-walled carbon nanotubes (SWNTs) have high surface area, high adsorption ability, and nanoscale interactions. In this study, capillary columns including SWNTs, ionic liquid (IL), and IL + SWNTs for GC were prepared. The separation results showed that SWNTs possessed a wide selectivity toward alkanes, alcohols, aromatic compounds, and ketones, and a SWNT capillary column was a very useful GC column for the separation of gas samples. Coating the IL stationary phase on the SWNT capillary column, the SWNTs were able to improve chromatographic characteristic of ionic liquid. Comparing the IL coated on three graphite carbon black capillary columns, which were prepared by dynamic coating, static coating, and chemical bonding the Carbopack C with on SWNTs capillary column, the capacity factors were much higher on the SWNT column. The SEM showed that SWNTs could be bonded to the inner surface of capillary tubing, and most of them were linked end-to-end to form a layer of network structure of skeletons resulting in a high surface area, which increased the interactions between stationary phase and analytes. This is the first single-wall carbon nanotubes bonded to the fused-silica capillary tubing. In the first approach, SWNTs assist ionic liquid with enhanced chromatographic characteristic in GC. This work indicates that SWNTs make it possible to extend the application range on the newly prepared chromatographic stationary phases for GC.     

Wafer‐Scale Fabrication of Suspended Single‐Walled Carbon Nanotube Arrays by Silver Liquid Dynamics

Suspended single‐walled carbon nanotubes (SWNTs) have advantages in mechanical resonators and highly sensitive sensors. Large‐scale fabrication of suspended SWNTs array devices and uniformity among SWNTs devices remain a great challenge. This study demonstrates an effective, fast, and wafer‐scale technique to fabricate suspended SWNT arrays, which is based on a dynamic motion of silver liquid to suspend and align the SWNTs between the prefabricated palladium electrodes in high temperature annealing treatment. Suspended, strained, and aligned SWNTs are synthesized on a 2 × 2 cm² substrate with an average density of 10 tubes per micrometer. Under the optimal conditions, almost all SWNTs become suspended. A promising formation model of suspended SWNTs is established. The Kelvin four‐terminal resistance measurement shows that these SWNT array devices have extreme low contact resistance. Meanwhile, the suspended SWNT array field effect transistors are fabricated by selective etching of metallic SWNTs using electrical breakdown. This method of large‐scale fabrication of suspended architectures pushes the study of nanoscale materials into a new stage related to the electrical physics and industrial applications.     

Engineering Supramolecular Polymer Conformation for Efficient Carbon Nanotube Sorting

Supramolecular polymer sorting is a promising approach to separating single‐walled carbon nanotubes (CNTs) by electronic type. Unlike conjugated polymers, they can be easily removed from the CNTs after sorting by breaking the supramolecular bonds, allowing for isolation of electronically pristine CNTs as well as facile recycling of the sorting polymer. However, little is understood about how supramolecular polymer properties affect CNT sorting. Herein, chain stoppers are used to engineer the conformation of a supramolecular sorting polymer, thereby elucidating the relationship between sorting efficacy and polymer conformation. Through NMR and UV–vis spectroscopy, small‐angle X‐ray scattering (SAXS), and thermodynamic modeling, it is shown that this supramolecular polymer exhibits ring–chain equilibrium, and that this equilibrium can be skewed toward chains by the addition of chain stoppers. Furthermore, by controlling the stopper–monomer ratio, the sorting yield can be doubled from 7% to 14% without compromising the semiconducting purity (>99%) or properties of sorted CNTs.     

Neurite Outgrowth on Nanocomposite Scaffolds Synthesized from PLGA and Carboxylated Carbon Nanotubes

Carbon nanotubes (CNTs) have been suggested as suitable materials for biomedical applications, especially in the neural area. It is essential not only to investigate the biocompatibility of CNTs with the neural system but also to determine proper methods for applying CNTs to neuronal growth. This work represents the first application of CNTs by electrospun poly(D ,L ‐lactic‐co‐glycolic acid) (PLGA) scaffolds for a neural system. We synthesized electrospun nanocomposites of PLGA and single‐walled carbon nanotubes functionalized by carboxylic acid groups (c‐SWNTs), and investigated neurite outgrowth from SH‐SY5Y cells on these nanocomposites as compared to that on fibrous PLGA alone. Cells on our PLGA/c‐SWNT nanocomposite showed significantly enhanced mitochondrial function and neurite outgrowth compared to cells on PLGA alone. We concluded that c‐SWNTs incorporated into fibrous PLGA scaffolds exerted a positive role on the health of neural cells.     

Measurement of strain distributions near the steel/epoxy interface by micro-Raman spectroscopy under tensile load condition

Micro-Raman spectroscopy was applied for evaluating the stress distributions in the vicinity of the interface of the steel/epoxy bonded joint under tensile loading condition. Herein, single-walled carbon nanotubes (SWNTs) embedded in a polymer can be used as a mechanical sensor, in which the position of the D* Raman band varies with the strain or stress transferred to SWNTs from the surrounding matrix. In order to evaluate the strain distributions, however, it is required to elucidate the effect of the multiaxial stress on the D* band shift, because a multiaxial stress field appears in the vicinity of the interface and, the validity of this method has been confirmed only under uniaxial loading condition. Hence, at first, the D* band shift of a bulk epoxy/SWNT composite was measured under biaxial loading condition using a cruciform-type specimen. It was found that the D* band shift could be standardized in terms of the strain in the polarized direction even though under the biaxial condition. Then, on the basis of the result, this method was applied for evaluating the strain distributions of the steel/SWNT composite bonded joints under uniaxial tensile loading condition. The observation indicated that the strain singularity appeared in the vicinity of the interface, similar to the results of the finite-element analysis, and the observed strain almost agreed with calculated one in the range of 0.03–10 mm distance from the interface.     

Structure‐Dependent Mitochondrial Dysfunction and Hypoxia Induced with Single‐Walled Carbon Nanotubes

Cytotoxicity of nanomaterials on living systems is known to be affected by their size, shape, surface chemistry, and other physicochemical properties. Exposure to a well‐characterized subpopulation of specific nanomaterials is therefore desired to reveal more detailed mechanisms. This study develops scalable density gradient ultracentrifugation sorting of highly dispersed single‐walled carbon nanotubes (SWNTs) into four distinct bands based on diameter, aggregation, and structural integrity, with greatly improved efficiency, yield, and reproducibility. With guarantee of high yield and stability of four SWNT fractions, it is possible for the first time, to investigate the structure‐dependent bioeffects of four SWNT fractions. it is possible Among these, singly‐dispersed integral SWNTs show no significant effects on the mitochondrial functions and hypoxia. The aggregated integral SWNTs show more significant effects on the mitochondrial dysfunction and hypoxia compared to the aggregated SWNTs with poor structure integrity. Then, it is found that the aggregated integral SWNTs induced the irregular mitochondria respiratory and pro‐apoptotic proteins activation, while aggregated SWNTs with poor structure integrity greatly enhanced reactive oxygen species (ROS) levels. This work supports the view that control of the distinct structure characteristics of SWNTs helps establish clearer structure‐bioeffect correlation and health risk assessment. It is also hoped that these results can help in the design of nanomaterials with higher efficiency and accuracy in subcellular translocation.     

Optical Absorption of Single‐Wall Carbon Nanotubes Produced by Arc‐Discharge Method with Different Concentration of Ni/Co Catalyst

Abstract

Material containing single‐wall carbon nanotubes (SWNTs) was obtained by arc‐discharge method. The optical absorption spectra were measured. Several narrow absorption bands were observed in a range from 0.4 to 3 eV caused by optical transitions between van Hove singularities. Comparing the results of “tight‐binding” electronic structure calculation for SWNT with the experimental spectra we found that each feature of spectrum can be attributed to interband transition in SWNTs. We have also found that the total yield of SWNTs and their diameter distribution depend on the catalyst content.     

Aligned,Ultralong Single‐Walled Carbon Nanotubes: From Synthesis,Sorting, to Electronic Devices

Aligned, ultralong single‐walled carbon nanotubes (SWNTs) represent attractive building blocks for nanoelectronics. The structural uniformity along their tube axis and well‐ordered two‐dimensional architectures on wafer surfaces may provide a straightforward platform for fabricating high‐performance SWNT‐based integrated circuits. On the way towards future nanoelectronic devices, many challenges for such a specific system also exist. This Review summarizes the recent advances in the synthesis, identification and sorting, transfer printing and manipulation, device fabrication and integration of aligned, ultralong SWNTs in detail together with discussion on their major challenges and opportunities for their practical application.     

Microwave‐Assisted Regeneration of Single‐Walled Carbon Nanotubes from Carbon Fragments

Direct growth of chirality‐controlled single‐walled carbon nanotubes (SWNTs) with metal catalyst free strategy, like cloning or epitaxial growth, has suffered from the low efficiency. The underlying problem is the activation of seed edge. Here an unexpectedly efficient microwave‐assisted pathway to regenerate SWNTs from carbon fragments on SiO₂/Si substrate is demonstrated via Raman spectroscopy and atomic force microscope (AFM) characterization. In this attempt, microwave irradiation provides fast heating to remove polar groups bonded to carbon nanotubes and reduce the spontaneous closure of tubes’ open ends. The survived SWNT and carbon fragments connected to it after plasma treatment are simply microwaved and then they serve as the template for regeneration. Scanning electron microscope and AFM characterizations indicate that the efficiency of the regeneration can reach 100%. And the regenerated SWNT has been proved without any change in chirality compared to the original SWNT. Electrical measurements on regenerated carbon nanotube films indicate 1 and 2 times increase in on/off ratio and on‐state current respectively than original carbon nanotube films obtained from solution‐phase separation, confirming the improvement of SWNT's quality. The microwave‐assisted regeneration is found to be highly effective and would be applied to improve the cloning efficiency of carbon nanotubes potentially.     

Multifunctional Composites of Ceramics and Single‐Walled Carbon Nanotubes

Polycrystalline ceramic/single‐walled carbon nanotube (SWNT) composites possess unique grain boundaries, containing 1D tortuous SWNTs bundles that form 2D tangled embedded nets. This unprecedented grain‐boundary structure allows tailoring of multifunctional ceramic/SWNTs composites with unique combinations of desirable mechanical (toughness, strength, creep) and transport (electrical, thermal) properties. A brief discussion and analysis of recent developments in these composites are presented.     

Hydrothermally Oxidized Single‐Walled Carbon Nanotube Networks for High Volumetric Electrochemical Energy Storage

Improving volumetric energy density is one of the major challenges in nanostructured carbon electrodes for electrochemical energy storage device applications. Herein, a simple hydrothermal oxidation process of single‐walled carbon nanotube (SWNT) networks in dilute nitric acid is reported, enabling simultaneous physical densification and chemical functionalization of the as‐assembled randomly‐packed SWNT films. After the hydrothermal oxidation process, the density of the SWNT films increases from 0.63 to 1.02 g cm^?3 and a considerable amount of redox‐active oxygen functional groups are introduced on the surface of the SWNTs. The functionalized SWNT films are used as positive electrodes against Li metal negative electrodes for potential Li‐ion capacitors or Li‐ion battery applications. The functionalized SWNT electrodes deliver high volumetric as well as gravimetric capacities, 154 Ah L^?1 and 152 mAh g^?1, respectively, owing to the surface redox reactions between the introduced oxygen functional groups and Li ions. In addition, these electrodes exhibit a remarkable rate‐capability by retaining its high capacity of 94 Ah L^?1 (92 mAh g^?1) at a high discharge rate of 10 A g^?1. These results demonstrate the simple hydrothermal oxidation process as an attractive strategy for improving the volumetric performance of nanostructured carbon electrodes.     

Functional Single‐Walled Carbon Nanotubes and Nanoengineered Networks for Organic‐ and Perovskite‐Solar‐Cell Applications

Carbon nanotubes have a variety of remarkable electronic and mechanical properties that, in principle, lend them to promising optoelectronic applications. However, the field has been plagued by heterogeneity in the distributions of synthesized tubes and uncontrolled bundling, both of which have prevented nanotubes from reaching their full potential. Here, a variety of recently demonstrated solution‐processing avenues is presented, which may combat these challenges through manipulation of nanoscale structures. Recent advances in polymer‐wrapping of single‐walled carbon nanotubes (SWNTs) are shown, along with how the resulting nanostructures can selectively disperse tubes while also exploiting the favorable properties of the polymer, such as light‐harvesting ability. New methods to controllably form nanoengineered SWNT networks with controlled nanotube placement are discussed. These nanoengineered networks decrease bundling, lower the percolation threshold, and enable a strong enhancement in charge conductivity compared to random networks, making them potentially attractive for optoelectronic applications. Finally, SWNT applications, to date, in organic and perovskite photovoltaics are reviewed, and insights as to how the aforementioned recent advancements can lead to improved device performance provided.     

Multiscale modeling for mechanical properties of carbon nanotube reinforced nanocomposites subjected to different types of loading

Multiscale modeling was presented for the nonlinear properties of polymer/single wall carbon nanotube (SWNT) nanocomposite under tensile, bending and torsional loading conditions. To predict the mechanical properties of both armchair and zigzag SWNTs, a finite element (FE) model based on the theory of molecular mechanics was used. For reducing the computational efforts, an equivalent cylindrical beam element was proposed, which has the unique advantage of describing the mechanical properties of SWNTs considering the nonlinearity of SWNT behavior. For a direct evaluation of the rigidities of the proposed equivalent beam, the data obtained through atomistic FE analyses of SWNT were fitted to six different equations, covering the three types of loading for both armchair and zigzag configurations. The proposed equivalent beam element was then used to build a cylindrical representative volume element (RVE) using which the effects of the interphase between SWNT and the polymer on the mechanical properties of RVE could be studied. It was found that while the interphase has a small effect on the nanocomposite stiffness, the ratio of (SWNT length)/(RVE length) dramatically affects the nanocomposite stiffness.