Carbon nanotube wires and cables: near-term applications and future perspectives

Strong Connection of Single-Wall Carbon Nanotube Fibers with a Copper Substrate Using an Intermediate Nickel Layer

Lightweight carbon nanotube fibers (CNTFs) with high electrical conductivity and high tensile strength are considered to be an ideal wiring medium for a wide range of applications. However, connecting CNTFs with metals by soldering is extremely difficult due to the nonreactive nature and poor wettability of CNTs. Here we report a strong connection between single-wall CNTFs (SWCNTFs) and a Cu matrix by introducing an intermediate Ni layer, which enables the formation of mechanically strong and electrically conductive joints between SWCNTFs and a eutectic Sn-37Pb alloy. The electrical resistance change rate (ΔR/R0) of Ni-SWCNTF/solder-Cu interconnects only decreases ∼29.8% after 450 thermal shock cycles between temperatures of -196 and 150 °C, which is 8.2 times lower than that without the Ni layer. First-principles calculations indicate that the introduction of the Ni layer significantly improves the heterogeneous interfacial bond strength of the Ni-SWCNTF/solder-Cu connections.

Electrical conductivity of a single parallel contact between carbon nanotubes

Interfacial resistance plays a critical role in the transport properties of nanomaterial-based assemblies. However, understanding of them remains limited due to the difficulty of experimental approaches. Here we report in situ measurements of the electrical resistance of a single parallel contact between carbon nanotubes. By varying the contact length systematically, we derive the electrical conductivities of carbon nanotubes and interfaces. The interface between nanotubes exhibits conductivity intermediate between those of pyrolytic and single-crystal graphite. The threshold contact length between interface- and bulk-dominant electrical transport is quantitatively estimated.

Recent Advances in Metal/Alloy Nano Coatings for Carbon Nanotubes Based on Electroless Plating

A large number of researches on the electroless plating of carbon nanotubes and their applications after plating have emerged, which has attracted more and more attention. In this review article, the existing electroless plating methods for carbon nanotubes were briefly summarized, and the surface coatings were listed and analyzed in detail. At last, the related applications after electroless metal/alloy coatings of carbon nanotubes were discussed in detail. This study aims to provide a reference for the research and improvement of different electroless metals/alloys coatings of carbon nanotubes. After a clear understanding of the electroless metal/alloy coatings of carbon nanotubes, the appropriate coating can be selected according to the actual situation, so that the carbon nanotubes after plating can be used as reinforcement and modification materials for better satisfaction of the needs, and the application of plated carbon nanotubes has reference significance in more fields.

From Waste Plastics to Carbon Nanotube Audio Cables

Carbon nanotubes (CNTs) have long been at the forefront of materials research, with applications ranging from composites for increased tensile strength in construction and sports equipment to transistor switches and solar cell electrodes in energy applications. There remains untapped potential still when it comes to energy and data transmission, with our group having previously demonstrated a working ethernet cable composed of CNT fibers. Material composition, electrical resistance, and electrical capacitance all play a strong role in the making of high-quality microphone and headphone cables, and the work herein describes the formation of a proof-of-concept CNT audio cable. Testing was done compared to commercial cables, with frequency response measurements performed for further objective testing. The results show performance is on par with commercial cables, and the CNTs being grown from waste plastics as a carbon source further adds to the value proposition, while also being environmentally friendly.

On the Use of Carbon Cables from Plastic Solvent Combinations of Polystyrene and Toluene in Carbon Nanotube Synthesis

For every three people on the planet, there are approximately two Tonnes (Te) of plastic waste. We show that carbon recovery from polystyrene (PS) plastic is enhanced by the coaddition of solvents to grow carbon nanotubes (CNTs) by liquid injection chemical vapour deposition. Polystyrene was loaded up to 4 wt% in toluene and heated to 780 °C in the presence of a ferrocene catalyst and a hydrogen/argon carrier gas at a 1:19 ratio. High resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Raman spectroscopy were used to identify multiwalled carbon nanotubes (MWCNTs). The PS addition in the range from 0 to 4 wt% showed improved quality and CNT homogeneity; Raman "Graphitic/Defective" (G/D) values increased from 1.9 to 2.3; mean CNT diameters increased from 43.0 to 49.2 nm; and maximum CNT yield increased from 11.37% to 14.31%. Since both the CNT diameters and the percentage yield increased following the addition of polystyrene, we conclude that carbon from PS contributes to the carbon within the MWCNTs. The electrical contact resistance of acid-washed Bucky papers produced from each loading ranged from 2.2 to 4.4 Ohm, with no direct correlation to PS loading. Due to this narrow range, materials with different loadings were mixed to create the six wires of an Ethernet cable and tested using iPerf3; the cable achieved up- and down- link speeds of ~99.5 Mbps, i.e., comparable to Cu wire with the same dimensions (~99.5 Mbps). The lifecycle assessment (LCA) of CNT wire production was compared to copper wire production for a use case in a Boeing 747-400 over the lifespan of the aircraft. Due to their lightweight nature, the CNT wires decreased the CO₂ footprint by 21 kTonnes (kTe) over the aircraft's lifespan.

Carbon Nanotube Reinforced Strong Carbon Matrix Composites

As an excellent candidate for lightweight structural materials and nonmetal electrical conductors, carbon nanotube reinforced carbon matrix (CNT/C) composites have potential use in technologies employed in aerospace, military, and defense endeavors, where the combinations of light weight, high strength, and excellent conductivity are required. Both polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods have been widely studied for CNT/C composite fabrications with diverse focuses and various modifications. Progress has been reported to optimize the performance of CNT/C composites from broad aspects, including matrix densification, CNT alignment, microstructure control, and interface engineering, etc. Recent approaches, such as using resistance heating for PIP or CVI, contribute to the development of CNT/C composites. To deliver a timely and up-to-date overview of CNT/C composites, we have reviewed the most recent trends in fabrication processes, summarized the mechanical reinforcement mechanism, and discussed the electrical and thermal properties, as well as relevant case studies for high-temperature applications. Conclusions and perspectives addressing future routes for performance optimization are also presented. Hence, this review serves as a rundown of recent advances in CNT/C composites and will be a valuable resource to aid future developments in this field.

A seed-mediated growth of gold nanoparticles inside carbon nanotube fibers for fabrication of multifunctional nanohybrid fibers with enhanced mechanical and electrical properties

The seed-mediated growth strategy of Au nanoparticles (Au NPs) inside carbon nanotube (CNT) fibers is demonstrated to greatly improve their mechanical and electrical properties and provide a function for catalytic applications. The resulting Au NP@CNT nanocomposite fibers exhibit 100% knot efficiency, catalytic activity and considerably enhanced modulus, tensile strength, and electrical conductivity from 7 GPa, 109 MPa and 1300 S cm-1 to 24 GPa, 351 MPa and 3600 S cm-1, respectively. The enhancement mechanism is also revealed by systematic characterization and theoretical simulations.

Enrichment of Metallic Carbon Nanotubes Using a Two-Polymer Extraction Method

The large-scale enrichment of metallic carbon nanotubes is a challenging goal that has proven elusive. Selective dispersion of carbon nanotubes by specifically designed conjugated polymers is effective for isolating semiconducting species, but a comparable system does not exist for isolating metallic species. Here, we report a two-polymer system where semiconducting species are extracted from the raw HiPCO or plasma-torch nanotube starting material using an electron-rich poly(fluorene-co-carbazole) derivative, followed by isolation of the metallic species remaining in the residue using an electron-poor methylated poly(fluorene-co-pyridine) polymer. Characterization of the electronic nature of extracted samples was carried out via a combination of absorption, Raman, and fluorescence spectroscopy, as well as electrical conductivity measurements. Using this methodology, the metallic species in the sample were enriched 2-fold in comparison to the raw starting material. These results indicate that the use of electron-poor polymers is an effective strategy for the enrichment of metallic species.

Splash-Resistant and Light-Weight Silk-Sheathed Wires for Textile Electronics

Silk has outstanding mechanical properties and biocompatibility. It has been used to fabricate traditional textiles for thousands of years and can be produced in large scale. Silk materials are potentially attractive in modern textile electronics. However, silk is not electrically conductive, thus limiting its applications in electronics. Moreover, regenerated silk is generally rigid and brittle, which hinder post processing. Here we report the fabrication of conductive silk wire in which carbon nanotube (CNT) yarns are wrapped with fluffy and flexible silk nanofiber films. The silk nanofiber film was prepared by electrospinning and then wrapped around a rotating CNT yarn in situ. The obtained silk-sheathed CNT (CNT@Silk) wire has an insulating sheath, which protects the body against electrical shock. In addition, the fabricated wires exhibit a high electrical conductivity (3.1 × 10⁴ S/m), good mechanical strength (16 cN/tex), excellent flexibility, and high durability. More importantly, the wires have an extremely low density (2.0-7.8 × 10⁴ g/m3), which is 2 orders of magnitude lower than that of the traditional metal wire (for example, Cu). Moreover, the wires display a good resistance to humidity, and a simple post treatment can make the wires splash-resistant, thereby expanding its applications. On the basis of these features, we demonstrate the use of the lightweight CNT@Silk wires in smart clothes, including electrochromism and near-field communication.

Aqueous electromigration of single-walled carbon nanotubes and co-electromigration with copper ions

The electromigration behaviour of raw and acid purified single walled carbon nanotubes (SWCNTs) in dilute aqueous systems (0.0034 mg mL^-1), in the absence of surfactant, with the addition of either 0.85 M acetic acid or 0.1 M CuSO₄, was evaluated using a 2-inch copper cathode and either a 2-inch copper or 0.5-inch platinum anode. The results showed that the electromigration of raw SWCNTs (with a high catalyst residue) in the presence of CuSO₄ resulted in the formation of a Cu-SWCNT composite material at the cathode. In contrast, acid purified SWCNTs were observed to diffuse to a copper anode, creating fibrillated agglomerates with "rice-grain"-like morphologies. Upon acidification with acetic acid (or addition of CuSO₄) the direction of electromigration reversed towards the cathode as a result of coordination of Cu²⁺ to the functional groups on the SWCNT overcoming the inherent negative charge of the acid purified SWCNTs. The result was the co-deposition of SWCNTs and Cu metal on the cathode. Addition of 0.005 M EDTA sequesters some of the Cu²⁺ and resulted in the separation of metal decorated SWCNTs to the cathode and un-decorated SWCNTs to the anode. The resulting SWCNT and Cu/SWCNT deposits were characterized by Raman spectroscopy, XPS, SEM, EDS, and TEM.

Copper/carbon nanotube composites: research trends and outlook

We present research progress made in developing copper/carbon nanotube composites (Cu/CNT) to fulfil a growing demand for lighter copper substitutes with superior electrical, thermal and mechanical performances. Lighter alternatives to heavy copper electrical and data wiring are needed in automobiles and aircrafts to enhance fuel efficiencies. In electronics, better interconnects and thermal management components than copper with higher current- and heat-stabilities are required to enable device miniaturization with increased functionality. Our literature survey encouragingly indicates that Cu/CNT performances (electrical, thermal and mechanical) reported so far rival that of Cu, proving the material's viability as a Cu alternative. We identify two grand challenges to be solved for Cu/CNT to replace copper in real-life applications. The first grand challenge is to fabricate Cu/CNT with overall performances exceeding that of copper. To address this challenge, we propose research directions to fabricate Cu/CNT closer to ideal composites theoretically predicted to surpass Cu performances (i.e. those containing uniformly distributed Cu and individually aligned CNTs with beneficial CNT-Cu interactions). The second grand challenge is to industrialize and transfer Cu/CNT from lab bench to real-life use. Toward this, we identify and propose strategies to address market-dependent issues for niche/mainstream applications. The current best Cu/CNT performances already qualify for application in niche electronic device markets as high-end interconnects. However, mainstream Cu/CNT application as copper replacements in conventional electronics and in electrical/data wires are long-term goals, needing inexpensive mass-production by methods aligned with existing industrial practices. Mainstream electronics require cheap CNT template-making and electrodeposition procedures, while data/electrical cables require manufacture protocols based on co-electrodeposition or melt-processing. We note (with examples) that initiatives devoted to Cu/CNT manufacturing for both types of mainstream applications are underway. With sustained research on Cu/CNT and accelerating its real-life application, we expect the successful evolution of highly functional, efficient, and sustainable next-generation electrical and electronics systems.

Electronic properties of carbon nanotubes complexed with a DNA nucleotide

Electronic properties of carbon nanotubes (CNTs) play an important role in their interactions with nano-structured materials. In this work, interactions of adenosine monophosphate (AMP), a DNA nucleotide, with metallic and semi-conducting CNTs are studied using the density functional tight binding (DFTB) method. The electronic structure of semi-conducting CNTs was found to be changed as they turned to metallic CNTs in a vacuum upon interaction with the nucleotide while metallic CNTs remain metallic. Specifically, the band gap of semi-conducting CNTs was decreased by 0.79 eV on average while nearly no change was found in the metallic tubes. However, our investigations showed that the presence of explicit water molecules prevents the metallicity change and only small changes in the CNT band gap occur. According to our charge analysis, the average negative charge accumulated on CNTs upon interaction with the AMP was determined to be 0.77 e in a vacuum while it was 0.03 e in solution. Therefore, it is essential to include explicit water molecules in simulating complexes formed by DNA nucleotides and CNTs which were ignored in several past studies performed using quantum mechanical approaches.

Electrical performance of lightweight CNT-Cu composite wires impacted by surface and internal Cu spatial distribution

We report ultralong conducting lightweight multiwall carbon nanotube (MWCNT)-Cu composite wires with MWCNTs uniformly distributed in a continuous Cu matrix throughout. With a high MWCNT vol% (40-45%), the MWCNT-Cu wire density was 2/3rd that of Cu. Our composite wires show manufacturing potential because we used industrially compatible Cu electrodeposition protocols on commercial CNT wires. Further, we systematically varied Cu spatial distribution on the composite wire surface and bulk and measured the associated electrical performance, including resistivity (ρ), temperature dependence of resistance, and stability to current (measured as current carrying capacity, CCC in vacuum). We find that a continuous Cu matrix with homogeneous MWCNT distribution, i.e., maximum internal Cu filling within MWCNT wires, is critical to high overall electrical performances. Wires with maximum internal Cu filling exhibit (i) low room temperature ρ, 1/100th of the starting MWCNT wires, (ii) suppressed resistance-rise with temperature-increase and temperature coefficient of resistance (TCR) ½ that of Cu, and (iii) vacuum-CCC 28% higher than Cu. Further, the wires showed real-world applicability and were easily soldered into practical circuits. Hence, our MWCNT-Cu wires are promising lightweight alternatives to Cu wiring for weight-reducing applications. The low TCR is specifically advantageous for stable high-temperature operation, e.g., in motor windings.

Understanding the Effect of Functional Groups on the Seeded Growth of Copper on Carbon Nanotubes for Optimizing Electrical Transmission

We present a study of the seeded growth of copper on the surface of two classes of single-walled carbon nanotubes (SWNTs) in order to compare the effects of surface functional groups. Pyridine-functionalized HiPco SWNTs and ultrashort SWNTs (US-SWNTs) were synthesized (py-SWNTs and py-US-SWNTs, respectively), and the functionality was used as seed sites for copper, via an aqueous electroless deposition reaction, as a comparison to the carboxylic acid functionality present on piranha-etched SWNTs and the native US-SWNTs. UV-vis spectroscopy demonstrated the take-up of Cu(II) ions by the functionalized SWNTs. TEM showed that the SWNTs with pyridine functionality more rapidly produced a more even distribution of copper seeds with a narrower size distribution (3-12 nm for py-US-SWNTs) than those SWNTs with oxygen functional groups (ca. 30 nm), showing the adventitious role of the pyridine functional group in the seeding process. Seed composition was confirmed as Cu(0) by XPS and SAED. Copper growth rate and morphology were shown to be affected by degree of pyridine functionality, the length of the SWNT, and the electroless reaction solvent used.

High-performance hybrid carbon nanotube fibers for wearable energy storage

Wearable energy storage devices are of practical interest, but few have been commercially exploited. Production of electrodes with extended cycle life, as well as high energy and power densities, coupled with flexibility, remains a challenge. Herein, we have demonstrated the development of a high-performance hybrid carbon nanotube (CNT) fiber-based supercapacitor for the first time using conventional wet-spinning processes. Manganese dioxide (MnO₂) nanoflakes were deposited onto the as-prepared CNT fibers by electrodeposition to form highly flexible nanocomposites fibers. As-prepared fibers were characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It was found that the specific capacitance was over 152 F g^-1 (156 F cm^-3), which is about 500% higher than the multi-walled carbon nanotube/MnO₂ yarn-based supercapacitors. The measured energy density was 14.1 Wh kg^-1 at a power density of 202 W kg^-1. These values are 232% and 32% higher than the energy density and power density of MWNT/MnO₂ yarn-based supercapacitor, respectively. It was found that the cyclic retention ability was more stable, revealing a 16% increase after 10 000 cycles. Such substantial enhancements of key properties of the hybrid material can be associated with the synergy of CNT and MnO₂ nanoparticles in the fiber structure. The use of wet-spun hybrid CNT for fiber-based supercapacitors has been demonstrated.

Graphene and Other 2D Colloids: Liquid Crystals and Macroscopic Fibers

Two-dimensional colloidal nanomaterials are running into renaissance after the enlightening researches of graphene. Macroscopic one-dimensional fiber is an optimal ordered structural form to express the in-plane merits of 2D nanomaterials, and the formation of liquid crystals (LCs) allows the creation of continuous fibers. In the correlated system from LCs to fibers, understanding their macroscopic organizing behavior and transforming them into new solid fibers is greatly significant for applications. Herein, we retrospect the history of 2D colloids and discuss about the concept of 2D nanomaterial fibers in the context of LCs, elaborating the motivation, principle and possible strategies of fabrication. Then we highlight the creation, development and typical applications of graphene fibers. Additionally, the latest advances of other 2D nanomaterial fibers are also summarized. Finally, conclusions, challenges and perspectives are provided to show great expectations of better and more fibrous materials of 2D nanomaterials. This review gives a comprehensive retrospect of the past century-long effort about the whole development of 2D colloids, and plots a clear roadmap - "lamellar solid - LCs - macroscopic fibers - flexible devices", which will certainly open a new era of structural-multifunctional application for the conventional 2D colloids.

Synthesis and properties of flexible nanocable with carbon nanotube @ polymer hierarchical structure

A multi-functional polymer-carbon nanotube (CNT) nanocable with a hierarchical structure is fabricated by grafting poly (glycidyl methacrylate) (PGMA) from the CNT surface via activators regenerated by electron transfer atom transfer radical polymerization. Multiple CNTs are arranged in parallel in the fabricated nanocable and exhibit strong binding force with sheathing PGMA. In situ mechanical and electrical tests conducted on an individual nanocable reveal its high flexibility and excellent surface insulation, with an electrical resistance of approximately 1 GΩ. On increasing the voltage to the nanocable's electrical breakdown point, nanoscale electrical trees are observed. Such degradation behavior is discussed in the wider context of breakdown mechanisms in polymer based CNTs.

Novel Strategy for One-Pot Synthesis of Gold Nanoplates on Carbon Nanotube Sheet As an Effective Flexible SERS Substrate

In this work, we demonstrate a novel route for one-pot synthesis of two-dimensional gold nanoplates (2-D AuNPLs) on carbon nanotube (CNT) sheet. Well-defined AuNPLs are grafted onto CNT sheet via a facile hydrothermal reduction process, during which bromine ions are employed as the surfactant for gold anisotropic growth. Scanning electron microscopy (SEM) shows large-scale AuNPLs with micrometer-scaled length and sub-100 nm thickness are deposited uniformly on the CNT sheet. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) results confirm the synthesized AuNPLs are single-crystalline with preferential {111} orientation. Based on the CNT sheet/AuNPLs hybrid, we have fabricated a flexible surface-enhanced Raman scattering (SERS) substrate, which can effectively detect the analyte Rhodamine 6G (Rh6G) at the concentration as low as 1 × 10^-7 M. The excellent SERS performance of this novel flexible substrate is mainly attributed to nanoscaled gaps between the neighbors, large surface area with roughness, and their sharp edges and corners.

Chemical Strategies for Enhancing Activity and Charge Transfer in Ultrathin Pt Nanowires Immobilized onto Nanotube Supports for the Oxygen Reduction Reaction

Multiwalled carbon nanotubes (MWNTs) represent a promising support medium for electrocatalysts, especially Pt nanoparticles (NPs). The advantages of using MWNTs include their large surface area, high conductivity, as well as long-term stability. Surface functionalization of MWNTs with various terminal groups, such as -COOH, -SH, and -NH₂, allows for rational electronic tuning of catalyst-support interactions. However, several issues still need to be addressed for such systems. First, over the course of an electrochemical run, catalyst durability can decrease, due in part to metal NP dissolution, a process facilitated by the inherently high surface defect concentration within the support. Second, the covalent functionalization treatment of MWNTs adopted by most groups tends to lead to a loss of structural integrity of the nanotubes (NTs). To mitigate for all of these issues, we have utilized two different attachment approaches (i.e., covalent versus noncovalent) to functionalize the outer walls of pristine MWNTs and compared the catalytic performance of as-deposited ultrathin (<2 nm) 1D Pt nanowires with that of conventional Pt NPs toward the oxygen reduction reaction (ORR). Our results demonstrated that the electrochemical activity of Pt nanostructures immobilized onto functionalized carbon nanotube (CNT) supports could be dramatically improved by using ultrathin Pt nanowires (instead of NPs) with noncovalently (as opposed to covalently) functionalized CNT supports. Spectroscopic evidence corroborated the definitive presence of charge transfer between the metal catalysts and the underlying NT support, whose direction and magnitude are a direct function of (i) the terminal chemistry as well as (ii) the attachment methodology, both of which simultaneously impact upon the observed electrocatalytic performance. Specifically, the use of a noncovalent π-π stacking method coupled with a -COOH terminal moiety yielded the highest performance results, reported to date, for any similar system consisting of Pt (commercial NPs or otherwise) deposited onto carbon-based supports, a finding of broader interest toward the fabrication of high-performing electrocatalysts in general.

Carbon-Nanotube Fibers for Wearable Devices and Smart Textiles

Carbon-nanotube (CNT) fibers integrate such properties as high mechanical strength, extraordinary structural flexibility, high thermal and electrical conductivities, novel corrosion and oxidation resistivities, and high surface area, which makes them a very promising candidate for next-generation smart textiles and wearable devices. A brief review of the preparation of CNT fibers and recently developed CNT-fiber-based flexible and functional devices, which include artificial muscles, electrochemical double-layer capacitors, lithium-ion batteries, solar cells, and memristors, is presented.

Superb Electrically Conductive Graphene Fibers via Doping Strategy

Graphene fibers (GFs) with superb electrical conductivity are produced via a chemical doping strategy. The electrical conductivities reach up to 0.77 × 10⁷ -2.24 × 10⁷ S m^-1 , which are the highest values among all the reported GFs. The combination of lightness, superb conductivity, and easy scalability makes GFs a promising new carbonaceous fiber species with high performance and advanced functionality.

Carbon Nanotube Thin-Film Antennas

Multiwalled carbon nanotube (MWCNT) and single-walled carbon nanotube (SWCNT) dipole antennas have been successfully designed, fabricated, and tested. Antennas of varying lengths were fabricated using flexible bulk MWCNT sheet material and evaluated to confirm the validity of a full-wave antenna design equation. The ∼20× improvement in electrical conductivity provided by chemically doped SWCNT thin films over MWCNT sheets presents an opportunity for the fabrication of thin-film antennas, leading to potentially simplified system integration and optical transparency. The resonance characteristics of a fabricated chlorosulfonic acid-doped SWCNT thin-film antenna demonstrate the feasibility of the technology and indicate that when the sheet resistance of the thin film is >40 ohm/sq no power is absorbed by the antenna and that a sheet resistance of <10 ohm/sq is needed to achieve a 10 dB return loss in the unbalanced antenna. The dependence of the return loss performance on the SWCNT sheet resistance is consistent with unbalanced metal, metal oxide, and other CNT-based thin-film antennas, and it provides a framework for which other thin-film antennas can be designed.

Lightweight, Flexible, High-Performance Carbon Nanotube Cables Made by Scalable Flow Coating

Coaxial cables for data transmission are ubiquitous in telecommunications, aerospace, automotive, and robotics industries. Yet, the metals used to make commercial cables are unsuitably heavy and stiff. These undesirable traits are particularly problematic in aerospace applications, where weight is at a premium and flexibility is necessary to conform with the distributed layout of electronic components in satellites and aircraft. The cable outer conductor (OC) is usually the heaviest component of modern data cables; therefore, exchanging the conventional metallic OC for lower weight materials with comparable transmission characteristics is highly desirable. Carbon nanotubes (CNTs) have recently been proposed to replace the metal components in coaxial cables; however, signal attenuation was too high in prototypes produced so far. Here, we fabricate the OC of coaxial data cables by directly coating a solution of CNTs in chlorosulfonic acid (CSA) onto the cable inner dielectric. This coating has an electrical conductivity that is approximately 2 orders of magnitude greater than the best CNT OC reported in the literature to date. This high conductivity makes CNT coaxial cables an attractive alternative to commercial cables with a metal (tin-coated copper) OC, providing comparable cable attenuation and mechanical durability with a 97% lower component mass.

Enhanced Electrical Conductivity in Extruded Single-Wall Carbon Nanotube Wires from Modified Coagulation Parameters and Mechanical Processing

Single-wall carbon nanotubes (SWCNTs) synthesized via laser vaporization have been dispersed using chlorosulfonic acid (CSA) and extruded under varying coagulation conditions to fabricate multifunctional wires. The use of high purity SWCNT material based upon established purification methods yields wires with highly aligned nanoscale morphology and an over 4× improvement in electrical conductivity over as-produced SWCNT material. A series of eight liquids have been evaluated for use as a coagulant bath, and each coagulant yielded unique wire morphology based on its interaction with the SWCNT-CSA dispersion. In particular, dimethylacetamide as a coagulant bath is shown to fabricate highly uniform SWCNT wires, and acetone coagulant baths result in the highest specific conductivity and tensile strength. A 2× improvement in specific conductivity has been measured for SWCNT wires following tensioning induced both during extrusion via increased coagulant bath depth and during solvent evaporation via mechanical strain, over that of as-extruded wires from shallower coagulant baths. Overall, combination of the optimized coagulation parameters has yielded acid-doped wires with the highest reported room temperature electrical conductivities to date of 4.1-5.0 MS/m and tensile strengths of 210-250 MPa. Such improvements in bulk electrical conductivity can impact the adoption of metal-free, multifunctional SWCNT materials for advanced cabling architectures.

Thin-film electroencephalographic electrodes using multi-walled carbon nanotubes are effective for neurosurgery

Background

Intraoperative morphological and functional monitoring is essential for safe neurosurgery. Functional monitoring is based on electroencephalography (EEG), which uses silver electrodes. However, these electrodes generate metal artifacts as silver blocks X-rays, creating white radial lines on computed tomography (CT) images during surgery. Thick electrodes interfere with surgical procedures. Thus, thinner and lighter electrodes are ideal for intraoperative use.

Methods

The authors developed thin brain electrodes using carbon nanotubes that were formed into thin sheets and connected to electrical wires.

Results

The nanotube sheets were soft and fitted the curve of the head very well. When attached to the head using paste, the impedance of the newly developed electrodes was 5 kΩ or lower, which was similar to that of conventional metal electrodes. These electrodes can be used in combination with intraoperative CT, magnetic resonance imaging (MRI), or cerebral angiography. Somatosensory-evoked potentials, auditory brainstem responses, and visually evoked potentials were clearly identified in ten volunteers. The electrodes, without any artifacts that distort images, did not interfere with X-rays, CT, or MR images. They also did not cause skin damage.

Conclusions

Carbon nanotube electrodes may be ideal for neurosurgery.

Recent advances in understanding the reinforcing ability and mechanism of carbon nanotubes in ceramic matrix composites

Since the discovery of carbon nanotubes (CNTs), commonly referred to as ultimate reinforcement, the main purpose for fabricating CNT-ceramic matrix composites has been mainly to improve the fracture toughness and strength of the ceramic matrix materials. However, there have been many studies reporting marginal improvements or even the degradation of mechanical properties. On the other hand, those studies claiming noticeable toughening measured using indentation, which is an indirect/unreliable characterization method, have not demonstrated the responsible mechanisms applicable to the nanoscale, flexible CNTs; instead, those studies proposed those classical methods applicable to microscale fiber/whisker reinforced ceramics without showing any convincing evidence of load transfer to the CNTs. Therefore, the ability of CNTs to directly improve the macroscopic mechanical properties of structural ceramics has been strongly questioned and debated in the last ten years. In order to properly discuss the reinforcing ability (and possible mechanisms) of CNTs in a ceramic host material, there are three fundamental questions to our knowledge at both the nanoscale and macroscale levels that need to be addressed: (1) does the intrinsic load-bearing ability of CNTs change when embedded in a ceramic host matrix?; (2) when there is an intimate atomic-level interface without any chemical reaction with the matrix, could one expect any load transfer to the CNTs along with effective load bearing by them during crack propagation?; and (3) considering their nanometer-scale dimensions, flexibility and radial softness, are the CNTs able to improve the mechanical properties of the host ceramic matrix at the macroscale when individually, intimately and uniformly dispersed? If so, how? Also, what is the effect of CNT concentration in such a defect-free composite system? Here, we briefly review the recent studies addressing the above fundamental questions. In particular, we discuss the new reinforcing mechanism at the nanoscale responsible for unprecedented, simultaneous mechanical improvements and highlight the scalable processing method enabling the fabrication of defect-free CNT-concentered ceramics and CNT-graded composites with unprecedented properties. Finally, possible future directions will be briefly presented.

Polymer Coating of Carbon Nanotube Fibers for Electric Microcables

Carbon nanotubes (CNTs) are considered the most promising candidates to replace Cu and Al in a large number of electrical, mechanical and thermal applications. Although most CNT industrial applications require macro and micro size CNT fiber assemblies, several techniques to make conducting CNT fibers, threads, yarns and ropes have been reported to this day, and improvement of their electrical and mechanical conductivity continues. Some electrical applications of these CNT conducting fibers require an insulating layer for electrical insulation and protection against mechanical tearing. Ideally, a flexible insulator such as hydrogenated nitrile butadiene rubber (HNBR) on the CNT fiber can allow fabrication of CNT coils that can be assembled into lightweight, corrosion resistant electrical motors and transformers. HNBR is a largely used commercial polymer that unlike other cable-coating polymers such as polyvinyl chloride (PVC), it provides unique continuous and uniform coating on the CNT fibers. The polymer coated/insulated CNT fibers have a 26.54 μm average diameter—which is approximately four times the diameter of a red blood cell—is produced by a simple dip-coating process. Our results confirm that HNBR in solution creates a few microns uniform insulation and mechanical protection over a CNT fiber that is used as the electrically conducting core.

Macroscopic nanotube fibers spun from single-walled carbon nanotube polyelectrolytes

In this work, single-walled carbon nanotube (SWCNT) fibers were produced from SWCNT polyelectrolyte dispersions stabilized by crown ether in dimethyl sulfoxide and coagulated into aqueous solutions. The SWCNT polyelectrolyte dispersions had concentrations up to 52 mg/mL and showed liquid crystalline behavior under polarized optical microscopy. The produced SWCNT fibers are neat (i.e., not forming composites with polymers) and showed a tensile strength up to 124 MPa and a Young's modulus of 14 GPa. This tensile strength is comparable to those of SWCNT fibers spun from strong acids. Conductivities on the order of 10(4) S/m were obtained by doping the fibers with iodine.

Experimental evidence of rapid water transport through carbon nanotubes embedded in polymeric desalination membranes

As water molecules permeate ultrafast through carbon nanotubes (CNTs), many studies have prepared CNTs-based membranes for water purification as well as desalination, particularly focusing on high flux membranes. Among them, vertically aligned CNTs membranes with ultrahigh water flux have been successfully demonstrated for fundamental studies, but they lack scalability for bulk production and sufficiently high salt rejection. CNTs embedded in polymeric desalination membranes, i.e., polyamide thin-film composite (TFC) membranes, can improve water flux without any loss of salt rejection. This improved flux is achieved by enhancing the dispersion properties of CNTs in diamine aqueous solution and also by using cap-opened CNTs. Hydrophilic CNTs were prepared by wrapping CNT walls via bio-inspired surface modification using dopamine solution. Cap-opening of pristine CNTs is performed by using a thermo-oxidative process. As a result, hydrophilic, cap-opened CNTs-embedded polyamide TFC membranes are successfully prepared, which show much higher water flux than pristine polyamide TFC membrane. On the other hand, less-disperse, less cap-opened CNTs-embedded TFC membranes do not show any flux improvement and rather lead to lower salt rejection properties.

Nanorobotic Applications in Medicine: Current Proposals and Designs

Advances in technology have increased our ability to manipulate the world around us on an ever-decreasing scale. Nanotechnologies are rapidly emerging within the realm of medicine, and this subfield has been termed nanomedicine. Use of nanoparticle technology has become familiar and increasingly commonplace, especially with pharmaceutical technology. An exciting and promising area of nanotechnological development is the building of nanorobots, which are devices with components manufactured on the nanoscale. This area of study is replete with potential applications, many of which are currently being researched and developed. The goal of this paper is to give an introduction to the emerging field of nanorobotics within medicine, and provide a review of the emerging applications of nanorobotics to fields ranging from neurosurgery to dentistry.

One-Step Synthesis and High-Efficiency Decoloration of Multifunctional Porous-C/Fe3 O4 Nanospheres by Using a Sandwich-Structured Precursor with Three Roles

A new strategy for the one-step synthesis of multifunctional porous-C/Fe₃ O₄ nanospheres has been successfully developed by using ferrocenyl formic acid as a precursor. Based on its special structure, this sandwich structural precursor of ferrocenyl formic acid plays three roles in the synthesis process: it simultaneously serves as the carbon and iron source, templating agent, and pore-forming agent. The proposed synthesis is corroborated by characterization through SEM, TEM, XRD, FTIR spectroscopy, Raman spectroscopy, BET surface area measurements, BJH distributions, and vibrating sample magnetometry. The average diameter of as-synthesized porous-C/Fe₃ O₄ nanospheres is about 400 nm. Because of the porous structure of carbon nanospheres and its surface plasmon resonance with attached Fe₃ O₄ nanoparticles, the as-synthesized porous-C/Fe₃ O₄ nanospheres exhibit high activity toward the decoloration of rhodamine B. In addition, the resultant composites present ferromagnetic behavior with a magnetization saturation of 13.76 emu g^-1 , can be easily separated and recycled by an external magnet field for use in a variety of applications.

Unprecedented simultaneous enhancement in strain tolerance, toughness and strength of Al2O3 ceramic by multiwall-type failure of a high loading of carbon nanotubes

Carbon nanotubes (CNTs) have a remarkable load-bearing ability. Recently, however, multi-walled CNTs (MWCNTs) have been shown to possess dramatically higher load-bearing ability when intimately embedded in an oxide ceramic (Al2O3), because the load could be transferred not to only their outermost walls but also their generally unloaded inner walls via the strong interwall shear resistance originating from residual compressive stresses. This phenomenon is characterized by an uncommon, highly energy-dissipating, multiwall-type failure of individual MWCNTs during hybrid fracture, with no evidence of pullout. Here, we demonstrate that this nanoscale in-MWCNT load-transfer process, at an optimized, high loading of MWCNTs (10 vol%) and in a pore-free and uniform platform, leads to unprecedented, dramatic simultaneous enhancement in strain tolerance (81%), fracture toughness (52.2%), and flexural strength (22%) of the Al2O3 ceramic matrix. The extent of toughening by this mechanism is also the highest ever reported. This unprecedented performance by using a high loading of functional MWCNTs, namely, toughening, strengthening, softening and lightening, simultaneously and at this level, has implications for many functional and structural applications.

Highly concentrated 3D macrostructure of individual carbon nanotubes in a ceramic environment

A highly concentrated 3D macrostructure of individual multiwalled carbon nanotubes (MWCNTs) is practically realized in a ceramic environment with poreless/intimate interfaces by a scalable aqueous colloidal approach. This concept dramatically improves not only the transport property and network connectivity of the MWCNT 3D macrostructures (a DC-conductivity of nearly 5000 S m(-1) ) but also the strain tolerance of the ceramic environment. Such low-cost and novel MWCNT/ceramic hybrids have many potential functional and structural applications.

Effect of functional groups on the radial collapse and elasticity of carbon nanotubes under hydrostatic pressure

The effect of functional groups on the radial collapse and elasticity of a single-walled carbon nanotube (SWNT) under hydrostatic pressure was investigated using molecular dynamics and molecular mechanics simulations. It is found that the radial collapse and elasticity of the chemically modified SWNTs strongly depend on the polarity of the functional groups and the degree of functionalization. The results show that the fluorine modified SWNT (F-SWNT), on which 2.5-5.0% of the atoms are attached to -F groups, can sustain the original elasticity of the intrinsic SWNT, and the pressure needed to collapse the F-SWNT increases by 11.3-21.8%. Functional groups such as hydroxyl groups, amino groups and carboxylic groups can increase the pressure needed to collapse the modified SWNTs, but decrease their radial elasticity. Therefore, the F-SWNTs, due to the higher collapse pressure, are ideal fillers for nanocomposites for high load mechanical support.

High-performance, lightweight coaxial cable from carbon nanotube conductors

Coaxial cables have been constructed with carbon nanotube (CNT) materials serving as both the inner and outer conductors. Treatment of the CNT outer and inner conductors with KAuBr(4) was found to significantly reduce the attenuation of these cables, which demonstrates that chemical agents can be used to improve power transmission through CNT networks at high frequencies (150 kHz-3 GHz). For cables constructed with a KAuBr(4)-treated CNT outer conductor, power attenuation per length approaches parity with cables constructed from metallic conductors at significantly lower weight per length (i.e., 7.1 g/m for CNT designs compared to 38.8 g/m for an RG-58 design). A relationship between the thickness of the CNT outer conductor and the cable attenuation was observed and used to estimate the effective skin depth at high frequency. These results establish reliable, reproducible methods for the construction of coaxial cables from CNT materials that can facilitate further investigation of their performance in high-frequency transmission structures, and highlight a specific opportunity for significant reduction in coaxial cable mass.