Carbon Nanotube Sheets Research Articles

Tensile properties and fracture behavior of carbon nanotube-sheets/carbon fibers epoxy-impregnated bundle composites

An interesting technique for modifying carbon fiber-reinforced polymer matrix composites is through hybridization with carbon nanotubes (CNTs). Carbon nanotubes sheets/carbon fibers offer potential benefits of nanoscale reinforcement to the well-established fibrous composites by creating multiscale hybrid micro-nano composites. In this study, the tensile properties of high tensile strength polyacrylonitrile (PAN)- and high modulus pitch-based carbon fiber-reinforced polymer matrix composites incorporating CNT sheets (CNT-sh/CFs/Ep-H: CNT sheets/carbon fibers/epoxy hybrid composites) were investigated. To fabricate CNT sheets, CNT was vertically grown on a quartz glass plate by chemical vapor deposition. A solid-state drawing and winding technique was applied to transform the vertically aligned CNT array into horizontally aligned CNT sheets. The tensile modulus of the CNT-sh/CFs/Ep-H was higher than that of the composite in the as-received state (CFs/Ep: carbon fibers/epoxy bundle composite). The tensile strength of the CNT-sh/PAN-based CF/Ep-H was lower than that of the PAN-based CF/Ep, whereas the tensile strength of the CNT-sh/pitch-based CF/Ep-H was higher than that of the pitch-based CF/Ep.

Hierarchically porous, biaxially woven carbon nanotube sheet arrays for next-generation anion-exchange membrane water electrolyzers

A hierarchically porous, biaxially woven carbon nanotube sheet was proposed in a cathode of anion-exchange membrane water electrolysis to increase surface area and enhance transports.

Liquid-free covalent reinforcement of carbon nanotube dry-spun yarns and free-standing sheets

Carbon nanotubes (CNTs) possess exceptional mechanical properties, surpassing stiffness and strength metrics of common materials such as steel alloys by 100× at the nanoscale. However, when myriads of individual CNTs are bundled together into macroscopic ensembles like fibers or sheets, the result is a 100-fold drop in strength compared to its individual components. Here we present a general strategy aimed to close this gap in property scaling. By using vapor-phase polymerization of a crosslinkable polymer, we reinforced the weak interlinkages among individual CNTs within both yarns and sheets to promote a better transference of mechanical load across the structure. After the treatment, dry-spun, low-density 2.3 μm thin yarns increased their elastic moduli by at least 300%, and free-standing CNT sheets exhibited a 10× boost. In-situ synchrotron small-angle X-ray scattering revealed that polymer-reinforced yarns undergo limited CNT bundle rearrangement when subjected to tensile loads compared to pristine yarns. This evidence supports the hypothesis that the polymer hinders CNTs slippage, the root cause of the poor scaling of mechanical properties in these materials. While we demonstrated this reinforcement method for CNT structures, it is not specific to CNTs and could be used in a wide variety of other hierarchical nanostructured ensembles.

Effects of Heat Generation/Absorption on a Stagnation Point Flow Past a Stretching Sheet Carbon Nanotube Water-Based Hybrid Nanofluid with Newtonian Heating

This study investigates the mathematical modelling of heat generation/absorption effect on the convective flow of single wall carbon nanotube-copper (SWCNT-Cu)/water hybrid nanofluid towards a stagnation point past a stretching sheet with Newtonian heating. The set of governing equations in the form of non-linear partial differential equations are first transform using the similarity transformation technique then solved numerically by the Runge-Kutta-Fehlberg (RKF45) method in Maple software. The numerical solutions were obtained for the surface temperature, the heat transfer coefficient and the skin friction coefficient as well as the velocity and the temperature profiles. The features of the flow and heat transfer characteristics for various values of the stretching parameter, the conjugate parameter, the nanoparticle volume fraction parameter and the heat source/sink parameter are analyzed and discussed. It is found that effects of hybrid nanoparticles are more significant for lower stretching parameter and for large conjugate parameter values, as well as the heat generation/absorption.

Directional, Low-Energy Driven Thermal Actuating Bilayer Enabled by Coordinated Submolecular Switching.

The authors reveal a thermal actuating bilayer that undergoes reversible deformation in response to low‐energy thermal stimuli, for example, a few degrees of temperature increase. It is made of an aligned carbon nanotube (CNT) sheet covalently connected to a polymer layer in which dibenzocycloocta‐1,5‐diene (DBCOD) actuating units are oriented parallel to CNTs. Upon exposure to low‐energy thermal stimulation, coordinated submolecular‐level conformational changes of DBCODs result in macroscopic thermal contraction. This unique thermal contraction offers distinct advantages. It's inherently fast, repeatable, low‐energy driven, and medium independent. The covalent interface and reversible nature of the conformational change bestow this bilayer with excellent repeatability, up to at least 70 000 cycles. Unlike conventional CNT bilayer systems, this system can achieve high precision actuation readily and can be scaled down to nanoscale. A new platform made of poly(vinylidene fluoride) (PVDF) in tandem with the bilayer can harvest low‐grade thermal energy and convert it into electricity. The platform produces 86 times greater energy than PVDF alone upon exposure to 6 °C thermal fluctuations above room temperature. This platform provides a pathway to low‐grade thermal energy harvesting. It also enables low‐energy driven thermal artificial robotics, ultrasensitive thermal sensors, and remote controlled near infrared (NIR) driven actuators.

Highly-porous Super-Growth carbon nanotube sheet cathode develops high-power Lithium-Air Batteries

Lithium-Air Battery (LAB) is expected to develop ultra-high energy density batteries, but the low rate performance and poor cycle life of present LAB cells hinder practical development. Here we report that a highly porous carbon nanotube (CNT) cathode dramatically enhances the rate capability of LAB. Single-walled CNTs (SWCNTs) with wavy patterns prepared from the Super-Growth (SG) method successfully provided CNT sheets with high porosity of up to 94%. The pore structure was characterized by two distinct pores in size, namely, highly extended mesoscale (approximately 5–200 nm) pores formed inside CNT bundles that provide large surface area for oxygen reduction reaction (ORR) and inter-bundle gaps in a micrometer scale that works for oxygen diffusion path. This porous CNT sheet cathode significantly increased the discharge rate of LAB cells, specifically enabling a high discharge current density of 3.0 mA/cm2 securing practical cell capacity of 3.3 mAh/cm2, which is comparable to the current LiB technology that provides ∼3 mAh/cm2 cell capacity at ∼1C rate (∼3 mA/cm2) discharge. Furthermore, this highly porous cathode was also effective for extending the cycle life of LAB cells. Such bimodal pore architecture of the CNT sheet cathode paves the new strategy for developing high-power energy-dense LAB.

Facile and low-cost preparation of Co and N co-doped hierarchical porous carbon as a functional separator for Li-S batteries

Despite their ultrahigh theoretical capacity, the practical application of lithium-sulfur batteries (LiSBs) is still severely hindered by the shuttle effect of lithium polysulfides. Herein, we develop a Co and N co-doped carbon (CoN-CNT/HPC) as a modifying separator material to suppress this shuttle effect. The production of the material is low-cost and can be easily scaled up. The as-prepared CoN-CNT/HPC has a hybrid structure consisting of carbon nanotube (CNT) and hierarchical porous carbon sheet (HPC). This structure not only provides efficient pathways for charge transport but also encourages physical adsorption of polysulfides during the lithiation process. Additionally, the Co and N co-doping promotes the chemical adsorption of polysulfides and catalyzes polysulfide conversion. When used as a separator layer in Li-S batteries, CoN-CNT/HPC delivers excellent cycling stability with a low decay rate of 0.04% per cycle over 500 cycles at 2C. Even at high area sulfur loading of 5.5 mg/cm2, the cell using CoN-CNT/HPC separator still exhibits a high initial capacity of 646 mAh/g at 0.5 C and an outstanding cycling stability (561 mAh/g after 100 cycles). The present work provides a simple and effective design strategy of separator materials for high performance Li-S batteries.

Robust Jumping Actuator with a Shrimp-Shell Architecture.

It is highly desirable to develop compact- and robust-film jumping robots that can withstand severe conditions. Besides, the demands for strong actuation force, large bending curvature in a short response time, and good environmental tolerance are significant challenges to the material design. To address these challenges, this paper reports the fabrication of a thin-film jumping actuator, which exhibits a shrimp-shell architecture, from a conjugated ladder polymer (cLP) that is connected by carbon nanotube (CNT) sheets. The hierarchical porous structure ensures the fast absorption and desorption of organic vapor, thereby achieving a high response rate. The actuator does not exhibit shape distortion at temperatures of up to 225°C and in concentrated sulfuric acid, as well as when immersed in many organic solvents. This work avails a new design strategy for high-performance actuators that function under harsh and complicated conditions.

Topographically Conductive Butterfly Wing Substrates for Directed Spiral Ganglion Neuron Growth (Small 38/2021)

Topographically Conductive Materials In article number 2102062, Xiaoyun Qian, Yuanjin Zhao, Renjie Chai, and co-authors construct a composite conductive topological substrate by integrating super-aligned carbon nanotube sheets (SA-CNTs) and methacrylated gelatin (GelMA) hydrogel on Morpho Menelaus butterfly wings. This integrated substrate possesses the anisotropic topology of wing surface and the high conductivity of CNTs, and exhibits great potential to promote the adhesion, growth, orientation, and synapse development of spiral ganglion neurons.

Chlorosulfonic Acid Stretched Carbon Nanotube Sheet for Flexible and Low-Voltage Heating Applications.

The carbon nanotube (CNT) is celebrated for its electrothermal property, which indicates the capability of a material to transform electrical energy into heat due to the Joule effect. The CNT nanostructure itself, as a one-dimensional material, limits the electron conduction path, thereby creating a unique heating phenomenon. In this work, we explore the possible correlation between CNT alignment in sheets and heating performance. The alignment of carbon nanotubes is induced by immersion and stretching in chlorosulfonic acid (CSA) solution. The developed CSA-stretched CNT sheet demonstrated excellent heating performance with a fast response rate of 6.5 °C/s and reached 180 °C in less than 30 s under a low voltage of 2.5 V. The heating profile of the stretched CNT sheet remained stable after bending and twisting movements, making it a suitable heating material for wearable devices, heatable smart windows, and in de-icing or defogging applications. The specific strength and specific conductance of the CSA-stretched CNT sheet also increased five- and two-fold, respectively, in comparison to the pristine CNT sheet.

Topographically Conductive Butterfly Wing Substrates for Directed Spiral Ganglion Neuron Growth.

Spiral ganglion neuron (SGN) degeneration can lead to severe hearing loss, and the directional regeneration of SGNs has shown great potential for improving the efficacy of auditory therapy. Here, a novel 3D conductive microstructure with surface topologies is presented by integrating superaligned carbon-nanotube sheets (SA-CNTs) onto Morpho Menelaus butterfly wings for SGN culture. The parallel groove-like topological structures of M. Menelaus wings induce the cultured cells to grow along the direction of its ridges. The excellent conductivity of SA-CNTs significantly improves the efficiency of cellular information conduction. When integrating the SA-CNTs with M. Menelaus wings, the SA-CNTs are aligned in parallel with the M. Menelaus ridges, which further strengthens the consistency of the surface topography in the composite substrate. The SA-CNTs integrated onto butterfly wings provide powerful physical signals and regulate the behavior of SGNs, including cell survival, adhesion, neurite outgrowth, and synapse formation. These features indicate the possibility of directed regeneration after auditory nerve injury.

Tribological Behavior of Poly(tetrafluoroethylene) and Its Composites Reinforced by Carbon Nanotubes and Graphene Sheets: Molecular Dynamics Simulation

Low‐dimensional fillers play an important role in improving the tribological properties of poly(tetrafluoroethylene) (PTFE) composites. However, the reinforcement mechanism is not fully understood, since few in situ experiments are able to capture the dynamics evolution and interfacial behavior of fillers. Herein, the tribological behavior of PTFE composites filled with graphene (Gr) sheets and carbon nanotubes (CNT) at the nanoscale is investigated. The results demonstrate that the composites filled with the CNT and Gr fillers have much better wear resistance than that of the pure PTFE, and the wear amounts are reduced by 76.2% and 85.7%, respectively. The relative bond and angle energy of PTFE indicate less deformation in the reinforced composite matrices. The calculations of interfacial interaction energy and radial distribution function reveal that the Gr fillers have better reinforcements than CNT due to stronger interactions at the Gr/PTFE interfaces.

Heat treatment of carbon nanotube hybrid material for textile applications

The paper describes the synthesis of carbon nanotube hybrid material and its post-processing treatment such as heat treatment of carbon nanotube (CNT) sheet to improve its properties for in textile applications. The CNT sheet is synthesized using the floating catalyst chemical vapor deposition (FCCVD) method. The floating catalyst method is a continuous process and can produce industrial scale nanotubes in a single step. The lightweight of the CNT material and its flexibility makes it a suitable candidate for textile and wearable applications. The synthesis process and applications of the new hybrid material are discussed along with the customization of the material.

Hierarchical Porous Carbon Nanotube Skeleton Supported Polydimethylsiloxane Composite with Electrical Continuity for High‐Performance Electromagnetic Shielding

AbstractElectromagnetic (EM) shielding materials have attracted significant attention, owing to their widespread potential in preventing EM irradiation in electrical devices and human bodies. In this study, a hierarchical porous carbon nanotube (CNT) skeleton with electrical continuity is presented, which is rapidly fabricated via the facile microwave pyrolysis of CNT‐coated organic templates, for constructing high‐performance EM shielding materials. Furthermore, the CNT skeleton, which comprises countless intertwined CNTs, can be easily designed into various configurations, such as CNT foams and CNT sheets, with varying conductivities and pore densities. In the as‐constructed CNT‐skeleton‐supported polydimethylsiloxane (PDMS)/CNT‐foam composites, the continuity of intertwined CNTs leads to a high conductivity of 271.2 S m−1 at a CNT loading of 2 wt%. Owing to the multiple reflections and reabsorption of the EM waves in the hierarchical porous CNT skeleton with macroporous, microporous, and hollow structures, the PDMS/CNT‐foam composites exhibit a high EM shielding effectiveness (SE) of 43 dB, mainly via absorption. Additionally, the electrical continuity of the CNT skeleton allows the dissipation of heat in the PDMS/CNT‐skeleton.

Smooth surface induced glossy appearance of freestanding multiwall carbon nanotube sheet

Carbon nanotube (CNT) structures reported in the literature often have a black color with low reflectance and matt surface appearance. Only a few papers reported the high reflectance and glossy appearance of the CNT surface on a substrate. To our knowledge, no one has reported the glossy appearance of freestanding CNT. Herein, we have successfully fabricated a freestanding multi-walled CNT sheet with a glossy or mirror-like surface appearance. Raman spectroscopy confirmed that both matt and glossy freestanding CNT sheets have the same chemical composition. We found that the glossy freestanding CNT sheet has a relatively flat surface morphology compared to matt freestanding CNT sheet, as seen in the atomic force microscopy results. We attributed the glossy appearance due to a relatively flat surface morphology of the freestanding CNT sheet.

Reorientation and Flow of Liquid Crystal for a Pressure Sensor Using Carbon Nanotube Sheets

AbstractThe network formation of carbon nanotubes (CNTs) and the viscoelasticity of liquid crystals (LCs) are synergetic properties that enable the formation of composites very sensitive to external pressure. Using a layered structure with nematic LCs and anisotropic networks formed by highly aligned multiwall CNT sheets, the pressure sensor capability of such structure and its piezoresistive response are demonstrated. The application of pressure on the upper substrate is transmitted via LC elastic deformation and flow onto the underlying CNT sheets, improving the electrical conductance. The fabrication process here is relatively facile and versatile as stretched CNT sheets can be easily transferred to any chosen substrate. The sensor response is linear with decrease of 2.42 Ω kPa−1 as the pressure value increases and it is reversible. The sensitivity depends on the thickness of the overlying LC layer and by its relative change, affected by the spacers during force application, but also on the electrical characteristics of the CNTs. The highest sensitivity is obtained with one single CNT sheet and the responsiveness decreases with the increase of number of layers due to the smaller influence of the LC on the contact resistance of the CNT sheets.

Control of anisotropic conduction of carbon nanotube sheets and their use as planar-type thermoelectric conversion materials

ABSTRACT The large anisotropic thermal conduction of a carbon nanotube (CNT) sheet that originates from the in-plane orientation of one-dimensional CNTs is disadvantageous for thermoelectric conversion using the Seebeck effect since the temperature gradient is difficult to maintain in the current flow direction. To control the orientation of the CNTs, polymer particles are introduced as orientation aligners upon sheet formation by vacuum filtration. The thermal conductivities in the in-plane direction decrease as the number of polymer particles in the sheet increases, while that in the through-plane direction increases. Consequently, a greater temperature gradient is observed for the anisotropy-controlled CNT sheet as compared to that detected for the CNT sheet without anisotropy control when a part of the sheet is heated, which results in a higher power density for the planar-type thermoelectric device. These findings are quite useful for the development of flexible and wearable thermoelectric batteries using CNT sheets.

Using ultra-thin interlaminar carbon nanotube sheets to enhance the mechanical and electrical properties of carbon fiber reinforced polymer composites

A major shortcoming of carbon fiber reinforced polymer composites (CFRP) is their interlaminar performance. This study provides an inexpensive and readily scalable solution to this problem by incorporating ultra-thin sheets of carbon nanotubes (CNT) between the plies (laminates) of CFRPs. To this end, dry carbon fiber fabrics are first sandwiched between CNT sheets. The fabrics are then stacked and infused with epoxy to form a CFRP with interlaminar CNT sheets. Contrary to the typical approach where microns-long CNTs are distributed randomly within a CFRP for reinforcement, this study uses ~100 nm thick CNT sheets consisting of aligned and ultra-long (0.3 mm) nanotubes. Despite their negligible weight fraction of only 0.016%, the interlaminar CNT sheets enhanced the CFRP's flexural strength by 49%, interlaminar shear strength by 30%, and mode I fracture toughness by 30%. X-ray micro-tomography revealed that samples with interlaminar CNTs are significantly resistant to delamination and crack propagation. Moreover, the in-plane electrical conductivity of these composites increased commensurate with the weight fraction of CNTs, providing a maximum enhancement of 278% over the reference sample for 0.048 wt% of CNT sheets. This study reveals that for almost no change in weight and thickness, interlaminar CNT sheets can enhance the electrical conductivity and interlaminar performance of CFRPs.

Implantable Biosupercapacitor Inspired by the Cellular Redox System

AbstractThe carbon nanotube (CNT) yarn supercapacitor has high potential for in vivo energy storage because it can be used in aqueous environments and stitched to inner parts of the body, such as blood vessels. The biocompatibility issue for frequently used pseudocapacitive materials, such as metal oxides, is controversial in the human body. Here, we report an implantable CNT yarn supercapacitor inspired by the cellular redox system. In all living cells, nicotinamide adenine dinucleotide (NAD) is a key redox biomolecule responsible for cellular energy transduction to produce adenosine triphosphate (ATP). Based on this redox system, CNT yarn electrodes were fabricated by inserting a twist in CNT sheets with electrochemically deposited NAD and benzoquinone for redox shuttling. Consequently, the NAD/BQ/CNT yarn electrodes exhibited the maximum area capacitance (55.73 mF cm−2) under physiological conditions, such as phosphate‐buffered saline and serum. In addition, the yarn electrodes showed a negligible loss of capacitance after 10 000 repeated charge/discharge cycles and deformation tests (bending/knotting). More importantly, NAD/BQ/CNT yarn electrodes implanted into the abdominal cavity of a rat's skin exhibited the stable in vivo electrical performance of a supercapacitor. Therefore, these findings demonstrate a redox biomolecule‐applied platform for implantable energy storage devices.

A carbon nanotubes based in situ multifunctional power assist system for restoring failed heart function

BackgroundEnd-stage heart failure is a major risk of mortality. The conductive super-aligned carbon nanotubes sheets (SA-CNTs) has been applied to restore the structure and function of injured myocardium through tissue engineering, and developed as efficient cardiac pacing electrodes. However, the interfacial interaction between SA-CNTs and the surface cells is unclear, and it remains challenge to restore the diminished contraction for a seriously damaged heart.ResultsA concept of a multifunctional power assist system (MPS) capable of multipoint pacing and contraction assisting is proposed. This device is designed to work with the host heart and does not contact blood, thus avoiding long-term anticoagulation required in current therapies. Pacing electrode constructed by SA-­CNTs promotes the epithelial-mesenchymal transition and directs the migration of pro-regenerative epicardial cells. Meanwhile, the power assist unit reveals an excellent frequency response to alternating voltage, with natural heart mimicked systolic/diastolic amplitudes. Moreover, this system exhibits an excellent pacing when attached to the surface of a rabbit heart, and presents nice biocompatibility in both in vitro and in vivo evaluation.ConclusionsThis MPS provides a promising non-blood contact strategy to restore in situ the normal blood-pumping function of a failed heart.