Collapsed Carbon Nanotubes Research Articles

Self-Locking in Collapsed Carbon Nanotube Stacks via Molecular Dynamics

Self-locking structures are often studied in macroscopic energy absorbers, but the concept of self-locking can also be effectively applied at the nanoscale. In particular, we can engineer self-locking mechanisms at the molecular level through careful shape selection or chemical functionalisation. The present work focuses on the use of collapsed carbon nanotubes (CNTs) as self-locking elements. We start by inserting a thin CNT into each of the two lobes of a collapsed larger CNT. We aim to create a system that utilises the unique properties of CNTs to achieve stable configurations and enhanced energy absorption capabilities at the nanoscale. We used molecular dynamics simulations to investigate the mechanical properties of periodic systems realised with such units. This approach extends the application of self-locking mechanisms and opens up new possibilities for the development of advanced materials and devices.

Bouligand-like structured CNT film with tunable impact performance through pitch angle and intertube interaction

The Bouligand structure, characterized by a helicoidal arrangement of fibers, is prevalent in arthropods. Leveraging the exceptional impact resistance inherent in this structure, mantis shrimp could effortlessly crack the shells of shellfish using their dactyl club. Drawing inspiration from this natural phenomenon, we propose a novel Bouligand-like structured carbon nanotube film (BCNF) that combines the Bouligand structure with super-strong one-dimensional carbon nanotubes (CNTs). Through systematic investigation via molecular dynamics simulations, we explore the impact resistance and energy dissipation properties of BCNF. Our results reveal that the impact behaviors under different velocities can be tuned by adjusting the pitch angle of BCNFs. At an impact velocity of 1 km/s, the projectile exhibits three typical phenomena after impact, including embedding in the film, bouncing back, and penetration. At an impact velocity of 2 km/s, all films are penetrated. Furthermore, to enhance the impact resistance of BCNF, we introduce intertube crosslinking bonds, forming a crosslinked Bouligand-like structured CNT film (CBCNF). The study demonstrates that crosslinking effectively modulates the energy dissipation mode of the film. With increasing crosslinking density, the predominant energy dissipation mode shifts from interface sliding and bending of the CNTs to the fracture and collapse of CNTs. This research provides valuable insights into the microstructure design of CNT-based films and offers theoretical guidance for their applications in impact protection.

Dual-Ion Co-Regulation System Enabling High-Performance Electrochemical Artificial Yarn Muscles with Energy-Free Catch States

HighlightsThe dual-ion co-regulation system shortens ion migration pathways, which endow the yarn muscle with high contractile stroke (34.7%) and contractile rate (9.4% s−1), more than twice that of the “rocking-chair” -type ion migration yarn muscles.The yarn muscle shows high isometric stress of 18.4 MPa (61 times that of skeletal muscles) and 8 times the isometric stress of the “rocking-chair” -type yarn muscles at a higher frequency.The intercalation reaction between {text{PF}}_{6}^{ - }and collapsed carbon nanotubes allows the yarn muscle to achieve an energy-free high-tension catch state

Free Vibration Analysis of Thin-Walled Beams Using Two-Phase Local–Nonlocal Constitutive Model

Abstract A mathematical model is developed based on the thin-walled beams theory for free vibration analysis of nano/micro scale beams having nonlocal properties and arbitrary cross sections. Constitutive relations are defined by using two-phase local–nonlocal constitutive formulation. Equations of motion are derived by use of Hamilton‘s principle. Both the local and nonlocal part of the model is solved by the displacement-based finite element method. Numerical results are obtained and examined for nonlocal box beams and collapsed carbon nanotubes. In general, it is observed that the natural frequency decreases by increasing the nonlocal parameter or the volume fraction of the nonlocal part.

Universality of moiré physics in collapsed chiral carbon nanotubes

We report the existence of moiré patterns and magic angle physics in all families of chiral collapsed carbon nanotubes. A detailed study of the electronic structure of all types of chiral nanotubes, previously collapsed via molecular dynamics, has been performed. We find that each family possesses a unique geometry and moiré disposition, as well as a characteristic number of flat bands. Remarkably, all kinds of nanotubes behave the same with respect to magic angle tuning, showing a monotonic behavior that gives rise to magic angles in full agreement with those of twisted bilayer graphene. Therefore, magic angle behavior is universally found in chiral collapsed nanotubes with a small chiral angle, giving rise to moiré patterns. Our approach comprises first-principles and semi-empirical calculations of the band structure, density of states and spatial distribution of the localized states signaled by flat bands.

Tailoring Dense, Orientation-Tunable, and Interleavedly Structured Carbon-Based Heat Dissipation Plates.

The controllability of the microstructure of a compressed hierarchical building block is essential for optimizing a variety of performance parameters, such as thermal management. However, owing to the strong orientation effect during compression molding, optimizing the alignment of materials perpendicular to the direction of pressure is challenging. Herein, to illustrate the effect of the ordered microstructure on heat dissipation, thermally conductive carbon-based materials are fabricated by tailoring dense, orientation-tunable, and interleaved structures. Vertically aligned carbon nanotube arrays (VACNTs) interconnected with graphene films (GF) are prepared as a 3D core-ordered material to fabricate compressed building blocks of O-VA-GF and S-VA-GF. Leveraging the densified interleaved structure offered by VACNTs, the hierarchical O-VA-GF achieves excellent through-plane (41.7W m-1 K-1 ) and in-plane (397.9W m-1 K-1 ) thermal conductivities, outperforming similar composites of S-VA-GF (through-plane: 10.3W m-1 K-1 and in-plane: 240.9W m-1 K-1 ) with horizontally collapsed carbon nanotubes. As heat dissipation plates, these orderly assembled composites yield a 144% and 44% enhancement in the cooling coefficient compared with conventional Si3 N4 for cooling high-power light-emitting diode chips.

Stepwise Artificial Yarn Muscles with Energy-Free Catch States Driven by Aluminum-Ion Insertion.

Present artificial muscles have been suffering from poor actuation step precision and the need of energy input to maintain actuated states due to weak interactions between guest and host materials or the unstable structural changes. Herein, these challenges are addressed by deploying a mechanism of reversible faradaic insertion and extraction reactions between tetrachloroaluminate ions and collapsed carbon nanotubes. This mechanism allows tetrachloroaluminate ions as a strong but dynamic "locker" to achieve an energy-free high-tension catch state and programmable stepwise actuation in the yarn muscle. When powered off, the muscle nearly 100% maintained any achieved contractile strokes even under loads up to 96,000 times the muscle weight. The actuation mechanism allowed the programmable control of stroke steps down to 1% during reversible actuation. The isometric stress generated by the yarn muscle (14.6 MPa in maximum, 40 times that of skeletal muscles) was also energy freely lockable and step controllable with high precision. Importantly, when fully charged, the muscle stored energy with a high capacity of 102 mAh g-1, allowing the muscle as a battery to power secondary muscles or other devices.

Role of nanotube chirality on the mechanical characteristics of pillared graphene

Pillared graphene composed of carbon nanotubes (CNTs) and graphene sheets shows a host of robust properties with diverse applications. Herein, mechanical characteristics of pillared graphene composed of six different chiral CNTs are explored using molecular dynamic (MD) simulations. Pillared graphene shows distinct tensile and compression mechanical characteristics that are greatly dictated by the chirality of CNT pillars. Subjected to planar and CNT-axial directional loads, (6,6) and (8,4) chiral CNTs-dominated pillared graphene are the most mechanically robust structures in terms of tensile strength. Upon compression, four distinct loading stages, including elastic compression, progressive compression, collapse of CNTs and densification, can be identified from their loading curves and re-alignment analysis of CNTs. Besides wrinkling of graphene, compression-induced structural transformations are quantitatively explained by inclination of CNTs in pillared graphene. As a result of de-wrinkling/wrinkling behaviors of graphene sheets, specific pillared graphene structures yield negative Poisson's ratio. Analysis of compression energy-absorption indicators such as crush force efficiency, stroke efficiency and specific energy-absorption reveal that they are good energy-absorbers, with the highest performance of energy-absorption for (7,5) CNT-dominated pillared graphene. The study provides critical understanding of role of CNT chirality on the mechanical properties of pillared graphene for optimal design of high-dimensional hybrid CNT-graphene structures with high mechanical performance.

Identification of Collapsed Carbon Nanotubes in High-Strength Fibers Spun from Compositionally Polydisperse Aerogels

Carbon Nanotubes (CNTs) of sufficiently large diameter and a few layers self-collapse into flat ribbons at atmospheric pressure, forming bundles of stacked CNTs that maximize packing and thus CNT interaction. Their improved stress transfer by shear makes collapsed CNTs ideal building blocks in macroscopic fibers of CNTs with high-performance longitudinal properties, particularly high tensile properties as reinforcing fibres. This work introduces cross-sectional transmission electron microscopy of FIB-milled samples as a way to univocally identify collapsed CNTs and to determine the full population of different CNTs in macroscopic fibers produced by spinning from floating catalyst chemical vapour deposition. We show that close proximity in bundles is a major driver for collapse and that CNT stoutness (number of layers/diameter), which dominates the collapse onset, is controlled by the growth promotor. Despite differences in decomposition route, different C precursors lead to similar distributions of the ratio layers/diameter. The synthesis conditions in this study give a maximum fraction of collapsed CNTs of 70$\%$ when using selenium as promotor, corresponding to an average of $0.25 layer/nm$.

Ab initio predictions of graphite-like phase with anomalous grain boundaries and flexoelectricity from collapsed carbon nanotubes.

Although large-radius carbon nanotubes (CNTs) are now available in macroscopic quantities, little is known about their condensed phase. Large-scale density functional theory calculations predict a low energy phase in which the same-diameter "dog-bone" collapsed CNTs form a graphite-like phase with complex, anomalous grain boundaries (GBs). The excess GB volume does not prevent the strong van der Waals coupling of the flattened CNT sides into AB stacking. The associated GB energetics is dominated by the van der Waals energy penalty and high curvature bending of the loop CNT edges, which exhibit reactivity and flexoelectricity. The large density and superior mechanical rigidity of the proposed microstructural organization as well as the GB flexoelectricity are desirable properties for developing ultra-strong composites based on large-radius CNTs.

Macroscopic yarns of FeCl3-intercalated collapsed carbon nanotubes with high doping and stability

Macroscopic arrays of highly-crystalline nanocarbons offer the possibility of modifying the electronic structure of their low dimensional constituents, for example through doping, and studying the resulting collective bulk behaviour. Insertion of electron donors or acceptors between graphitic layers is an attractive method to reversibly increase charge carrier concentration without disruption of the sp2-conjugated system. This work demonstrates FeCl3 intercalation into fibres made up of collapsed (flattened) carbon nanotubes. The bundles of collapsed CNTs, similar to crystallites of graphitic nanoribbons, host elongated layered FeCl3 crystals of hundreds of nm long, much longer than previous reports on graphitic materials and directly observable by transmission electron microscopy and X-ray diffraction. Intercalated CNT fibres remain stable after months of exposure to ambient conditions, partly due to the spontaneous formation of passivating monolayers of FeClO at the crystal edge, preventing both desorption of intercalant and further hydrolysis. Raman spectroscopy shows substantial electron transfer from the CNTs to FeCl3, a well-known acceptor, as observed by G band upshifts as large as 25 cm−1. After resolving Raman features for the inner and outer layers of the collapsed CNTs, strain and dynamic effect contributions of charge transfer to the Raman upshift could be decoupled, giving a Fermi level downshift of −0.72 eV and a large average free carrier concentration of 5.3·1013 cm−2 (0.014 electrons per carbon atom) in the intercalated system. Four-probe resistivity measurements show an increase in conductivity by a factor of six upon intercalation.

One-Dimensional Moiré Superlattices and Flat Bands in Collapsed Chiral Carbon Nanotubes.

We demonstrate that one-dimensional moiré patterns, analogous to those found in twisted bilayer graphene, can arise in collapsed chiral carbon nanotubes. Resorting to a combination of approaches, namely, molecular dynamics to obtain the relaxed geometries and tight-binding calculations validated against ab initio modeling, we find that magic angle physics occur in collapsed carbon nanotubes. Velocity reduction, flat bands, and localization in AA regions with diminishing moiré angle are revealed, showing a magic angle close to 1°. From the spatial extension of the AA regions and the width of the flat bands, we estimate that many-body interactions in these systems are stronger than in twisted bilayer graphene. Chiral collapsed carbon nanotubes stand out as promising candidates to explore many-body effects and superconductivity in low dimensions, emerging as the one-dimensional analogues of twisted bilayer graphene.

Stacking- and chirality-dependent collapse of single-walled carbon nanotubes: A large-scale density-functional study

Using density functional theory with van der Waals (vdW) corrections, we study the collapse of free-standing single-walled carbon nanotubes (also called ``dogbone'' nanotubes). Their thermodynamic stability is strongly influenced by the initial stacking sequence, with lateral shear allowing registry change with turbostratic stacking predominant. The electronic structure of collapsed zigzag and armchair carbon nanotubes is investigated, demonstrating sensitivity to the lattice registry. The opening of small (meV) band gaps is shown for both armchair and zigzag collapsed nanotubes, arising from quantum confinement and charge transfer between the bilayer graphenelike central region and nanotubelike edges. Different scaling rules for the band gaps of collapsed carbon nanotubes are obtained as a function of their widths taking stacking and chirality into account. We reconcile a complete understanding of electronic properties in these deformed tubes with literature theoretical and experimental results, suggesting collapsed nanotubes can be promising candidates as conductive nanoribbons in electronic and spintronic device applications.

Advance in Close-Edged Graphene Nanoribbon: Property Investigation and Structure Fabrication.

The absence of dangling bonds in close-edged graphene nanoribbons (CEGNRs) confers upon them a series of fascinating properties, especially when compared with cylindrical carbon nanotubes and open-edged GNRs. Here, the configuration of CEGNRs is described, followed by the structure-related properties, including mechanical, thermal, electrical, optical, and magnetic properties. Based on the unique structures and extraordinary properties, their potential applications in a variety of fields, such as field-effect transistors, energy suppliers, nanoactuators, and fibers, are discussed. Remarkably, the strategies applied for generating CEGNRs, mainly from the collapse of carbon nanotubes and graphene tubes, are depicted in detail. Finally, the prospects in the research area of CEGNRs are proposed.

Collapsed carbon nanotubes: From nano to mesoscale via density functional theory-based tight-binding objective molecular modeling

Due to the inherent spatial and temporal limitations of atomistic modeling and the lack of efficient mesoscopic models, mesoscale simulation methods for guiding the development of super strong lightweight material systems comprising collapsed carbon nanotubes (CNTs) are currently missing. Here we establish a path for deriving ultra-coarse-grained mesoscopic distinct element method (mDEM) models directly from the quantum mechanical representation of a collapsed CNT. Atomistic calculations based on density functional-based tight-binding (DFTB) extended with Lennard-Jones interactions allow for the identification of the cross-section and elastic constants of an elastic beam idealization of a collapsed CNT. Application of the DFTB quantum treatment is possible due to the simplification in the number of atoms introduced by accounting for the helical and angular symmetries exhibited by twisted and bent CNTs. The multiscale modeling chain established here is suitable for deriving ultra-coarse-grained mesoscopic models for a variety of microscopic filaments presenting complex interatomic bondings.

Smooth sliding and superlubricity in the nanofriction of collapsed carbon nanotubes

We present the characteristics of the sliding friction in large-diameter collapsed carbon nanotubes (CNTs) as emerged from molecular dynamics simulations. The friction force is found to depend strongly on the CNT sliding velocity, the interface contact area, interface commensuration, and temperature. The non-classical smooth sliding and superlubric behaviors identified at the molecular level give a useful starting reference to the ongoing efforts aimed at engineering the mechanical load transfer in material systems comprising collapsed CNTs.

Collapsed carbon nanotubes as building blocks for high-performance thermal materials

The influence of collapsed shape on the thermal transport of carbon nanotubes is studied by nonequilibrium molecular dynamics. Nanotubes of different lengths, diameters, chiralities, and degrees of twist are simulated in the regime in which the thermal transport extends from ballistic to diffusive. In contrast with graphene nanoribbons, which are known to exhibit substantial rough-edge and cross-plain phonon scatterings, the collapsed tubes preserve the quasiballistic phononic transport encountered in cylindrical nanotubes. Stacked-collapsed nanotube architectures, closely related with the strain-induced aligned tubes occurring in stretched nanotube sheets, are shown to inherit the ultrahigh thermal conductivities of individual tubes, and are therefore proposed to form highways for efficient heat transport in lightweight composite materials.

Optical Absorption in Collapsed Carbon Nanotubes

The optical absorption spectra are calculated in collapsed carbon nanotubes, described by dynamical conductivity σyy(ω) for the polarization of electric field parallel to the axis, and \(\tilde{\sigma }_{xx}^{\| }(\omega )\) and \(\tilde{\sigma }_{xx}^{ \bot }(\omega )\) perpendicular to the axis and parallel and perpendicular, respectively, to the flattened region. For σyy(ω), clear interband peaks appear corresponding to band gaps between allowed bands. Inter-wall interaction due to collapsing causes splitting and shift of the peaks from uncollapsed tubes. Such effects are largest in nonchiral zigzag and armchair tubes, for which the spectra depends on the relative displacement in the flattened region, and rapidly decrease for tubes with chiral structure. Depolarization effect suppresses interband absorption in \(\tilde{\sigma }_{xx}^{\| }(\omega )\) and \(\tilde{\sigma }_{xx}^{ \bot }(\omega )\). For \(\tilde{\sigma }_{xx}^{ \bot }(\omega )\), the rapid spatial variation of the effective electric field...

Magnetic Susceptibility of Collapsed Carbon Nanotubes

The orbital magnetic susceptibility is calculated in collapsed carbon nanotubes within an effective-mass scheme for two magnetic-field configurations, perpendicular and parallel to the flattened plane. The response is diamagnetic in both directions and is much larger for the perpendicular configuration, with some rare exceptions. In chiral nanotubes, calculated results show small and almost negligible effects of collapsing except for some modification due to change in the effective magnetic field. In nonchiral zigzag and armchair nanotubes, the susceptibility is strongly modified, depending on relative displacement of two layers in the flattened region.

Spinel Decorated Aligned Carbon Nanotube Arrays As Supercapacitor Electrodes

Accompanying the need for green energy generation is a need for energy storage systems since most green energy sources like solar and wind are intermittent. In recent times, much research focus has been placed on providing more durable and higher capacity energy storage devices like supercapacitors, which has led to the design of better electrode materials for these supercapacitors. Graphitic carbon nanotubes have been tipped as superior materials for making supercapacitors because of their unique electrical properties and pore structure. They are inert, lightweight, have high electrical conductivity, high thermal stability and very high surface areas especially when aligned. As a result, they are very suitable as electrode templates because thin nanosheets or nanoparticles can be embedded within them in a high surface area configuration without excessively sacrificing ion accessibility and electrical conductivity. We report the use of aligned carbon nanotubes as supercapacitor electrode templates and highlight their superiority, as a result of a better ordered pore structure, to entangled or collapsed carbon nanotubes for electrode applications. Specifically, we use Ni-Co mixed oxide and Co-Mn mixed oxide spinels characterized using EDX and XRD as electroactive materials. These spinels have been chosen because of their relatively high electrical conductivity and are optimized for relative metal ratios. Different methods of electrochemical deposition were also explored to achieve uniform coating. However, one challenge associated with using aligned carbon nanotube templates is the resistance between the current collector and the nanotubes. It is well known that an insulating alumina layer is necessary for the sustained and efficient growth of self-aligned nanotubes. In trying to overcome this challenge, we added a molybdenum layer to reduce the resistive effect of the alumina layer. Another challenge is the capillarity induced collapse of the nanotube forest between electrodeposition and annealing during the preparation of the electrode. Our approach to solving this involved the use of a new universally applicable method: specifically supercritical drying to preserve pore structure and prevent forest collapse during annealing after electrodeposition on self-aligned carbon nanotube forests. We highlight the effects each of these processes on the eventual capacitive performance of the prepared electrodes.