Oriented Carbon Nanotubes Research Articles

Combined analytical and numerical modelling of the electrical conductivity of 3D printed carbon nanotube-cementitious nanocomposites

This study explores the electrical properties of 3D-printed carbon nanotube (CNT)-cementitious nanocomposites using a dual modelling approach that integrates micromechanics with finite element (FE) analysis for self-sensing applications. 3D-printed cementitious structures are prone to early crack formation, and incorporating CNTs enhances the material’s electrical conductivity, enabling a built-in health monitoring system. Given the critical impact of CNT dispersion, waviness, and orientation on the electrical conductivity, a theoretical model was developed to incorporate these factors. Experimental tests were conducted to evaluate the material’s conductivity and mechanical performance, and to validate the model. The results show that CNTs align with the printing direction at a 3D-printed layer’s surface, while maintaining isotropic behaviour at the core. Additionally, although the CNTs aggregate, they do not entangle with each other, instead creating conductive networks within the bundles. Moreover, the CNTs are not straight but wavy, which affects the material’s electrical conductivity. Based on the experimental results and the analytical model, a finite element model was developed to predict the conductivity of printed layers, accounting for varying CNT orientations throughout the layer. The results indicate that the model overestimates 3D-printed materials’ conductivity, suggesting that further studies are needed to account for interlayer effects on the measurements.

Microstructural behavior of CNT-PDMS thin-films for multifunctional systems

Heterogeneous ribbed and non-ribbed carbon nanotube (CNT)-PDMS thin-film systems manufactured by large-scale rolling exhibit large-strain and high strain-rate characteristics with favorable surface behaviors, such as superhydrophobicity and drag reduction. However, it is not well understood how the multi-phase microstructure and material properties of non-ribbed thin-films are related to the surface material behavior and fracture. Hence, the objective of this investigation is to characterize the large-strain mechanical behavior and the microstructure of various CNT-PDMS compositions to understand how the CNT loading, agglomeration, distribution, and orientation affect the mechanical behavior and fracture of CNT-PDMS unribbed systems. Non-ribbed thin tensile testing specimens were fabricated for neat PDMS and CNT-PDMS with different weight CNT distributions to understand non-ribbed behavior. The ultimate strain, strength, and global stress–strain behavior were obtained by uniaxial mechanical testing. Scanning electron microscopy (SEM) of the fracture surface was also obtained for each sample to analyze the microstructure and relate the damage mode to the different weight distributions. Based on these experimental measurements and observations, large-strain, hyperelastic and hyper-viscoelastic material models were used to characterize the material behavior. The hyper-viscoelastic material model was shown to provide the most accurate material description of the thin-film behavior of the viscoelastic PDMS with the high-strength CNTs.

Reversible Electrochemical Swelling of Straight Carbon Nanotube Yarns for High-Performance Linear Actuation.

Coiled artificial muscle yarns outperform their straight counterparts in contractile strokes. However, challenges persist in the fabrication complexity and the susceptibility of the coiled yarns to becoming stuck by surrounding objects during contraction and recovery. Additionally, torsional stability remains a concern. In this study, it is reported that straight carbon nanotube (CNT) yarns when driven by a low-voltage electrochemical approach, can achieve a contractile stroke that surpasses even NiTi shape memory alloy fibers. The key lies in the suitable match between a yarn consisting of randomly aligned CNTs and the reversible and substantial electrochemical swelling induced by solvated ions. Wrinkled structures are formed on the surface of the CNT yarn to adapt to the swelling process. This not only assures torsional stability but also enhances the surface area for improved electrode-electrolyte interaction during electrochemical actuation. Remarkably, the CNT artificial muscle yarn generates a contractile stroke of 8.8% and an isometric stress of 7.5 MPa under 2.5 V actuation voltages, demonstrating its potential for applications requiring low energy consumption while maintaining high operational efficiency. This study highlights the crucial impact of CNT orientation on the effectiveness of electrochemically-driven artificial muscles, signaling new possibilities in smart material and biomechanical system development.

(Invited) Analytical Super-Resolution Microscopy Approaches for the Morphological Characterization of Carbon Nanotube Heterogeneity

The ability to determine the shape, size and orientation of fluorescent single-walled carbon nanotubes is critical for a plethora of applications. Yet the heterogeneity of the nanotube samples is often overlooked due to the lack of investigation approaches which may impact the obtained results. Although techniques such as atomic force microscopy (AFM) and transmission electron microscopy (TEM) could be used to this extent, they require heavy instrumentation and analysis, and do not necessarily allow the temporal and in situ characterization of the samples. On the other hand, super resolution microscopy (SRM) approaches can be used to determine the structure of fluorescent nano-objects with high precision while retaining the possibility to perform in situ studies. In particular, analytical SRM approaches are particularly interesting as they rely only on post-processing and do not require any specific optical component.In this context, we study the performances of three analytical SRM approaches for the determination of SWCNT shape, size and orientation. Using correlative microscopy between optical and AFM approaches this study provides an in-depth comparison of the performances of analytical SRM approaches for the morphological characterization of individual SWCNTs.B.P. Lambert et al., in preparation

Programmable Carbon Nanotube Networks: Controlling Optical Properties Through Orientation and Interaction.

The lattice geometry of natural materials and the structural geometry of artificial materials are crucial factors determining their physical properties. Most materials have predetermined geometries that lead to fixed physical characteristics. Here, the demonstration of a carbon nanotube network serves as an example of a system with controllable orientation achieving on-demand optical properties. Such a network allows programming their optical response depending on the orientation of the constituent carbon nanotubes and leads to the switching of its dielectric tensor from isotropic to anisotropic. Furthermore, it also allows for the achievement of wavelength-dispersion for their principal optical axes - a recently discovered phenomenon in van der Waals triclinic crystals. The results originate from two unique carbon nanotubes features: uniaxial anisotropy from the well-defined cylindrical geometry and the intersection interaction among individual carbon nanotubes. The findings demonstrate that shaping the relative orientations of carbon nanotubes or other quasi-one-dimensional materials of cylindrical symmetry within a network paves the way to a universal method for the creation of systems with desired optical properties.

Impact of Aligned Carbon Nanotubes on the Mechanical Properties and Sensing Performance of EVA/CNTs Composites

This study investigated the mechanical and sensing properties of ethylene-vinyl acetate (EVA)/carbon nanotubes (CNTs) composites in both film and fiber forms. The incorporation of aligned CNTs in the composite fibers possess improved mechanical properties and enhanced sensing performance compared to those of composite films with randomly dispersed CNTs. Thermogravimetric analysis revealed promising thermal stability, indicating potential applications for long-term usage. Cyclic tensile testing demonstrated that the fiber samples with better CNT alignment exhibit higher sensitivity, emphasizing the significance of CNT orientation in constructing an efficient conductive network for strain sensing. Considering the contribution of the CNTs orientation along the measuring direction, a model contains modification parameters was proposed, where a master curve was given, revealing the ideal potential of the EVA/CNTs composite fiber with perfectly aligned CNTs. This work provides valuable insights into the influence of CNT alignment on the mechanical and sensing properties of EVA/CNTs composites. The results underscore the importance of optimizing CNT orientation for enhanced sensing performance in various engineering applications.

Growth of 1D Carbon Nanotube@Perovskite Core-Shellvan der Waals Heterostructures through Chemical Vapor Deposition.

Perovskite is an emerging material with immense potential in the field of optoelectronics. 1D perovskite nanowires are crucial building blocks for the development of optoelectronic devices. However, producing perovskite nanowires with high quality and controlled alignment is challenging. In this study, the direct epitaxial growth of perovskite on oriented carbon nanotube (CNT) templates is presented through a chemical vapor deposition method. The deposition process of lead iodide and methylammonium iodide is systematically investigated, and a layer plus island growth mechanism is proposed to interpret the experimental observations. The aligned long CNTs serve as 1D templates and allow the growth of CNT@perovskite core-shell heterostructure with a high aspect ratio to withstand large deformation. The obtained 1D perovskite materials can be easily manipulated and transferred, enabling the facile preparation of microscale flexible devices. For proof of concept, a photodetector based on an individual CNT@methylammonium lead iodide heterostructure is fabricated. This work provides a new approach to prepare 1D hetero-nanostructure and may inspire the design of novel flexible nanophotodetectors.

Performance of Particle Swarm Optimization in Predicting the Orientation of π-Conjugated Molecules Inside Carbon Nanotubes Compared with Density Functional Theory Calculations.

Particle swarm optimization (PSO) was employed to obtain the global minimum of host-guest structures consisting of a triiodobenzene molecule (BzI3) inside an armchair (m,m) nanotube (BzI3@(m,m)), whose host-guest interactions are approximated by Lennard-Jones (LJ) potentials. The host-guest structures obtained using the PSO-LJ method were then compared with those obtained through dispersion-corrected density functional theory (DFT) calculations to evaluate the performance of the PSO-LJ approach in predicting the guest orientation inside a tube. When the inner space of the host tube is limited for guest encapsulation, the PSO-LJ method can reproduce the DFT results of BzI3@(m,m) in terms of the guest orientation. Conversely, in nanotubes with a sufficiently large space to allow a guest to freely move, corresponding to weak tube confinement, the PSO-LJ method yields guest orientations that are different from those obtained through DFT calculations; however, both methods obtain energetically close guest orientations. Accordingly, PSO-LJ method-assisted DFT calculations can quickly provide energetically stable guest orientations in BzI3@(m,m) in weak tube confinement, which can be ignored in DFT calculations, where a single initial geometry is typically used.

Wet-spinning of carbon nanotube fibers: dispersion, processing and properties

ABSTRACT Owing to the intrinsic excellent mechanical, electrical, and thermal properties of carbon nanotubes (CNTs), carbon nanotube fibers (CNTFs) have been expected to become promising candidates for the next-generation of high-performance fibers. They have received considerable interest for cutting-edge applications, such as ultra-light electric wire, aerospace craft, military equipment, and space elevators. Wet-spinning is a broadly utilized commercial technique for high-performance fiber manufacturing. Thus, compared with array spinning from drawable CNTs vertical array and direct dry spinning from floating catalyst chemical vapor deposition (FCCVD), the wet-spinning technique is considered to be a promising strategy to realize the production of CNTFs on a large scale. In this tutorial review, we begin with a summative description of CNTFs wet-spinning process. Then, we discuss the high-concentration CNTs wet-spinning dope preparation strategies and corresponding non-covalent adsorption/charge transfer mechanisms. The filament solidification during the coagulation process is another critical procedure for determining the configurations and properties for derived CNTFs. Next, we discuss post-treatment, including continuous drafting and thermal annealing, to further optimize the CNTs orientation and compact configuration. Finally, we summarize the physical property-structure relationship to give insights for further performance promotion in order to satisfy the prerequisite for detailed application. Insights into propelling high-performance CNTFs production from lab-scale to industry-scale are proposed, in anticipation of this novel fiber having an impact on our lives in the near future.

A subbands study on the resistivity of field-effect CNT-based piezoresistive nanocomposites

In this paper, an analytical model based on the percolation theory has been developed to predict the subbands effect on the effective electrical resistivity of carbon nanotubes (CNT)-based polymer nanocomposites. The CNTs are considered as randomly distributed or aligned channel material in the polymer transmitting electrons through tunneling. The tunneling effect takes into account the electron transmission between each connected pair of CNTs to evaluate electrical resistivity. The modeling approach contains two steps of primary prediction of resistivity and further calculation of CNTs’ displacements and subsequent change of the resistance. A good agreement is found between the analytical model predictions and experimental data when the tunneling behavior was considered in the percolation transition region. The effect of CNT diameter, orientation state, and subbands on the resistivity has been investigated. The results depict that subbands increment is a collateral benefit to the aspect ratio in decreasing the resistivity. The analytical results demonstrate that a random CNT dispersion leads to a decreased piezoresistivity, while an increased strain range depicts a more non-linear behavior.

Strengthening sandwich composites by laminating ultra-thin oriented carbon nanotube sheets at the skin/core interface

Strong, tough, and lightweight composites are increasingly needed for diverse applications, from wind turbines to cars and aircraft. These composites typically contain sheets of strong and high-modulus fibers in a matrix that are joined with other materials to resist fracture. Coupling these dissimilar materials together is challenging to enhance delamination properties at their interface. We herein investigate using a trace amount of carbon nanotube sheets to improve the coupling between composite skins and core in a composite sandwich. Ultra-thin (∼100 nm) forest-drawn multi-walled carbon nanotube (MWNT) sheets are interleaved within the skin/core interphase, with MWNTs aligned in the longitudinal direction. The mechanical behavior is characterized by end-notched flexural testing (ENF). With two MWNT sheets placed in the skin/core interphase, the following performance enhancements are achieved: 36.8 % increase in flexural strength; 127.3 % and 125.7 % increases in mode I & II fracture toughness values, respectively; and 152.8 % increase in interfacial shear strength (IFSS). These are achieved with negligible weight gain of the composite sandwich (0.084 wt% increase over the baseline sandwich without MWNT sheets). The finite element simulation results show that MWNT sheets enhance the skin/core coupling by reducing stress concentration, enabling the transition from catastrophic brittle failure to a stable ductile failure mode. The MWNT sheets interleaved sandwich composites are thus demonstrated to be stronger and tougher while providing electrical conductivity (4.3 × 104S/m) at the skin/core interface for potential de-icing, electromagnetic interference shielding, and structural health monitoring.

Preparation and performance of biaxially stretched CNT-SBS/POE flexible strain sensor with a double percolation structure

Wearable flexible strain sensors have prospective application prospects in human motion monitoring, human-computer interaction, and information transmission. However, facilely manufacturing flexible strain sensors with a high sensitivity and extended sensing range remains challenging. Herein, a flexible strain sensor with a double percolation structure was prepared through simple melting mixing and biaxial stretching. To this end, carbon nanotubes (CNTs) filled styrene butadiene styrene (SBS) and polyolefin elastomer (POE) were employed as the conductive and insulating phases, respectively. The effects of biaxial stretching on sensor performance were systematically studied. During biaxial stretching, the as-obtained CNT-SBS/POE nanocomposites with double percolation structure exhibited better processing performance and stability than conventional CNT-SBS binary composites. Biaxial stretching results in better dispersion and planar orientation of CNTs in polymers, improving the sensing property of strain sensors. The optimized stretching ratio of double percolation structured composites was determined as 1.5, with 3 wt% CNT-SBS/POE sensor exhibiting high sensitivity (gauge factor = 7501.69) over a wide strain monitoring range (0–300% strain). Additionally, the flexible strain sensors could monitor physiological activities and information transmission with good reliability, thereby promising for human-machine interaction, wearable, and medical monitoring.

On the roles of strain gradient tensors in quasi‐3D nonlinear dynamics of microplate‐type piezoelectric systems of energy harvesting under triangular mechanical actuation

AbstractThe small‐scale‐dependent nonlinear dynamical attributes of microplate‐type laminated piezoelectric systems of harvesting energy subjected to a triangular mechanical actuation are explored in the current exploration. The core of harvesting systems is supposed to be made of nanocomposites reinforced by randomly oriented carbon nanotubes (CNTs) having various degrees of agglomeration coated by piezoelectric layers. In this regard, the microplate‐type systems of harvesting energy are modeled via a quasi‐3D plate theory combined with the modified strain gradient elasticity in the presence of various microsize‐dependent strain gradient tensors. Thereafter, the solution of the developed coupled electromechanical size‐dependent nonlinear problem is obtained numerically by utilizing the meshless collocation approach employing incorporation of the polynomial and radial basis functions to remove any feasible singularity for the associated moment matrices. It comes to the conclusion that by elevating the quantity of CNTs disclosed within the clusters, the significance of the microsize dependency in the achieved voltage enhances from 22.06% to 22.73% toward the simply supported bridge‐type context, and from 33.00% to 33.92% toward the clamped bridge‐type context.Highlights Development of a microstructural‐dependent quasi‐3D shear flexible energy harvester model. Incorporating the roles of various strain gradient tensors in the nonlinear dynamics of microharvesters. Size‐dependent time‐histories of achieved voltage from triangular mechanical‐loaded microharvesters. Influence of the CNT reinforcement clustering on the nonlinear dynamic performance.

Features of electron reflection by layer of carbon nanotubes

The anisotropic properties of a layer of carbon nanotubes upon electron reflection have been studied. Only a small part of the incident electrons is found to reflect from a target with a surface layer of oriented carbon nanotubes. Reflection occurs only from a layer of horizontally oriented nanotubes at an angle of incidence greater than 80° and vertically oriented nanotubes at an angle of incidence less than 10°. The effect is explained by peculiarities of the formation of an electron flux in the surface layers of the target.

Ku-Band Mixers Based on Random-Oriented Carbon Nanotube Films.

Carbon nanotubes (CNTs) are a type of nanomaterial that have excellent electrical properties such as high carrier mobility, high saturation velocity, and small inherent capacitance, showing great promise in radio frequency (RF) applications. Decades of development have been made mainly on cut-off frequency and amplification; however, frequency conversion for RF transceivers, such as CNT-based mixers, has been rarely reported. In this work, based on randomly oriented carbon nanotube films, we focused on exploring the frequency conversion capability of CNT-based RF mixers. CNT-based RF transistors were designed and fabricated with a gate length of 50 nm and gate width of 100 μm to obtain nearly 30 mA of total current and 34 mS of transconductance. The Champion RF transistor has demonstrated cut-off frequencies of 78 GHz and 60 GHz for fT and fmax, respectively. CNT-based mixers achieve high conversion gain from -11.4 dB to -17.5 dB at 10 to 15 GHz in the X and Ku bands. Additionally, linearity is achieved with an input third intercept (IIP3) of 18 dBm. It is worth noting that the results from this work have no matching technology or tuning instrument assistance, which lay the foundations for the application of Ku band transceivers integrated with CNT amplifiers.

Predicting mechanical properties of 3D printed nanocomposites using multi-scale modeling

The main objective of this research is to predict the Young’s modulus of 3D-printed specimens made of nanocomposites. Printable nanocomposites filaments reinforced with various portions of carbon nanotubes (CNTs) are produced at the first stage. At the second stage, extruded nanocomposite filaments are fed into a 3D desktop printer and tensile specimens are printed with two different infill patterns. A multi-scale modeling is developed as a hierarchical computational procedure covering involved scales of micro, meso and macro. Treating CNT length, orientation and agglomeration as random parameters, stochastic modeling is performed. CNT length is considered at microscale, while CNT agglomeration and orientation are taken into account at the scale of meso. The infill patterns and printing parameters are captured at the uppermost scale of macro. The Young’s modulus of both nanocomposite filaments and 3D printed samples are predicted and compared with the results of experimental characterization.

Enhancing interfacial shear strength with tailored carbon nanotube orientations: A micromechanical hierarchical model of single fiber fragmentation tests

This study explores the effects of carbon nanotube (CNT) orientation on stress transfer in carbon fiber (CF) composites using the Single Fiber Fragmentation Test (SFFT). A micromechanical hierarchical model, utilizing the Finite Element Method (FEM), is developed to analyze a CF composite with a CNT-reinforced interfacial region, encapsulated within an epoxy resin matrix. The Mori-Tanaka method is utilized to calculate the effective properties of the CNT-reinforced interfacial region of the CF, taking into account different CNT orientations and volume fractions. Scenarios involving radial, longitudinal, and random CNT orientations are considered. Moreover, the study also incorporates the nonlinear plastic behavior of the epoxy matrix. A novel analytical framework that leverages FEM to compute variables such as critical length, interfacial shear strength (IFSS), and average normal stress is proposed to accomplish it. Numerical results are compared to existing experimental data for validation. For the validation of the proposed methodology, experimental data available in the literature were used. The model predictions show that specific orientations and volume fractions of CNTs have the potential to enhance IFSS. However, the enhancement in the elastic stiffness of the interfacial region, attributed to the inclusion of CNTs, does not entirely explain the improvements in IFSS observed in the experimental studies from the literature.

Controlled synthesis, properties, and applications of ultralong carbon nanotubes.

Carbon nanotubes (CNTs) are typical one-dimensional nanomaterials which have been widely studied for more than three decades since 1991 because of their excellent mechanical, electrical, thermal, and optical properties. Among various types of CNTs, the ultralong CNTs which have lengths over centimeters and defect-free structures exhibit superior advantages for fabricating superstrong CNT fibers, CNT-based chips, transparent conductive films, and high-performance cables. The length, orientation, alignment, defects, cleanliness, and other microscopic characteristics of CNTs have significant impacts on their fundamental physical properties. Therefore, the controlled synthesis and mass production of high-quality ultralong CNTs is the key to fully exploiting their extraordinary properties. Despite significant progress made in the study of ultralong CNTs during the past three decades, the precise structural control and mass production of ultralong CNTs remain a great challenge. In this review, we systematically summarize the growth mechanism and controlled synthesis strategies of ultralong CNTs. We also introduce the progress in the applications of ultralong CNTs. Additionally, we summarize the scientific and technological challenges facing the mass production of ultralong CNTs and provide an outlook and in-depth discussion on the future development direction.

Random distribution of interphase characteristics on the overall electro-mechanical properties of CNT piezo nanocomposite: Micromechanical modeling and Monte Carlo simulation

A phenomenological study is carried out to speculate the statistical impacts of the CNT/polymer interphase on the overall electro-elastic behavior of piezo-polymer nanocomposites by presenting a full-field micromechanical model. The nanocomposite system consists of carbon nanotube (CNT) and PVDF. Various statistical distributions, including Weibull, log-normal, normal, beta, and uniform distributions on the thickness and strength of the interphase are carefully assessed. The results are compared with experimental data, and satisfactory agreements are reported. It is found that, compared to the random distribution of the interphase strength, the statistical distribution of the interphase thickness has more effect on the overall electro-elastic properties. For example, for the effective longitudinal modulus, the overall coefficients of variation are 14 %, 13 %, 13.56, and 10 %, respectively, for the normal, Weibull, beta, and uniform distributions of the thickness compared with the measured experimental values. Also, the effects of the CNT content, aspect ratio, and orientation on the effective electro-elastic properties by considering the various random distributions are fully examined. Moreover, using the Monte Carlo simulation, the probability of not meeting design specification (failure probability) is evaluated at the random distributions of the interphase strength and thickness to identify the optimum CNT content for which the values of the overall properties are maximum. It is obtained that the failure probabilities are different for 5–8 % CNT volume fraction in the distributions of the thickness, and for only 5 VF% CNT in the strength distributions. For other values of the CNT content, the failure probabilities are independent of the distribution of the interphase strength and thickness.

Vibration characteristics of composite damping plate with randomly oriented carbon nanotube reinforced stiffeners

Vibration characteristics of composite damping plate with randomly oriented carbon nanotube reinforced stiffeners