Single Carbon Nanotubes Research Articles

Simulation of Cattaneo–Christov heat flux on the flow of single and multi-walled carbon nanotubes between two stretchable coaxial rotating disks

With an objective to unfold the flow and heat transfer characteristics of carbon nanotubes between two stretchable coaxial rotating disks, the present investigation has been carried out. The behavior of single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs) taking water as the base fluid is analyzed. To formulate the energy equation, we have incorporated Cattaneo–Christov heat flux model. Consideration of such kind of model accounts the contribution by thermal relaxation. von Karman transformation has been implemented in order to reconstruct the governing partial differential equations into a system of ordinary differential equations. Employing optimal homotopy analysis method series solutions are obtained. Error analysis has also been performed and presented in tabular form. The physical clarifications for the behavior of fluid velocity, temperature, skin friction coefficient and Nusselt number are well demonstrated with the help of graphs and contour plots. One of the major outcomes of the present study signifies that water-based SWCNTs have a tendency to cause less drag and higher rate of heat transfer as compared to water-based MWCNTs. This investigation finds numerous applications in different mechanisms of thermal conversion for nuclear propulsion and spacecraft.

Localized Triggering of the Insulator-Metal Transition in VO2 Using a Single Carbon Nanotube.

Vanadium dioxide (VO2) has been widely studied for its rich physics and potential applications, undergoing a prominent insulator-metal transition (IMT) near room temperature. The transition mechanism remains highly debated, and little is known about the IMT at nanoscale dimensions. To shed light on this problem, here we use ∼1 nm-wide carbon nanotube (CNT) heaters to trigger the IMT in VO2. Single metallic CNTs switch the adjacent VO2 at less than half the voltage and power required by control devices without a CNT, with switching power as low as ∼85 μW at 300 nm device lengths. We also obtain potential and temperature maps of devices during operation using Kelvin probe microscopy and scanning thermal microscopy. Comparing these with three-dimensional electrothermal simulations, we find that the local heating of the VO2 by the CNT plays a key role in the IMT. These results demonstrate the ability to trigger IMT in VO2 using nanoscale heaters and highlight the significance of thermal engineering to improve device behavior.

The effect of graphene oxide and functionalized carbon nanotubes as additives on extraction of doxorubicin by polyethylene glycol 6000 / sodium salts aqueous two-phase systems

In this work, the partitioning behavior of Doxorubicin, an antineoplastic drug, has been investigated in the polymer-salt aqueous two-phase systems (ATPSs), and the ability of three nanoparticles (NPs) including graphene oxide (GO), functionalized single, and multi-walled carbon nanotube (f-SWCNT and f-MWCNT) as additives for increasing the partition coefficient of the drug was studied. Systems composed of polyethylene glycol (PEG) and four sodium-based salts containing sulphate, tartrate, citrate, and succinate were chosen to form ATPSs at 300 ± 1 K. Firstly, the partition coefficient and yield recovery of Doxorubicin were investigated in the mentioned ATPSs including 16 different initial compositions. Based on the results, the maximum amount of partition coefficient belongs to a system combined of PEG 6000 + sodium tartrate + water. Then the NPs were added to the best tie-lines of each system to investigate their effects. Results show that all used NPs have improved partitioning of Doxorubicin in the range of 80–4000%. The highest amount of enhancement belongs to the system of PEG 6000 + sodium succinate + water in the presence of f-SWCNT. Consequently, the addition of the mentioned NPs to the ATPSs is proposed as an effective solution for improving the extraction efficiency.

Supramolecular Assembly of Oriented Spherulitic Crystals of Conjugated Polymers Surrounding Carbon Nanotube Fibers.

The directed assembly of conjugated polymers into macroscopic organization with controlled orientation and placement is pivotal in improving device performance. Here, the supramolecular assembly of oriented spherulitic crystals of poly(3-butylthiophene) surrounding a single carbon nanotube fiber under controlled solvent evaporation of solution-cast films is reported. Oriented lamellar structures nucleate on the surface of the nanotube fiber in the form of a transcrystalline interphase. The factors influencing the formation of transcrystals are investigated in terms of chemical structure, crystallization temperature, and time. Dynamic process measurements exhibit the linear growth of transcrystals with time. Microstructural analysis of transcrystals reveals individual lamellar organization and crystal polymorphism. The form II modification occurs at low temperatures, while both form I and form II modifications coexist at high temperatures. A possible model is presented to interpret transcrystallization and polymorphism.

Experimental Measurement of Angular and Overlap Dependence of Conduction between Carbon Nanotubes of Identical Chirality and Diameter

Measurement of the angular and overlap dependence of the conduction between two identical carbon nanotubes (CNTs), with the same diameter and chirality, has only been possible through theoretical calculations; however, our observation of increased resistance adjacent to the junction between two CNTs facilitates such measurements. Since electrical resistance was found to increase with increased diameter ratio, applying 10 V to one of dissimilar diameter CNTs results in cleavage at the junction. Manipulation of the resulting identical CNTs (created by cutting a single CNT) allows for the direct measurement of the angular and parallel overlap conduction. Angular (13° < θ < 63°) dependence shows two minima (22° and 44°) and a maximum at 30°, and conduction between parallel CNTs increases with overall tip separation but shows a sinusoidal relationship with contact length, consistent with the concept of atomic scale registry.

Entropy Analysis of Carbon Nanotubes Based Nanofluid Flow Past a Vertical Cone with Thermal Radiation.

Our objective in the present study is to scrutinize the flow of aqueous based nanofluid comprising single and multi-walled carbon nanotubes (CNTs) past a vertical cone encapsulated in a permeable medium with solutal stratification. Moreover, the novelty of the problem is raised by the inclusion of the gyrotactic microorganisms effect combined with entropy generation, chemical reaction, and thermal radiation. The coupled differential equations are attained from the partial differential equations with the help of the similarity transformation technique. The set of conservation equations supported by the associated boundary conditions are solved numerically with the bvp4c MATLAB function. The influence of numerous parameters on the allied distributions is scrutinized, and the fallouts are portrayed graphically in the analysis. The physical quantities of interest including the skin friction coefficient and the rate of heat and mass transfers are evaluated versus essential parameters, and their outcomes are demonstrated in tabulated form. For both types of CNTs, it is witnessed that the velocity of the fluid is decreased for larger values of the magnetic and suction parameters. Moreover, the value of the skin friction coefficient drops versus the augmented bioconvection Rayleigh number. To corroborate the authenticity of the presented model, the obtained results (under some constraints) are compared with an already published paper, and excellent harmony is achieved in this regard.

Ultrashort Dual Colour Laser at 1.55 and 1.88 $\mu$ m by Using a Carbon Nanotube Saturable Absorber

In this letter, we have achieved passive mode-locked lasers at 1.55 and 1.88 μm that can provide ultrashort (pulse duration ~1 ps) pulses by using a single carbon nanotube (CNT) saturable absorber. The fiber cavity that has been constructed is compact, simple, and stable against mechanical perturbation, which makes this laser superior to solid-state lasers. This letter has shown that a CNT saturable absorber is an alternative to graphene and has two mode-locked wavelengths that are approximately 250 nm apart. The resultant laser is useful for applications where compact dual color wavelengths are required.

Exploration of interactions of ‘blood-nano interface’ of carbon-based nanomaterials for biomedical applications

Abstract

Temperature-dependent Electrical Characterization of Single and Dual-gate Flexible Carbon Nanotube Thin Film Transistors

Dual-gate carbon nanotube thin film transistors (CNTTFTs) with hafnium dioxide (HfO2) and silicon dioxide (SiO2) as gate dielectrics and single-gate CNTTFTs of two types both of bottom-gate structure but one with HfO2 as gate dielectric and another with SiO2 as gate dielectric were fabricated on a flexible polyimide substrate using a scalable process. Electrical characteristics of the fabricated devices at elevated temperatures varying from 25 to 120°C were investigated and compared. Both single and dual-gate flexible devices have exhibited p-type characteristics. As the temperature was raised the on-current, off current, subthreshold swing, transconductance and drain conductance of both single and dual-gate devices increased whereas on–off current-ratio and threshold voltages decreased. The devices exhibited deterioration in transconductance and on-current with the increase of channel lengths. The present work illustrates that dual-gate flexible CNTTFTs outperform the single-gate flexible CNTTFTs in all electrical characteristic parameters and have shown the highest gate control over the channel at different temperatures varying from 25 to 120°C. The performance variations of both single and dual-gate flexible devices were less than 3.1% till the temperature of 50°C and were operational as CNTTFTs at temperatures varying from 25 to 120°C. The on–off current ratio, subthreshold swing, and threshold voltages deteriorate highly at temperatures higher than 120°C and also it was investigated that electrical characteristics were not repeatable at temperatures higher than 120°C. The CNTTFTs on the flexible substrate can be used for flexible electronics applications till 120°C.

(Invited) Single Luminescent Carbon Nanotubes Interrogate the Live Brain Extracellular Space at the Nanoscale

The extracellular space (ECS) of the brain represents up to a fifth of brain volume with an undisclosed complex miniaturized topology. While it has long been seen as a passive brain area, it however constitutes an important signaling region for the development, function and communication of neuronal and glial cells. Interestingly, we have identified luminescent single wall carbon nanotubes, as unique nanoreporters to probe the brain extracellular space. This comes from their unique morphological and near-infrared optical properties, which are now well established but also provide a rich platform for improvements. We used super-localization imaging and single particle tracking of luminescent carbon nanotubes to interrogate the local ECS architecture in live brain tissue at the nanoscale[1-3]. In particular, the interplay between the nanotube geometry and the extracellular space local environment allows extracting information about the ECS local viscosity [1, 4]. In this presentation our recent results about the specific ECS properties near identified brain structures [5] (e.g synapses) and in neurodegenerative disease animal models [6] will also be presented.

(Invited) Synthesis and Properties of All SWCNT Metallic Nanotube Wire

Copper and aluminum wire conductors are the principal means of conducting electricity. However, they add weight, possess poor fatigue and corrosion resistance and suffer from electromigration under severe conditions. Carbon nanotube (CNT) conductors have long been thought able to replace metals but still fall short of copper in electrical conductivity. CNT wires have so far displaced metal conductors in only a few high value-added applications. In this presentation, we outline an approach to create CNT conductors that address copper shortcomings. These carbon-based wires are made by a new high rate process to grow all metallic (armchair) CNT single wall tubes which are spun into wire in situ within the reactor all in one step, thereby keeping air away from the contacting surfaces of the tubes. We discuss a model of growth in terms of entropy of formation and radiation induced sympathetic vibration. In all other CNT yarn formation methods known to us, multistep processes are required which add cost or omit spinning. This latter process is necessary to add strength and improve conductivity. The innovations described in this talk include (1) methods for synthesis of nearly all metallic single chirality carbon nanotubes, and (2) the in situ spinning of these nanotubes within the reactor to a finished wire. We describe their properties determined by Raman, TGA, and structure by SEM and TEM. The conductivity of CNT wires depends on CNT alignment, surface contamination, control over the interfaces (Schottky barriers), and density. Yarns made from nanotubes of exactly the same diameters are also expected to pack well in the wire and provide better properties than the more typical random and larger diameters sometimes made. The combination of Boronite’s approach to create all CNT wire from uniform nanotubes with metallic chirality with the increasing commercial pressure to reduce weight, increase strength, and operational temperature, opens up commercial opportunities for very lightweight wiring in applications from aircraft to rotating machinery used at high temperatures. Weight saving in a variety of products is especially important for aircraft, cars, and even for large electric systems required to deliver very high current pulses. Boronite has also developed a unique method for infiltrating CNT spun yarn with copper, silver or aluminum to create electromigration resistant materials that can carry extreme currents.

Carbon Nanotube Fiber Field Emission Array Cathodes

Field emission cathodes made from single bulk carbon nanotube (CNT) fibers have demonstrated high emission currents and long lifetimes. This paper investigates the goal of achieving even higher current levels from field emission array (FEA) cathodes comprised of multiple CNT fibers arranged in various array configurations. Arrays were fabricated with 25- $\mu \text{m}$ -diameter CNT fibers in 2-fiber ( $1 \times 2$ ), 4-fiber ( $2 \times 2$ ), and 25-fiber ( $5 \times 5$ ) configurations, and their field emission properties were measured. The $1 \times 2$ and $2 \times 2$ FEA cathodes achieved the maximum current values that scaled to greater than 2 mA per emitter. The $5 \times 5$ FEA cathode achieved a high maximum current value of 22 mA and exhibited stable emission for 10 h at ~9 mA at an applied field strength of 0.11 V/ $\mu \text{m}$ . The Fowler–Nordheim theory was used to calculate the effective field enhancement factor ( $\beta _{\mathrm {eff}}$ ) values for all of the arrays. Electrostatic simulations were performed using COMSOL Multiphysics modeling software to model the field enhancement of a perfectly uniform $5 \times 5$ array. The $\beta _{\mathrm {eff}}$ value for the total array was compared to the individual $\beta $ values at the fiber tips predicted by a surface potential model that predicted the field amplification of all 25 CNT fibers in the array.

Instigated magnetic field effect on carbon nanotubes suspensions encompassing variable thermophysical characteristics

This communication aims to explore the instigated magnetic field and partial slip influence on nanofluid transport towards the curved stretching surface by taking into the account temperature and nanoparticles volume fraction dependent viscosity. The single and multi-wall carbon nanotubes (CNTs) are incorporated in the traditional industrial fluids namely, water and propylene glycol. The Curvilinear coordinate system is opted to model the physical flow problem and simplification is performed by utilizing appropriate transformation. The velocity, pressure, induced magnetic field and temperature distributions accompanied by surface drag force and heat flux are computed numerically by employing implicit finite difference scheme. Graphs and bar charts are drawn to examine the effects of prominent substantial parameters. Some pivotal findings are that the Nusselt number was increasing function of ϕ,λ* and Rd and decreasing function of k and N. The present study is a prototype and a benchmark in exploring induced magnetic field effects on CNTs transport over a curved surface and will lead to further investigation in future and may be beneficial in polymer industry and nanotechnology.

Online Characterization of Single Airborne Carbon Nanotube Particles Using Optical Trapping Raman Spectroscopy.

Carbon nanotubes (CNTs) have become recognized as a potential environmental and health hazard as their applications are broadening and manufacturing costs are reducing. Fundamental information of CNTs in air is of significant importance to our understanding of their environmental fate as well as to further applications. Extensive efforts have been made over decades on characterizing CNTs; however, a majority of the studies are of bulk or CNTs dispersed on substrates. In the present study, we characterize single CNT particles in air using optical trapping Raman spectroscopy (OT-RS). Different types of CNT particles, as well as glassy carbon spheres, were optically trapped in air. Their physical properties were viewed by microscopic bright field images and scattering images; their chemical properties and structural information can be inferred from characteristic Raman bands. The system can also spatially resolve the morphology and chemical distribution of optically trapped CNT particles in air. The OT-RS technique combines single-particle morphological and chemical information and offers an online method to characterize the physicochemical properties of single CNT particles at their native states in air.

Carbon nanotube arrays as multilayer transverse flow carbon nanotube membrane for efficient desalination

Although single layer transverse flow carbon nanotube (CNT) membrane (TFCM) has been shown to be ultra-permeable with high salt rejection, its physical fabrication with sub-nanometre slits remains a significant challenge to its development. This work presents the multilayer TFCM, which resembles vertically aligned CNT arrays, as an alternative candidate for efficient desalination. Using molecular dynamics, this work shows that multilayer TFCM can provide permeability and salt rejection on par with its single layer counterpart. By multilayering, the slit size between neighbouring CNTs can be increased to nanometre range while still maintaining high salt rejection. The increase in slit size counteracts the reduction in permeability due to multilayering, thereby allowing multilayer TFCM to achieve permeability performance comparable to the single layer TFCM. The effects of the number of layers n and other design parameters (interlayer distance d, CNT diameter DCNT, offset h) on the desalination performance of multilayer TFCM are investigated thoroughly using results from non-equilibrium and equilibrium molecular dynamics. It was found that the desalination performance is not sensitive to variations in d,DCNT or h. Finally, this work provides computational evidence that the multilayer TFCM, which could be fabricated using techniques for current dense vertically aligned CNT arrays, can make an efficient design for future low dimensional materials membrane.

Two-dimensional graphene oxide-reinforced porous biodegradable polymeric nanocomposites for bone tissue engineering.

This study investigates the mechanical properties and in vitro cytotoxicity of two-dimensional (2D) graphene oxide nanoribbons and nanoplatelets (GONRs and GONPs) reinforced porous polymeric nanocomposites. Highly porous poly(propylene fumarate) (PPF) nanocomposites were prepared by dispersing 0.2 wt % single- and multiwalled SONRs (SWGONRs and MWGONRs) and GONPs. The mechanical properties of scaffolds were characterized using compression testing and in vitro cytocompatibility was assessed using QuantiFlour assay for cellularity and PrestoBlue assay for cell viability. Immunofluorescence was used to assess collagen-I expression and deposition in the extracellular matrix. Porous PPF scaffolds were used as a baseline control and porous single and multiwalled carbon nanotubes (SWCNTs and MWCNTs) reinforced nanocomposites were used as positive controls. Results show that incorporation of 2D graphene nanomaterials leads to an increase in the mechanical properties of porous PPF nanocomposites with following the trend: MWGONRs > GONPs > SWGONRs > MWCNTs > SWCNTs > PPF control. MWGONRs showed the best enhancement of compressive mechanical properties with increases of up to 26% in compressive modulus (i.e., Young's modulus), ~60% in yield strength, and ~24% in the ultimate compressive strength. Addition of 2D nanomaterials did not alter the cytocompatibility of porous PPF nanocomposites. Furthermore, PPF nanocomposites reinforced with SWGONRs, MWGONRs, and GONPs show an improvement in the adsorption of collagen-I compared to PPF baseline control. The results of this study show that 2D graphene nanomaterial reinforced porous PPF nanocomposites possess superior mechanical properties, cytocompatibility, and increased protein adsorption. The favorable cytocompatibility results opens avenues for in vivo safety and efficacy studies for bone tissue engineering applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1143-1153, 2019.

Nanoscale exploration of the extracellular space in the live brain by combining single carbon nanotube tracking and super-resolution imaging analysis.

The brain extracellular space (ECS) is a system of narrow compartments whose intricate nanometric structure has remained elusive until very recently. Understanding such a complex organisation represents a technological challenge that requires a technique able to resolve these nanoscopic spaces and simultaneously characterize their rheological properties. We recently used single-walled carbon nanotubes (SWCNTs) as near-infrared fluorescent probes to map with nanoscale precision the local organization and rheology of the ECS. Here we expand our method by tracking single nanotubes through super-resolution imaging in rat organotypic hippocampal slices and acute brain slices from adult mice, pioneering the exploration of the adult brain ECS at the nanoscale. We found a highly heterogeneous ECS, where local rheological properties can change drastically within few nanometres. Our results suggest differences in local ECS diffusion environments in organotypic slices when compared to adult mouse slices. Data obtained from super-resolved maps of the SWCNT trajectories indicate that ECS widths may vary between brain tissue models, with a looser, less crowded nano-environment in organotypic cultured slices.

Experimental observation of the far field diffraction patterns of functionalization single and multi-walled carbon nanotubes using nonlinear diffraction technique

Nonlinear diffraction pattern can be induced by focusing CWlaser into a thin quartzes cuvette containing nanofluid. The numberof revealed pattern rings indicates to the nonlinear behavior of fluid.Here, the nonlinear refractive index of each of functionalized singlewall carbon nanotube (F-SWCNTs) suspention and multi wall carbonnanotube (F-MWCNTs) suspention have been investigatedexperimentally .Each of CNTs suspention was at volume fraction of13×10−5 and 6×10−5. Moreover the laser source at wavelength of473 nm was used. The results show that SWCNTs suspentionpossesses higher nonlinearty than other at the same volume fraction

Three dimensional Darcy-Forchheimer radiated flow of single and multiwall carbon nanotubes over a rotating stretchable disk with convective heat generation and absorption

Several important characteristics of CNTs (carbon nanotubes) like excellent electrical conductivities, extraordinary thermal conductivities, good mechanical and chemical stability and extremely light mass make CNTs a model material which is utilized in various electro-chemical mechanisms. Keeping the said significance of carbon nanotubes in notice our main aim in this analysis is to establish the import relation of Darcy Forchheimer in three dimensional (3D) flows of classical fluid (water) based CNTs in presence of slip velocity due to rotating stretchable disk. Analysis of nanoparticles like single and multi-walled (SWCNTs, MWCNTs) carbon nanotubes are developed and equated. Present investigation further comprises non-linear thermal radiation, heat generation/absorption as well as convective thermal boundary condition aspects. The pertinent non-linear ordinary differential equations after utilizing the appropriate variables are calculated. HAM (Homotopy Analysis Method) technique is utilized for the analysis of velocities and thermal distribution. Various graphs have been plotted in order to examine that by what means the velocities and thermal field are altered by different model quantities. The main features of flow like the CFReα, CGReα (skin friction), Nu(Reα)−1/2 (heat transfer rate) have been intended numerically and graphically.

Mixed convection in a lid-driven cavity filled with single and multiple-walled carbon nanotubes nanofluid having an inner elliptic obstacle

In this study, numerical analysis and optimization in a single and multiple walled carbon nanotube-water nanofluid filled lid driven cavity having an inner elliptic obstacle were performed by using finite element method and COBYLA optimization solver. The top wall is moving with constant speed and vertical walls are kept at constant temperatures. An optimal size of the inner elliptic obstacle was determined by using an optimization study to maximize the average heat transfer along the hot wall of the cavity. Numerical simulation was performed by for various values of Richardson numbers (between 0.05 and 50) and various solid particle volume fraction (between 0 and 0.06) for single and multiple-walled carbon nanotubes water nanofluid. A larger obstacle (higher values of radii in the major and minor axis) with lower values of Richardson number results in higher heat transfer rates. The average Nusselt number versus solid particle volume fraction shows a linear trend and the discrepancy between the average Nusselt number for the cavity with the optimized obstacle and other obstacles becomes higher with higher particle volume fraction. The average heat transfer enhances significantly which is about 120.20% for single wall carbon nanotube -water nanofluid at solid volume fraction of 0.06 when compared to pure water. The discrepancy between the average Nusselt number for single and multiple walled carbon nanotubes becomes higher for higher values of Richardson number and solid particle volume fraction. A polynomial type correlation was proposed for the average Nusselt number along the hot wall which is fifth order for Richardson number an first order for nanoparticle volume fraction.