Stability Of Single-walled Carbon Nanotubes Research Articles

Single Walled Carbon Nanotube (SWCNT) Detection of Interleukin 1 β (IL-1β)

Single walled carbon nanotubes (SWCNTs) are known for their fluorescent properties in the near-infrared region, as well as their photostability and emission within the “biological transparency window”. This makes them useful as nanosensors for in vivo signal detection. The stability of SWCNTs also allows for repeated, long-term measurements. Implantation of these sensors in vivo allow for detection of biomarkers of specific diseases. Interleukin 1 β (IL-1β) is a pro-inflammatory cytokine involved in pleiotropic cellular processes. IL-1β is commonly found at elevated levels in cancerous tissues and other chronic diseases. We are working to design an IL-1β nanosensor by evaluation of optical band gap changes in the presence of the desired antigen. This is accomplished by conjugating an antibody of interest to the SWCNT wrapped with TAT6-NH2 DNA oligonucleotide and passivating the surface of the SWCNT with bovine serum albumin (BSA). This causes the SWCNT’s hydrophobic surface to be less available for non-specific protein interference, creating a more functional sensor. We observed significant changes in the sensor’s center wavelength and change in fluorescence intensity in the antigen’s presence, serving as an indication of the functionality of the nanosensor. We are also working on studying the capability of fluorescent dyes to exacerbate the wavelength shift seen in SWCNTs. This is accomplished by conjugating the dye to a nanosensor and introducing its complimentary antigen that will remove the dye from the SWCNT surface, intensifying its shift in wavelength. The overall goal of developing this type of nanosensor is to use it in point-of-care scenarios to measure biomarker levels in patient samples or in vivo, allowing for detection of chronic diseases that may be difficult to diagnose early on.

The improvement of yield and thermal stability of single-walled carbon nanotubes fabricated by Gd-assisted FCCVD

In this work, single-walled carbon nanotubes (SWNTs) were synthesized by a scalable floating catalyst chemical vapor deposition (FCCVD) method, in which Gd was used as growth promotor to improve the yield and quality of SWNTs. Based on the characterization results of electron microscope, thermogravimetric analysis and Raman spectroscopy, the application of Gd leads to a great increase in the production of large-diameter SWNTs with a narrow diameter distribution and an enhanced thermal stability. The newly developed FCCVD technique makes it possible to produce large-diameter SWNTs at a low cost, and the generated structurally homogenous SWNTs are suitable for their applications in the fields of electronic systems and electromagnetic shielding, etc.

Development of Quality Control Methods for Dispersibility and Stability of Single-Wall Carbon Nanotubes in an Aqueous Medium.

The attractive properties of single-wall carbon nanotubes (SWCNT) such as mechanical strength and high electrical and thermal conductivity are often undercut by their agglomeration and re-agglomeration tendencies. As a result, the application of SWCNT as additives in advanced composite materials remain far from their potential, with proper dispersion being the major inhibitor. This work presents a dispersion quality control approach for water-based SWCNT dispersions (dispersed by a unique combination of physical and chemical methods), using complementary and easily scalable, characterization methods. UV-Vis spectroscopy, rheological measurements, and precipitant sheet resistance were used to understand the properties of the initial solution through processing and application. From an industrial perspective, these methods are fast and easy to measure while giving a repetitive and quick indication of dispersion quality and stability. The methods were correlated with microscopy and Raman spectroscopy to validate dispersion and SWCNT quality under various dispersing energies. The protocol was then applied to estimate the stability of SWCNT solutions, as well as the effectiveness of different surfactants in aiding dispersion. The simple, fast, and scalable combination of different characterizations provides good SWCNT dispersion and can be used as a quality control system for industrial production and usage.

Stability of single-walled carbon nanotubes toward covalent bonding between the zigzag edges

Edges of single-walled carbon nanotubes (SWCNTs) have unique electronic structure and chemical reactivity that have not been fully explored yet. With help of the DFT and GFN2-xTB electronic structure calculations, we demonstrate for the first time that the zigzag edges of carbon nanotubes are capable of forming direct interlinking covalent bonds between the SWCNTs. The interlinking bond formation is predicted to be feasible for SWCNTs of different length, diameter, and chirality vectors. Covalent linking of SWCNTs might have implications in chemical and mechanical applications of SWCNTs.

An Efficient Method to Completely Remove Catalyst Particles from HiPCO Single Walled Carbon Nanotubes

An efficient, economic and easy method for removing 99% of catalyst particle from high pressure carbon monoxide (HiPCO) single walled carbon nanotubes (SWCNT) is reported. The experiment is carried out at low temperature followed by acid treatment. The process exploited here is oxidation of the carbon impurities to gaseous phase as CO2 and removal of oxidized catalyst debris using acid treatment. Stability of SWCNT at these temperatures does not allow any damage to the nanotubes, however, some damage is observed which can be attributed to the oxidation of catalyst particles and their removal. The purified sample showed very less/no amount of amorphous carbon and catalyst impurities. Characterization of the material was carried out using Raman spectroscopy, Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), Transmission electron microscope (TEM) and Energy Dispersive Spectroscopy (EDAX). The resultant SWCNT were found to be highly pure. EDAX spectroscopy showed that the purified sample had only 0.5wt% of catalyst impurities whereas the as prepared once have 9.09wt%, also, TGA curve of the treated sample showed a very significant increase in the oxidation temperature indicating less defect and less catalyst content in the sample. The non- carbonaceous residue after purification is about 0.3%. highly efficient purification of SWCNT using the proposed method. This work provides a basis on removing the catalyst particles completely.

Contribution of arabinogalactan protein to the stabilization of single-walled carbon nanotubes in aqueous solution of gum arabic

Nowadays, the application of gum arabic has been extended from food industry as a food gum to broad fields including pharmaceutical, personal care and nanomaterials as a versatile agent providing specific physicochemical properties and functional attributes. Despite of its excellent properties, the complex nature of multicomponent of gum arabic may act as an obstacle to understand profoundly its functionality and relevant mechanism in applications. In this study the effect of arabinogalactan protein (AGP), one of the main components in gum arabic, on the stabilization of single-walled carbon nanotubes (SWNTs) in aqueous gum arabic solution has been clarified. By using gel permeation chromatography coupled with multi-angle laser light scattering system (GPC-MALLS), fluorescence spectroscopy, circular dichroism, surface tension measurement and thermogravimetric analysis as well as atomic force microscope and transmission electron microscopy observation, it is found that the adsorption of AGP on the surface of SWNTs contributes to the stability of nanotubes in water by steric hindrance. The AGP physically modified SWNTs also shows improved biocompatibility. The use of AGP for stabilization of SWNTs dispersions may offer advantages of maintaining the initial properties of SWNTs, and providing biocompatibility and highly adhesive interfaces between individual carbon nanotubes and a biopolymeric matrix that are essential for tissue engineering and medical devices.

Aggregation kinetics of single walled carbon nanotubes influenced by the frequency of ultrasound irradiation in the aquatic environment

The colloidal stability of single-walled carbon nanotubes (SWNTs) sonicated at three different ultrasonication (US) frequencies (28, 580, and 1000kHz) were investigated under environmentally relevant conditions. In particular, correlations between surface chemistry, electrokinetic potential, interaction energy, and the aggregation kinetics of the aqueous SWNTs were studied. We observed that H2O2 production is negatively correlated with the yield of hydroxylation and carboxylation of SWNTs, which was dependent on the generation of ultrasonic energy by cavity collapse during US process. The SWNTs sonicated at relatively high US frequencies (580 and 1000kHz) aggregated rapidly in synthetic surface water, whereas alkalinity affected the stability of SWNTs insignificantly. This was because the SWNTs became less negatively charged under such conditions and were captured in deep primary energy wells, according to the Derjaguin-Landau-Verwey-Overbeek theory. Critical coagulation concentration values for the ultrasonicated SWNTs were determined to be 102mM NaCl for 28kHz, 22mM NaCl for 580kHz, and 43mM NaCl for 1000kHz. Suwannee River humic acid decreased the aggregation rate of SWNTs due to the steric hindrance, because of adsorbed macromolecules. Our findings show that the aggregate stability of SWNTs is controlled largely by a complex interplay between the evolution of surface functional groups on the SWNTs during US and solution chemistry.

Hydrogen storage in Titanium-doped single-walled carbon nanotubes with Stone-Wales defects

The hydrogen storage capacity of Titanium-doped single-walled carbon nanotubes (SWCNT) containing the Stone-Wales 5,8 defects was studied using molecular dynamics simulations. The equilibrium doping sites and their stability were estimated using density functional theory. Although introduction of structural defects and dopant atom decreases the formation and cohesive energies, the drop in these energies is not large enough to hinder the thermodynamic feasibility of formation of these structures. Moreover, we observed that the stability of SWCNTs, where Ti is doped by replacing two carbon atoms is similar to that of the defect-free nanotube. This particular novel configuration (D5) was also obtained by rearranging the bonds in the 5 and 8-member rings of the Stone-Wales defect. Doping Ti on the defective rings has a more significant effect on the adsorption of hydrogen than doping on the regular 6-member rings. The D5 SWCNT showed the highest gravimetric and volumetric storage capacities at a temperature of 298K and a moderate pressure of 140atm. We also compared the performance of the D5 SWCNT with a recently reported Ti-doped porphyrin SWCNT and observed that the storage capacity of the D5 SWCNT was significantly higher at similar conditions. Our results suggest that Ti-doped SWCNTs with the Stone-Wales (5,8) defects show a promising potential to meet the ultimate goal set by the US Department of Energy for hydrogen storage.

Length dependent stability of single-walled carbon nanotubes and how it affects their growth

Using density-functional theory the stability of armchair and zigzag single-walled carbon nanotubes and graphene nanoribbons was investigated. We found that the stability of armchair and zigzag nanotubes has different linear dependence with regard to their length, with switches in the most stable chirality occurring at specific lengths for each nanotube series. We explain these dependencies by competing edge and curvature effects. We have found that within each series armchair nanotubes are the most stable at short lengths, while zigzag nanotubes are the most stable at long lengths. These results shed new insights into why (near) armchair nanotubes are the dominant product from catalytic chemical vapor deposition growth, if templating is not used. Paradoxically, the stability of armchair nanotubes at short lengths favors their growth although zigzag nanotubes are more stable at long lengths, resulting in the production of the least stable nanotubes.

A fundamental investigation of the surfactant-stabilized single-walled carbon nanotube/epoxy resin suspensions by molecular dynamics simulation

The surfactant-assisted stabilization of single-walled carbon nanotubes (SWCNTs) in SWCNT/epoxy resin suspensions were investigated for different surfactant types, concentrations, and temperatures using molecular dynamics simulation. One cationic surfactant, i.e. cetyltrimethylammonium bromide (CTAB), and three anionic surfactants, i.e. sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonate (NaDDBS), and sodium cholate (SC), as well as a 1:1 mixture of CTAB and SDS were used. Potentials of mean force (PMFs) were generated between two fixed-size (6,6) SWCNTs for all neat (no surfactant) and surfactant-loaded SWCNT/epoxy resin systems at three different surfactant concentrations (0.25, 0.50, and 1.00 wt%) at room (298 K) and elevated temperature (398 K, only for low-surfactant-concentration systems). Overall, two distinct mechanisms of SWCNT stabilization by the surfactants were identified: (1) an increase in the SWCNT aggregation energy barrier due to the wrapping of the SWCNTs by the surfactant molecules, and (2) a constantly positive free energy (repulsion) for all SWCNT separation distances due to the encapsulation of the two approaching SWCNTs. With the second mechanism, there is a delay for the epoxy molecules to be pushed out from the space between the two SWCNTs. With an increase in the surfactant concentration, the first mechanism becomes more prevalent. With an increase in temperature to 398 K, all surfactants migrate to the suspending medium, thereby the second mechanism of SWCNT stabilization dominates. A drop in the SWCNT-surfactant binding energy is observed around 360–370 K, signifying the surfactant migration to the suspending medium. More or less, all surfactants stabilize the SWCNTs in an epoxy resin at one or more surfactant concentrations. However, NaDDBS exhibits a higher SWCNT aggregation barrier at high concentrations and both temperatures (298 K and 398 K), thereby providing a better SWCNT stabilization in the epoxy resin compared to the other surfactants.

Dynamic stability of single-walled carbon nanotube embedded in a viscoelastic medium under the influence of the axially harmonic load

The nonlinear model of a single-walled carbon nanotube (SWCNT) modeled as a nanobeam embedded in a Kelvin-Voigt viscoelastic medium is developed by using the nonlocal continuum theory. It is assumed that the nanobeam vibrates under the influence of the longitudinal magnetic field and time-varying axial load. Based on the nonlocal Euler-Bernoulli beam theory, Maxwell’s equations and von Karman nonlinear strain-displacements relation, we obtain the nonlinear partial differential equations of transversal motion of the embedded nanobeam with different boundary conditions. The relationship between nonlinear amplitude and frequency of variable axial load in the presence of the longitudinal magnetic field is derived by using the perturbation method of multiple scales. An approximate analytical solution for nonlinear frequency and instability regions for the linear case of vibration is also considered in this paper. In order to analyze nonlinear dynamical stability regions of SWCNT, the incremental harmonic balance (IHB) method is introduced for obtaining iterative relationship of frequency and amplitude of time-varying axial load. It is showed that the nonlocal parameter, magnetic field effects and stiffness coefficient of the viscoelastic medium have significant effects on vibration and stability behavior of nanobeam and therefore receive substantial attention. In addition, from the presented numerical results one can see the influence of the small scale, magnetic field and foundation coefficients on the frequency-response curve, nonlinear frequency and instability regions for the linear and nonlinear cases.

Enhanced dispersion stability of supramolecular complexes of single-walled carbon nanotubes with fluorene-based conjugated polymers

ABSTRACTSupramolecular complexes of single-walled carbon nanotubes (SWNTs) with poly(9,9-didodecylfluorene-2,7-diyl) (PF) derivatives were prepared using a solution dispersion process. A series of novel conjugated PF polymers with carboxyl or hydroxyl end groups at both ends were synthesized by the Yamamoto-type coupling of 2,7-dibromo-9,9-didodecylfluorene using Ni(COD)2 as a catalyst, and further end-capped with either 4-bromobenzoic acid or 4-bromobenzyl alcohol to obtain the end-functionalized PF with different terminal groups. An α-monocarboxy-ω-mono-methoxy poly(ethylene glycol) was connected to both ends of the PF-containing hydroxyl end groups to produce triblock copolymers of poly(ethylene glycol)-b-polyfluorene-b-poly(ethylene glycol) (PEO-b-PF-b-PEO). These SWNTs were completely wrapped with the conjugated polymers through π–π interactions, which enhanced the solubility of the SWNT complexes in organic media, and prevented the aggregation of the polymer–SWNT complexes into large bundles. This indicates that the dispersion stability of SWNTs is enhanced by the addition of the conjugated polymers.

Longitudinal vibration and stability analysis of carbon nanotubes conveying viscous fluid

Nowadays, carbon nanotubes (CNT) play an important role in practical applications in fluidic devices. To this end, researchers have studied various aspects of vibration analysis of a behavior of CNT conveying fluid. In this paper, based on nonlocal elasticity theory, single-walled carbon nanotube (SWCNT) is simulated. To investigate and analyze the effect of internal fluid flow on the longitudinal vibration and stability of SWCNT, the equation of motion for longitudinal vibration is obtained by using Navier-Stokes equations. In the governing equation of motion, the interaction of fluid-structure, dynamic and fluid flow velocity along the axial coordinate of the nanotube and the nano-scale effect of the structure are considered. To solve the nonlocal longitudinal vibration equation, the approximate Galerkin method is employed and appropriate simply supported boundary conditions are applied. The results show that the axial vibrations of the nanotubesstrongly depend on the small-size effect. In addition, the fluid flowing in nanotube causes a decrease in the natural frequency of the system. It is obvious that the system natural frequencies reach zero at lower critical flow velocities as the wave number increases. Moreover, the critical flow velocity decreases as the nonlocal parameter increases.

Chirality-dependent mechanical response of empty and water-filled single-wall carbon nanotubes at high pressure

The mechanical stability of single-wall carbon nanotubes (SWCNTs) at high pressure was studied by high-resolution resonant Raman and wavelength-dependent fluorescence-excitation (PLE) spectroscopy resolving the vibrational and electronic resonances of 18 individual chiralities and furthermore even resolving the different behaviour of empty (closed, pristine) and water-filled (opened) SWCNTs (diameter range = 0.6–1.42 nm). We find that water-filling exerts a stabilizing counter-pressure on the SWCNT walls, leading to an increasing difference between the radial breathing mode frequencies of water-filled and empty SWCNTs at elevated pressures. For small diameter SWCNTs (d < 1 nm) with a chiral angle of ∼12°, in particular for the (7,2) chirality, an anomalous behaviour is observed, revealing an increased mechanical instability for these SWCNTs. We furthermore ascribe the longstanding contradiction between experiments and theory on the collapse pressure of SWCNTs to the presence of filling in most experiments to date, while empty SWCNTs follow the theoretically predicted collapse behaviour.

Numerical stability analysis of imperfect single-walled carbon nanotubes under axial compressive loads

Purpose – A computational structural mechanics approach, based on the exclusive use of standard bar elements is utilized in order to investigate the elastic stability of single-walled carbon nanotubes (SWCNTs) with atom vacancy defects under axial compressive loads. The paper aims to discuss this issue. Design/methodology/approach – The proposed model uses three dimensional, two nodded, linear truss finite elements of three degrees of freedom per node to represent the force field appearing between carbon atoms due to the basic interatomic interactions. Findings – Numerical results concerning the critical forces which cause instability of pristine nanotubes are compared with corresponding data given in the open literature in the effort to demonstrate the good accuracy of the method. Then, it is assumed that SWCNTs present-specific structural defects defined by their length, width, orientation and longitudinal position. The influence of these four geometric parameters of the imperfections considered on the stability of SWCNTs is investigated in detail and essential conclusions are revealed. Originality/value – To the authors’ best knowledge, is the first time that the specific method is introduced for the prediction of buckling behavior of defective SWCNTs. The structural defect here is considered as atoms vacancy that forms a like-crack defect having a specific length, width, orientation and position along the nanotube length.

Optical Microspectroscopy Study of the Mechanical Stability of Empty and Filled Carbon Nanotubes under Hydrostatic Pressure

We present a high-pressure optical and infrared spectroscopy study on the mechanical stability of single-walled carbon nanotubes (SWCNTs) filled with C60 and C70 fullerene molecules (C60- and C70-p...

Analysis of nonlinear dynamic stability of single‐walled carbon nanotubes in thermal environments

Based on the non-local Euler beam theory, the nonlinear dynamic stability of single-walled carbon nanotubes (SWCNTs) embedded in an elastic medium including the thermal effects is presented. The nonlinear dynamic equations and the boundary conditions of the SWCNTs are obtained by using the Hamilton variation principle. By adopting the Galerkin procedure, the governing nonlinear partial differential equation is converted into a nonlinear ordinary differential equation, and then the incremental harmonic balance method is applied to obtain the principal unstable regions of the SWCNTs. In the numerical examples, the effects of the thermal loads, the non-local parameters and the elastic medium on the nonlinear dynamic stability, respectively, are discussed.

Attempts to control depletion in the surfactant-assisted stabilization of single-walled carbon nanotubes

Single-walled carbon nanotubes were stabilized by an anionic surfactant, sometimes in mixture with a nonionic one (Triton TX-100), and/or in presence of salt. The stabilizing activity of sodium dodecylsulfate is poor, with occurrence of phase separation at moderate surfactant content; even lower is the one ascribed to TX-100. We quantified the stabilization in terms of surface coverage by the adsorbing species; the effect is counteracted by the presence of micelles present in the surrounding medium. A chemical approach accounted for the competition between surface adsorption and micelle formation.Destabilization of the dispersions is due to unbalanced osmotic effects and is related to depletion. The above phenomenon occurs when the volume fraction of micellar aggregates reaches a certain threshold, whose value is related to micelle size. Depletion was avoided by selecting the maximum possible amounts of sodium dodecylsulfate, NaCl and/or Triton TX-100. In mixed systems the stabilization is active for longer times compared to dodecylsulfate, although depletion occurs at lower surfactant content.

Prediction of Elastic Mechanical Behavior and Stability of Single-Walled Carbon Nanotubes Using Bar Elements

A computationally effective structural mechanics approach based on the exclusive use of bar elements is developed in order to test its efficiency to predict the elastic longitudinal, torsional, and radial mechanical properties of zigzag, chiral, and armchair single-walled carbon nanotubes (SWCNTs). In addition, the proposed method is used for the investigation of the stability of SWCNTs under compressive and radial loads. The proposed model uses three-dimensional, two-noded, linear bar finite elements of three degrees-of-freedom per node to represent the force field appearing between carbon atoms due to the basic interatomic interactions. The numerical results, which are compared with corresponding data given in the open literature, demonstrate the convergence and stability of the method in predicting the elastic properties and critical forces that cause the instability of the tubes. The effect of chirality, length, and radius of carbon nanotubes on numerical predictions is thoroughly and clearly demonstrated.

Thermal Effect on Dynamic Stability of Single-Walled Carbon Nanotubes in Low and High Temperatures Based on Nonlocal Shell Theory

This paper studies the thermal effect on dynamic stability of single-walled carbon nanotubes (SWCNTs) embedded in polymer matrix in low and high temperatures under impact loads. To this end, we present a nonlocal elastic shell model including thermal and small-size effects. Further, numerical calculations are presented for SWCNTs. Results show that the increasing in temperature field has the effect of increasing the dynamic buckling loads at low or room temperature. However, this effect leads to decrease the dynamic buckling loads at high temperature. In addition, it is observed that nonlocal dynamic buckling loads increase by an increase in the Neperian frequency.