Size Of Single-walled Carbon Nanotubes Research Articles

The effect of diameter size of single-walled carbon nanotubes on their high-temperature energy storage behaviour in ionic liquid-based electric double-layer capacitors.

We investigated the effect of the diameter size of single-walled carbon nanotubes (SWCNTs), on their high-temperature energy storage behavior in an electric double layer capacitor (EDLC) using the ionic liquid triethyl(2-methoxyethyl) phosphonium bis(trifluoromethylsulfonyl)imide (P222(2O1)-TFSI). We used four SWCNT samples with diameter sizes ranging from 0.8 to 5 nm, and evaluated their electrochemical charge storage behavior through galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). We found that for the SWCNTs with small average diameter of 1 nm, the value of the electrode capacitance measured at a current density of 5 mA g−1 increased from 15.8 at room temperature to 27.5 F g−1 at 150 °C, and the value measured at a current density of 80 mA g−1 increased from 14.0 at room temperature to 22.1 F g−1 at 150 °C. The larger diameter samples on the other hand did not show any significant change in their capacitance with temperature. We calculated the size of the interstitial tube spaces from the Raman spectra of the samples, and used density functional theory (DFT) calculations to estimate the sizes of the cation and anion of the electrolyte. The obtained results suggest that the temperature-induced changes in the electrolyte properties improved the ion accessibility into the otherwise constrained space inside the small diameter SWCNTs, while the spaces inside the larger SWCNTs already provided easily accessible storage sites hence good performance at room temperature, making the increase in temperature of little to no effect on the charge storage performance in such SWCNTs.

Noncovalent Pyrene-Polyethylene Glycol Coatings of Carbon Nanotubes Achieve in Vitro Biocompatibility.

Single-walled carbon nanotubes (SWNTs) have become increasingly exploited in biological applications, such as imaging and drug delivery. The application of SWNTs in biological settings requires the surface chemistry to remain through the low solubility in aqueous media. In this research, a facile approach for the preparation of a polyethylene glycol (PEG)-coated SWNT-based nanocarrier was reported. We focused on the effect of PEG chain length and SWNT size on the cytotoxicity of PEG-coated SWNTs as a superior drug delivery nanovector. First, all-atom molecular dynamics (MD) simulations were employed to explore the stability and behavior of SWNT/pyrene-PEG (SWNT/Pyr-PEG) structures at a molecular level that is not attainable with experiments. The MD studies revealed that (i) π-π stacking interactions between the pyrene bearing PEG molecules and SWNTs are maintained in bulky situations, regardless of PEG molecular weight or SWNT size; (ii) pyrene molecules diffuse over the SWNT surface without detaching; and (iii) both short and long dynamic Pyr-PEG chains have the capability of effectively coating the SWNT surface. In light of the simulations, noncovalent (π-π stacking) assemblies of SWNT/Pyr-PEG with different molecular weights of PEG ( Mw = 2000, 5000, and 12000) were successfully fabricated and characterized. For longer PEG chains, more effective coating of SWNTs was obtained, resulting in more biocompatible SWNT/Pyr-PEG nanomaterials. The number of SWNTs coated by Pyr-PEG was highly dependent on the length of pyrene bearing PEG polymers. Moreover, the short SWNTs showed a higher amount of PEG coating with respect to the long SWNTs. Cell viability results demonstrated a dose-dependent cytotoxicity of coated SWNTs. Short SWNTs coated with longer PEG chains have low cytotoxicity to be used in in vivo studies.

Low Molecular Weight Polypyrmidine for Release and Size Controlled Process of Single-Walled Carbon Nanotubes

A process for controlling the size of Single-walled carbon nanotubes (SWCNTs) sorting was achieved by combining various centrifugation speeds with polypyrimidine’s properties of dispersion and release SWCNTs upon acid treatment. At first, the SWCNTs wrapped by polypyrimidine were sperated into different size by centrifugating at various speeds. Then, these size-selected hybrids were treated with H2SO4 (98 %) to release free SWCNTs from hybrids, meanwhile the copolymer was collected for reuse. The purity of the released size-controlled SWCNTs was found to be higher than the commercial SWCNTs. The simple synthetic procedure of the copolymer, the low cost of H2SO4 and low centrifugation speed allow the process of size-controlled SWCNTs sorting to more practical applications and industrial scaling up.

Size effect of single-walled carbon nanotube on adsorption of perfluorooctanesulfonate

Perfluorooctanesulfonate (PFOS) is a typical persistent organic pollutant of more environmental concerns in the recent years. The adsorption of PFOS on the single-walled carbon nanotube (SWCNT) is studied with molecular dynamics (MD) simulation. The energy and conformational features are investigated via the statistical results from the MD trajectory. The size effect is observed from the adsorption of PFOS both on the inner and the outer surface. The non-bond interaction energy between PFOS and the inner surface of SWCNT is highly related to the diameter of nanotube. The conformation of PFOS is also changed by the sorbent surface. The PFOS molecule adsorbed on the outer surface is affected by the size of SWCNT more gently than that adsorbed in the nanotube. The aliphatic chain contributes most to the adsorption, as it locates more closely to the outer surface than the charged sulfuric group.

Narrow Diameter Distribution of Horizontally Aligned Single-Walled Carbon Nanotubes Grown Using Size-Controlled Gold Nanoparticles

Diameter control of horizontally aligned single-walled carbon nanotubes (SWCNTs) is highly desired for controlling electronic properties and applying SWCNTs to devices. Preparation of size-ordered catalyst nanoparticles is one of the approaches to synthesizing diameter-controlled SWCNTs. We report the narrow size distribution of gold catalyst nanoparticles obtained by thermal annealing. The size of gold nanoparticles on an ST-cut quartz substrate changed dramatically when nanoparticles were annealed in Ar/H2 atmosphere. Almost all the gold nanoparticles diminished in size to less than 2 nm. More than half of them were under 1 nm. The diameters of SWCNTs synthesized from those nanoparticles were narrowly distributed. The average size of SWCNTs was 0.94±0.07 nm. The size correlation between nanoparticles and SWCNTs smaller than 1 nm suggests the possibility of simultaneous control of orientation and diameter of SWCNTs.

Membrane penetration and curvature induced by single-walled carbon nanotubes: the effect of diameter, length, and concentration

We performed coarse-grained (CG) molecular dynamics (MD) simulations of single-walled carbon nanotubes (SWNTs) with lipid bilayers to understand the effect of the SWNT diameter, length, and concentration on membrane curvature and penetration. Starting with different orientations of multiple SWNTs near lipid bilayers, simulations show that SWNTs insert into the bilayer and induce membrane curvature, which is much larger than that observed from previous simulations of a single SWNT. Longer and thicker SWNTs at higher concentration cause larger membrane curvature, indicating the effect of the SWNT size and concentration, in qualitative agreement with experiments. In particular, thicker SWNTs significantly increase the bilayer height and the difference of the projected and contour bilayer areas, decrease the area compressibility, and disorder lipids. When inserted into the bilayer, thinner SWNTs mainly contact the entire tails of lipids, while thicker SWNTs are wrapped mainly by the ending tail-carbons, leading to the larger membrane curvature. This indicates the effect of SWNT diameter on the SWNT-lipid interaction, yielding different extents of membrane curvature. These findings imply that the SWNT-induced membrane penetration and curvature are modulated by a combination of SWNT length, diameter, and concentration.

Self-assembly of double helical nanostructures inside carbon nanotubes

We use molecular dynamics (MD) simulations to show that a DNA-like double helix of two poly(acetylene) (PA) chains can form inside single-walled carbon nanotubes (SWNTs). The computational results indicate that SWNTs can activate and guide the self-assembly of polymer chains, allowing them to adopt a helical configuration in a SWNT through the combined action of the van der Waals potential well and the π-π stacking interaction between the polymer and the inner surface of SWNTs. Meanwhile both the SWNT size and polymer chain stiffness determine the outcome of the nanostructure. Furthermore, we also found that water clusters encourage the self-assembly of PA helical structures in the tube. This molecular model may lead to a better understanding of the formation of a double helix biological molecule inside SWNTs. Alternatively, it could form the basis of a novel nanoscale material by utilizing the 'empty' spaces of SWNTs.

Thermo mechanical buckling analysis of carbon nanotubes on winkler foundation using non-local elasticity theory and DTM

Thermo-mechanical buckling behaviour of Single Walled Carbon Nanotube (SWCNT) on Winkler foundation is reported. Non-local elasticity theory and differential transformation method are applied. Effects of (i) size of SWCNT, (ii) non-local parameter, (iii) Winkler modulus, (iv) boundary conditions and (v) temperature on buckling load are investigated.

Phase transition of nanotube-confined water driven by electric field

The effects of electric field on the phase behaviors of water encapsulated in a thick single-walled carbon nanotube (SWCNT) (diameter = 1.2 nm) have been studied by performing extensive molecular dynamics simulations at atmospheric pressure. We found that liquid water can freeze continuously into either pentagonal or helical solidlike ice nanotube in SWCNT, depending on the strengths of the external electric field applied along the tube axis. Remarkably, the helical one is new ice phase which was not observed previously in the same size of SWCNT in the absence of electric field. Furthermore, a discontinuous solid-solid phase transition is observed between pentagonal and helical ice nanotubes as the strengths of the external electric field changes. The mechanism of electric-field-induced phase transition is discussed. The dependence of ice structures on the chiralities of SWCNTs is also investigated. Finally, we present a phase diagram of confined water in the electric field-temperature plane.

Effect of Cutting and Functionalization of Single-Walled Carbon Nanotubes on Their Dispersion Behaviors

Cutting of single-walled carbon nanotubes (SWCNTs) and their modification with poly (ethylene glycol) and polystyrene were successfully performed through a treatment of the SWCNTs with piranha solutions and monoamine terminated polymers. The shortening and functionalization of SWCNTs were confirmed through size exclusion chromatography and Raman spectroscopy observations. The shortened SWCNTs exhibited more aggregated morphology than as-prepared SWCNTs in scanning electron microscope and atomic force microscope observations. Cutting and functionalization of SWCNTs with different polymer chains effectively tailored their dispersion behaviors in solvents. Polystyrene composite films exhibited improved transparency employing shortened SWCNTs, suggesting that the size of SWCNTs are critical factors in controlling the transparency of polymer composite films.

Preparation of Single-Walled Carbon Nanotube/Silicon Composites and Their Lithium Storage Properties

Single-walled carbon nanotube (SWCNT)/silicon composites were produced from the purified SWCNTs and Si powder by high-energy ball-milling and then electrochemically inserted with Li using Li/(SWCNT/Si) cells. The highest reversible capacity and lowest irreversible capacity of the SWCNT/Si composites were measured to be 1845 and 474 mAh g(-1) after ball-milling for 60 min, respectively. During the charge/discharge process, most of the Li ions were inserted into the SWCNT/Si composites by alloying with Si particles below 0.2 V and extracted from the SWCNT/Si composites by dealloying with Si particles around 0.5 V. The enhanced capacity and cycle performance of the SWCNT/Si composites produced by high-energy ball-milling were due primarily to the fact that SWCNTs provided a flexible conductive matrix, which compensated for the dimensional changes of Si particles during Li insertion and avoided loosening of the interparticle contacts during the crumbling of Si particles. The ball-milling contributed to a decrease in the particle size of SWCNTs and Si particles and to an increase in the electrical contact between SWCNTs and Si particles in the SWCNT/Si composites.

Buckling analysis of single walled carbon nanotube on Winkler foundation using nonlocal elasticity theory and DTM

In the present work differential transformation method (DTM) is used to predict the buckling behaviour of single walled carbon nanotube (SWCNT) on Winkler foundation under various boundary conditions. Four different boundary conditions namely clamped–clamped, simply supported, clamped hinged and clamped free are used to study the critical buckling loads. Effects of (i) size of SWCNT (ii) nonlocal parameter and (iii) Winkler elastic modulus on nonlocal critical buckling loads are being investigated and discussed. The DTM is implemented for the nonlocal SWCNT analyses and this yields results with high degree of accuracy. Further, present method can be applied to linear and nonlinear problems.

Photochemical modification of single-walled carbon nanotubes using HPHMP photoinitiator for enhanced organic solvent dispersion

Photochemical modification of single-walled carbon nanotubes (SWCNTs) was carried out by covalent attachment of 2-propanol-2-yl radicals on the surface of SWCNTs, which were engendered by the photolysis of 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (HPHMP) under ultraviolet (UV) light. Pristine single-walled carbon nanotubes (p-SWCNTs) were dispersed in acetone along with HPHMP photoinitiator. After that, the mixture was irradiated by UV light to generate the free radicals which were introduced onto the surface of SWCNTs. The modification of SWCNTs was supported by UV/visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, thermal gravimetric analysis–mass spectrometry (TGA–MS), and transmission electron microscopy (TEM). UV/visible results revealed the loss of van Hove singularities due to covalent modification. The modification was further verified by FT-IR showing the signals at 3421 and 1100 cm−1 due to stretching and bending of O–H group, respectively. Moreover, other peaks at 2927 and 2858 cm−1 indicated the asymmetric and symmetric stretching modes of aliphatic C–H bond, respectively. Raman spectra illustrated that the intensity ratio of the tangential mode to the disorder mode (IG/ID), for modified SWCNTs (F-SWCNTs), decreased nearly four times than p-SWCNTs. TGA–MS also evidenced the signal corresponding to m/z 59 at 400 °C indicating the presence of 2-propanol-2-yl groups. TEM and dispersibility data demonstrated that the sidewall modification detached the bundled structure, enhanced the dispersion in common organic solvents and retained the original size of SWCNTs without hefty modification, which could cut or damage the nanotubes.

Single-walled carbon nanotube formation on iron oxide catalysts in diffusion flames

Single-walled carbon nanotubes (SWCNTs) are shown to grow rapidly on iron oxide catalysts on the fuel side of an inverse ethylene diffusion flame. The pathway of carbon in the flame is controlled by the flame structure, leading to formation of SWCNTs free of polycyclic aromatic hydrocarbons (PAH) or soot. By using a combination of oxygen-enrichment and fuel dilution, fuel oxidation is favored over pyrolysis, PAH growth, and subsequent soot formation. The inverse configuration of the flame prevents burnout of the SWCNTs while providing a long carbon-rich region for nanotube formation. Furthermore, flame structure is used to control oxidation of the catalyst particles. Iron sub-oxide catalysts are highly active toward SWCNT formation while Fe and Fe2O3 catalysts are less active. This can be understood by considering the effects of particle oxidation on the dissociative adsorption of gas-phase hydrocarbons. The optimum catalyst particle composition and flame conditions were determined in near real-time using a scanning mobility particle sizer (SMPS) to measure the catalyst and SWCNT size distributions. In addition, SMPS results were combined with flame velocity measurement to measure SWCNT growth rates. SWCNTs were found to grow at rates of over 100 μm/s.

Magnetism of Single-Walled Carbon Nanotube with Pd Nanowire

Magnetism of single-walled carbon nanotubes (SWNTs) filled with Pd in pseudo one-dimension is investigated based on the electronic structure obtained using the first-principle calculation. In addition, the stability of Pd nanowire inside SWNT is evaluated through the calculation of binding energy. The Pd monostrand nanowire with the inter-atomic distance of 2.49 A, which shows ferromagnetism in the free-standing state, has the ferromagnetic moment also in the armchair type SWNTs with the diameter lager than 6.9 A although the magnetic moment is smaller than that of the corresponding free-standing Pd nanowire. The pseudo one-dimensional fcc Pd nanowire with the cross section of the (111) plane in the (14, 0) SWNT has ferromagnetic moment, where the inter-atomic distance is elongated by 28% along the longitudinal axis of SWNT compared with the equilibrium distance, so as to adjust the unit cell size of SWNT. However, the Pd(100) nanowire in (8, 8) SWNT does not show ferromagnetism although it has almost the...

Infiltration behaviour of water in a carbon nanotube under external pressure

The wetting behaviour and associated pressure effect of water in single-walled carbon nanotubes (SWCNTs) are investigated through molecular dynamics (MD) simulations. It is found that water molecules can enter SWCNTs via surface diffusion, and the effective infiltration rate increases with pressure. The effect of pressure on infiltration rate is highly non-linear, exhibiting characteristics of both hydrophilic and hydrophobic surfaces. There exists a nominal infiltration pressure that is dependent on the SWCNT size, above which the water flux is significantly increased.

Oxidation of single-walled carbon nanotubes in dilute aqueous solutions by ozone as affected by ultrasound

A clean and simple wet chemical process using dilute aqueous ozone (O 3) solution with or without ultrasound (US) was used to functionalize single-walled carbon nanotubes (SWCNTs). Both O 3 and O 3/US treatments greatly increased the stability of SWCNTs in water. Results of X-ray photoelectron spectroscopy (XPS) showed that the surface oxygen to carbon atomic ratio increased by more than 600% after 72 h of O 3 treatment. Moreover, the effective particle size of SWCNTs was reduced from the initial 4400 to ∼300 and ∼150 nm, after 24 h of O 3 and O 3/US treatment, respectively. The zeta potential of treated SWCNTs decreased from 3.0 to −35.0 mV (at pH 4) after 2 h of treatment with both O 3 and O 3/US. Based on the XPS results, the oxidation pathway was proposed: at the onset of the oxidation reaction, the C C double bond was first converted to C OH which was then oxidized to C O and O C OH concurrently. Oxidation reactions could be described well with first order expressions. Treatment time controlled the extent of surface oxidation and subsequently the stability and dispersion of SWCNTs in water.

Transformation of singlewalled carbon nanotubes to multiwalled carbon nanotubes and onion-like structures by nitric acid treatment

We have obtained various phases during the refluxing process of singlewalled carbon nanotubes (SWNTs) in 30% HNO 3 acid solution at 100 °C. From the similar treatment in HCl acid solution, we observe no structural phase transformation but enlargement of the bundle size of SWNTs. This strongly suggests that the intercalation of nitric acids into the bundles, which is evidenced by the distribution of smaller diameters of bundles, induces the disintegration of tubes by oxidative etching first and the reformation into multiwalled nanotubes, cone-capped phase, and further onion-like structures. The origin of such a transformation mechanism is further discussed.