Carbon Nanotubes Of Different Diameters Research Articles

Supramolecular Self-Assembly of Dipalmitoylphosphatidylcholine and Carbon Nanotubes: A Dissipative Particle Dynamics Simulation Study.

Dissipative particle dynamics simulations were performed to investigate the self-assembly of dipalmitoylphosphatidylcholine (DPPC) as a model lipid membrane on the surface of carbon nanotubes (CNTs). The influence of surface curvature of CNTs on self-assembly was investigated by performing simulations on solutions of DPPC in water in contact with CNTs of different diameters: CNT (10, 10), CNT (14, 14), CNT (20, 20), and CNT (34, 34). DPPC solutions with a wide range of concentrations were chosen to allow for formation of lipid structures of various surface densities, ranging from a submonolayer to a well-organized monolayer and a CNT covered with a lipid monolayer immersed in a planar lipid bilayer. Our results are indicative of a sequence of phase-ordering processes for DPPC on the surface of CNTs. At low surface coverages, the majority of hydrocarbon tail groups of DPPC are in contact with the CNT surface. Increasing the surface coverage leads to the formation of hemimicellar aggregates, and at high surface coverages close to the saturation limit, an organized lipid monolayer self-assembles. An examination of the mechanism of self-assembly reveals a two-step mechanism. The first step involves densification of DPPC on the CNT surface. Here, the lipid molecules do not adopt the order of the target phase (lipid monolayer on the CNT surface). In the second step, when the lipid density on the CNT surface is above a threshold value (close to saturation), the lipid molecules reorient themselves to form an organized monolayer around the tube. Here, the DPPC molecules adopt stretched conformations normal to the surface, the end hydrocarbon groups adsorb on the surface, and the head groups occupy the outermost part of the monolayer. The saturation density and the degree of lipid ordering on the CNT surface depend on the surface curvature. The saturation density increases with increased surface curvature, and better-ordered structures are formed on less curved surfaces.

Effect of Carbon Nanotube Size on Electrical Properties of Cement Mortar under Different Temperatures and Water Content

The effects of temperature and water content on the electrical conductivity of cement mortar with different sizes of carbon nanotubes were studied, and the effect of the size of carbon nanotubes on the electrical conductivity of cement mortar was revealed. The results show that the small diameter carbon nanotubes have the best enhancement effect on the electrical conductivity of cement mortar. The electrical conductivity of cement mortar with different diameters of carbon nanotubes is positively correlated with water content, and with the decrease of the diameter of carbon nanotubes in the sample, the effect of water content on the electrical conductivity of carbon nanotube cement mortar becomes smaller and smaller. With the increase of temperature, the electrical conductivity of cement mortar containing carbon nanotubes of different diameters increases in varying degrees, but the increase of samples with small diameter carbon nanotubes is the smallest, indicating that the electrical conductivity of cement mortars with small diameter carbon nanotubes is less affected by temperature.

Electrolytical Carbon Nanostructures from Molten Salts: Synthesis and Properties

Carbon nanomaterials (CNMs) occupy a special place in nanoscience owing to exceptional thermal, electrical, chemical and mechanical properties. They are used in various areas of modern technologies: super-strong composite materials, supercapacitors, smart sensors, targeted delivery drugs, catalyst carriers, field emission devices, quantum wires, paints, for energy storing and conversion, for gas storing, in nanoelectronics, etc. Therefore, a great attention is given all over the world to the development of novel efficient method for the fabrication of CNMs, comprehensive investigation of their properties, and search for new applications. Today there are many methods for the synthesis of CNMs. In resent ten years, the method of high-temperature electrochemical synthesis (HTES) in molten salts has been rapidly developing. The essence of the method of HTES is the cathodic reduction of oxygen-containing carbon compounds dissolved in molten salts. There are several variants of HTES. The advantages of all variants of HTES are: (1) soft synthesis conditions, (2) simple hardware implementation, (3) the possibility of controlling the electrolysis conditions, (4) low energy consumption for electrolysis, (5) the use of cheap precursors, (6) easy doping during synthesis, (7) monodipersity of the product. An important advantage of HTES is the possibility of using carbon dioxide as a starting reagent. Global warming, caused by increase in the emission of greenhouse gases (CO2, CH4 and others), is recognized as a serious environmental problem of the mankind.The goal of this work is presentation of research results on the electrochemical transformation of carbon oxy-compounds (lithium carbonate and carbon dioxide) into nanoscale solid carbon of different structure and morphology (carbon nanotubes (CNTs), fibers (CNFs), graphene) in chloride-carbonate melts.On the basis of a voltammetric study, it has been found that direct electroreduction of CO2 dissolved in equimolar salt mixture Na,K|Cl under an excessive pressure (1 - 15 atmospheres) up to carbon at temperature 750 0C occurs in one stage at polarization rates above 0.2 Vs-1. The electrode process is controlled both by the charge transfer rate and by the rate of gas diffusion to the electrode. At polarization rates below 0.1 Vs-1, the electrode process occurs in two stages, and an Electrochemical-Chemical- Electrochemical mechanism of CO2 reduction has been suggested. The cathodic product is carbon films and powders of different structures and morphology. Typical morphologies of the electrolytic products obtained in the melts Na,K|Cl–CO2 are shown in Fig. 1.All the products obtained in the system Na,K|Cl–CO2 (10 atm.) contain CNTs, the majority of which are multi-walled and have a curved form (structural defects). Most often CNTs agglomerate into bundles, and more rarely are arranged as individual tubes. The outer diameter of CNTs varies from 5 to 250 nm, while the internal diameter from 2 to 140 nm. Almost all CNTs are filled partly with electrolyte salt. When the current density increases, the CNT diameter decreases (although every product obtained at the current densities used has CNTs of different diameters).It was found by voltammetry method that the process of reduction of Li2CO3 in Na,K|Cl melt depends on the gaseous atmosphere above the melt. In air, it includes two electrochemical stages. The preliminary chemical reaction of lithium carbonate dissociation (Li2CO3 ⇄ Li2O + CO2) leads to the formation of two electrochemically active particles: CO2 and LixCO3 2-x, which are reduced to elemental carbon at different potentials of -0.8 and -1.7 V respectively against Pt|O2/O2- reference electrode. Both processes are irreversible, and the electroreduction of LixCO3 2-x takes place with diffusion control of the delivery of the depolarizer to the electrode surface. Under of argon or carbon dioxide atmosphere over the melt, the process of lithium carbonate dissociation is suppressed; therefore, the deposition of carbon in this case occurs only from the cationized carbonate complex.X-ray diffraction, SEM and Raman spectroscopy revealed that the cathode product is a high disordered amorphous carbon. Agglomerated particles consist of degraded graphite structures with an approximate crystallite size of 30–40 nm.Figure 1. TEM micrographs (a÷e) and electron-beam images (d (inset in the upper left) and f) of carbon powders produced in the system Na,K|Cl–CO2 (10 atm.) at different current densities: (a ÷ e): i k = 13.5; 28; 42; 56; 72 mA/cm2 ; T = 750 0C; Figure 1

Logarithm Diameter Scaling and Carrier Density Independence of One-Dimensional Luttinger Liquid Plasmon.

Quantum-confined electrons in one-dimensional (1D) metals are described by a Luttinger liquid. The collective charge excitations (i.e., plasmons) in a Luttinger liquid can behave qualitatively different from their conventional counterparts. For example, the Luttinger liquid plasmon velocity is uniquely determined by the electron-electron interaction, which scales logarithmly with the diameter of the 1D material. In addition, the Luttinger liquid plasmon is predicted to be independent of the carrier concentration. Here, we report the observation of such unusual Luttinger liquid plasmon behaviors in metallic single-walled carbon nanotubes, a model system featuring strong electron quantum confinement. We systematically investigate the plasmon propagation in over 30 metallic carbon nanotubes of different diameters using infrared nanoscopy. We establish that the plasmon velocity has a weak logarithm dependence on the nanotube diameter, as predicted by the Luttinger liquid theory. We further study the plasmon excitation as a function of the carrier density in electrostatically gated metallic carbon nanotubes and demonstrate that the plasmon velocity is completely independent of the carrier density. These behaviors are in striking contrast to conventional plasmons in 1D metallic shells, where the plasmon dispersion changes dramatically with the metal electron density and the 1D diameter. The unusual behaviors of Luttinger liquid plasmon may enable novel nanophotonic applications based on carbon nanotubes.

Effects of microwave irradiation on multiwalled carbon nanotubes of different diameters

We have studied the visible and infrared radiation emitted by multi-walled carbon nano-tubes of different diameters when exposed to 2.45 GHz microwaves. A comparison of the spectra suggests that multi-walled carbon nano-tubes with larger diameters emit radiation of greater intensity than those with smaller diameters. Furthermore, the multi-walled carbon nano-tubes continued to emit visible and infrared radiation over the course of several microwave-irradiation cycles, with no degradation in the intensity of the emitted radiation. A comparison of Raman D- to G-band peak-intensity ratios revealed that microwave-irradiation did not significantly impact the multi-walled carbon nano-tubes' defect densities. The results of our experiments suggest that multi-walled carbon nano-tubes may have the potential for use in lighting technologies, and that ohmic heating caused by the polarization of the multi-walled carbon nano-tubes in the microwave field is likely responsible for the observed emissions of visible and infrared radiation.

Electronic transport through defective semiconducting carbon nanotubes

We investigate the electronic transport properties of semiconducting (m, n) carbon nanotubes (CNTs) on the mesoscopic length scale with arbitrarily distributed realistic defects. The study is done by performing quantum transport calculations based on recursive Green’s function techniques and an underlying density-functional-based tight-binding model for the description of the electronic structure. Zigzag CNTs as well as chiral CNTs of different diameter are considered. Different defects are exemplarily represented by monovacancies and divacancies. We show the energy-dependent transmission and the temperature-dependent conductance as a function of the number of defects. In the limit of many defetcs, the transport is described by strong localization. Corresponding localization lengths are calculated (energy dependent and temperature dependent) and systematically compared for a large number of CNTs. It is shown, that a distinction by (m − n)mod 3 has to be drawn in order to classify CNTs with different bandgaps. Besides this, the localization length for a given defect probability per unit cell depends linearly on the CNT diameter, but not on the CNT chirality. Finally, elastic mean free paths in the diffusive regime are computed for the limit of few defects, yielding qualitatively same statements.

Buckling behaviors of metal nanowires encapsulating carbon nanotubes by considering surface/interface effects from a refined beam model

We develop a refined beam model to describe the buckling characteristics of hollow metal nanowires encapsulating carbon nanotubes (NWs@CNTs), where the interfacial van der Waals (vdW) interaction, interfacial shear stress as well as surface effect are taken into consideration. The analytical expressions for cohesive energies of the vdW interaction between carbon nanotubes (CNTs) and hollow nanowires are obtained through continuum modeling. The interfacial shear coefficients for NWs@CNTs with CNTs of different diameters and nanowires of different lattice orientations are derived by molecular dynamics simulations. The surface effects of nanowires are addressed by a function of the bulk surface energy density and surface relaxation parameter. The present results show that all the aforementioned three factors play key roles in the buckling behaviors of NWs@CNTs. In particular, the competition between CNTs and nanowires owing to the coupling effect of the three factors dominates their buckling patterns. This study may provide a theoretical support to prepare vertically aligned CNT arrays with nanoscale conformal coatings and to understand the stability and reliability of CNT reinforced composites.

High Interfacial Barriers at Narrow Carbon Nanotube-Water Interfaces.

Water displays anomalous fast diffusion in narrow carbon nanotubes (CNTs), a behavior that has been reproduced in both experimental and simulation studies. However, little is reported on the effect of bulk water-CNT interfaces, which is critical to exploiting the fast transport of water across narrow carbon nanotubes in actual applications. Using molecular dynamics simulations, we investigate here the effect of such interfaces on the transport of water across arm-chair CNTs of different diameters. Our results demonstrate that diffusion of water is significantly retarded in narrow CNTs due to bulk regions near the pore entrance. The slowdown of dynamics can be attributed to the presence of large energy barriers at bulk water-CNT interfaces. The presence of such intense barriers at the bulk-CNT interface arises due to the entropy contrast between the bulk and confined regions, with water molecules undergoing high translational and rotational entropy gain on entering from the bulk to the CNT interior. The intensity of such energy barriers decreases with increase in CNT diameter. These results are very important for emerging technological applications of CNTs and other nanoscale materials, such as in nanofluidics, water purification, nanofiltration, and desalination, as well as for biological transport processes.

N⁻₃ azide anion confined inside finite-size carbon nanotubes.

In this work, the confinement of an N[Formula: see text] azide anion inside finite-size single-wall zigzag and armchair carbon nanotubes of different diameters has been studied by wave function and density functional theory. Unrelaxed and relaxed interaction energies have been computed, resulting in a favorable interaction between the guest and host system. In particular, the largest interaction has been observed for the confinement in an armchair (5,5) carbon nanotube, for which a natural population analysis as well as an investigation based on the molecular electrostatic potential has been carried out. The nature of the interaction between the two fragments appears to be mainly electrostatic, favored by the enhanced polarizability of the nanotube wall treated as a finite system and passivated by hydrogen atoms. The results obtained are promising for possible applications of this complex as a starting point for the stabilization of larger polynitrogen compounds, suitable as a high-energy density material.

Chiral SWCNT for Ammonia Sensor Application

Gas adsorption in carbon nanotubes is an interesting issue as it affects both the electrical and chemical properties of nanotubes. This effect can be exploited for designing different types of nanosensors. In this paper, chiral carbon nanotubes of different diameters and chiral angle have been considered to investigate the effect of chirality on the sensing capability of single walled carbon nanotubes. Here, the adsorption binding energy of ammonia has been estimated in each tube of varying dimension. The electrical conductivity change and sensitivity of nanotube due to ammonia adsorption has also been calculated. The results are compared with that of achiral tubes of same size. Based on the observations, it has been concluded that (8,3) chiral carbon nanotube is more suitable for ammonia sensor application.

Observation of extreme phase transition temperatures of water confined inside isolated carbon nanotubes.

Fluid phase transitions inside single, isolated carbon nanotubes are predicted to deviate substantially from classical thermodynamics. This behaviour enables the study of ice nanotubes and the exploration of their potential applications. Here we report measurements of the phase boundaries of water confined within six isolated carbon nanotubes of different diameters (1.05, 1.06, 1.15, 1.24, 1.44 and 1.52 nm) using Raman spectroscopy. The results reveal an exquisite sensitivity to diameter and substantially larger temperature elevations of the freezing transition (by as much as 100 °C) than have been theoretically predicted. Dynamic water filling and reversible freezing transitions were marked by 2-5 cm-1 shifts in the radial breathing mode frequency, revealing reversible melting bracketed to 105-151 °C and 87-117 °C for 1.05 and 1.06 nm single-walled carbon nanotubes, respectively. Near-ambient phase changes were observed for 1.44 and 1.52 nm nanotubes, bracketed between 15-49 °C and 3-30 °C, respectively, whereas the depression of the freezing point was observed for the 1.15 nm nanotube between -35 and 10 °C. We also find that the interior aqueous phase reversibly decreases the axial thermal conductivity of the nanotube by as much as 500%, allowing digital control of the heat flux.

(Invited) A Carbon-Carbon Hybrid Immobilizing Carbon Nanodots and Carbon Nanotubes

The thrust of this work is to integrate small and uniformly sized carbon nanodots (CND) with single-walled carbon nanotubes of different diameters as electron acceptors and electron donors, respectively, and to test their synergetic interactions in terms of optoelectronic devices. CNDs were prepared by pressure-controlled microwave decomposition of citric acid and urea. CNDs were immobilized on single-walled carbon nanotubes by wrapping the latter with poly(4-vinylbenzyl trimethylamine) (PVBTA), which features positively charged ammonium groups in the backbone. Negatively charged surface groups on the CNDs lead to attractive electrostatic interactions. Ground state interactions between CNDs and SWCNTs were confirmed by a full-fledged photophysical investigation based on steady-state and time-resolved techniques. As a complement charge injection into the SWCNTs upon photoexcitation was investigated by ultra-short time-resolved spectroscopy.

Comparative Study Of Thermal Stability Of Filled And Un-filled Multiwalled Carbon Nanotubes

Filled or un-filled multiwalled carbon nanotubes (CNTs) used in this study have been synthesized by the floating catalyst method and fixed catalyst method, respectively. The thermal stability of filled/un-filled carbon nanotubes has been investigated by using Thermogravimetric analysis (TGA) and Derivative thermogravimetric (DTG) analysis. In this report, we have developed a methodology to distinguish between filled and un-filled carbon nanotubes. Filled-CNTs are found to be more resistant to oxidation than the un-filled carbon nanotubes. The calculated activation energy of as-grown filled CNTs, by using differential method, determined to be 3.29 ± 0.04 eV, which is higher than that of highly ordered pyrolytic graphite (HOPG). Carboneous impurities; amorphous carbon, catalyst and CNT of different diameter, which are structurally different, are identified by their reactivity and the resistance to oxidation. Copyright © 2016 VBRI Press.

Periodic Crystallisation of Polymers on Carbon Nanotubes: Geometrical Confinement versus Epitaxy

The objective of the study described here is to address the fundamental mechanism of periodic crystallisation of polymer on carbon nanotubes (CNTs), where the polymer-CNT interface adhesion is derived from electrostatic and van der Waals interaction in the resultant hybrid nanoscale architecture. A theoretical analysis of different possibilities of nucleation of a model polymer on CNTs underscores that the periodic nucleation of polymers on CNTs is a geometrical confinement effect rather than a representative of an epitaxial process. The conclusion derived from the theoretical analysis is consistent with the experimental observation made with CNTs of different diameters.

Translocation of LRP1 targeted carbon nanotubes of different diameters across the blood–brain barrier in vitro and in vivo

Brain glioblastoma and neurodegenerative diseases are still largely untreated due to the inability of most drugs to cross the blood–brain barrier (BBB). Nanoparticles have emerged as promising tools for drug delivery applications to the brain; in particular carbon nanotubes (CNTs) that have shown an intrinsic ability to cross the BBB in vitro and in vivo. Angiopep-2 (ANG), a ligand for the low-density lipoprotein receptor-related protein-1 (LRP1), has also shown promising results as a targeting ligand for brain delivery using nanoparticles (NPs). Here, we investigate the ability of ANG-targeted chemically-functionalised multi-walled carbon nanotubes (f-MWNTs) to cross the BBB in vitro and in vivo. ANG was conjugated to wide and thin f-MWNTs creating w-MWNT-ANG and t-MWNT-ANG, respectively. All f-MWNTs were radiolabelled to facilitate quantitative analyses by γ-scintigraphy. ANG conjugation to f-MWNTs enhanced BBB transport of w- and t-MWNTs-ANG compared to their non-targeted equivalents using an in vitro co-cultured BBB model consisting of primary porcine brain endothelial cells (PBEC) and primary rat astrocytes. Additionally, following intravenous administration w-MWNTs-ANG showed significantly higher whole brain uptake than the non-targeted w-MWNT in vivo reaching ~2% injected dose per g of brain (%ID/g) within the first hour post-injection. Furthermore, using a syngeneic glioma model, w-MWNT-ANG showed enhanced uptake in glioma brain compared to normal brain at 24h post-injection. t-MWNTs-ANG, on the other hand, showed higher brain accumulation than w-MWNTs. However, no significant differences were observed between t-MWNT and t-MWNT-ANG indicating the importance of f-MWNTs diameter towards their brain accumulation. The inherent brain accumulation ability of f-MWNTs coupled with improved brain-targeting by ANG favours the future clinical applications of f-MWNT-ANG to deliver active therapeutics for brain glioma therapy.

New Nanobiocomposite Materials for Bioelectronic Devices

We have developed and synthesized nanobiocomposite materials based on graphene, poly(3,4-ethylenedioxythiophene), and glucose oxidase immobilized on the surface of various nanomaterials (gold nanoparticles and multi-walled carbon nanotubes) of different sizes (carbon nanotubes of different diameters). Comparative studies of the possible influence of the nanomaterial's nature on the bioelectrocatalytic characteristics of glucose- oxidizing bioanodes in a neutral phosphate buffer solution demonstrated that the bioelectrocatalytic current densities of nanocomposite-based bioanodes are only weakly dependent on the size of the nanomaterial and are primarily defined by its nature. The developed nanobiocomposites are promising materials for new bioelectronic devices due to the ease in adjusting their capacitive and bioelectrocatalytic characteristics, which allows one to use them for the production of dual-function electrodes: i.e., electrodes which are capable of generating and storing electric power simultaneously.

A carbon-carbon hybrid - immobilizing carbon nanodots onto carbon nanotubes.

The thrust of this work is to integrate small and uniformly sized carbon nanodots (CNDs) with single-walled carbon nanotubes (SWCNT) of different diameters as electron donors and electron acceptors, respectively, and to test their synergetic interactions in terms of optoelectronic devices. CNDs (denoted pCNDs, where p indicates pressure) were prepared by pressure-controlled microwave decomposition of citric acid and urea. pCNDs were immobilized on single-walled carbon nanotubes by wrapping the latter with poly(4-vinylbenzyl trimethylamine) (PVBTA), which features positively charged ammonium groups in the backbone. Negatively charged surface groups on the CNDs lead to attractive electrostatic interactions. Ground state interactions between the CNDs and SWCNTs were confirmed by a full-fledged photophysical investigation based on steady-state and time-resolved techniques. As a complement, charge injection into the SWCNTs upon photoexcitation was investigated by ultra-short time-resolved spectroscopy.

Effect of type and aspect ratio of different carbon nanotubes on cure behavior of epoxy-based nanocomposites

Effect of incorporation of carbon nanotubes (CNTs) into diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin (HY5052/LY5052 system) on cure reaction was investigated via thermal analysis. Keeping their length constant, CNTs of different diameters were chosen. Samples based on epoxy resin and different type and content of CNTs were prepared and characterized. The cure behavior of epoxy matrix in the presence of CNTs was studied in both glassy and rubbery states. The results indicated that the final cure characteristics of epoxy nanocomposites were controlled by the competition of viscosity-increasing effect and heat-sink effect of CNTs. Isothermal analysis showed that accelerating or decelerating effect of CNTs on the cure process depends on CNT content, its aspect ratio and temperature of isothermal cure. The presence of the CNTs physically hindered the mobility of the epoxy and hardener monomers preventing the cure reaction (viscosity-increasing effect). In contrast, inherent high thermal conductivity of CNTs can act as a heat sink to accelerate the heat absorption of the epoxy (heat-sink effect). Below glass–rubber transition temperature (Tg), heat-sink effect of CNTs was dominant due to the restricted mobility of polymer chains in glassy state, whereas at temperatures higher than Tg, viscosity-increasing effect was dominant. CNTs physically hindered the mobility of reactive species despite the inherent tendency of polymer chains for long-range molecular motions.

Feasibility of Carbon Nanomaterials as Gas Sensors: a Computational Study

Carbonaceous materials are a promising class of materials for potential application as chemical and bi-omolecule sensors. In this work we have done first principles calculations to study the interaction of various small molecules, such as CO 2 , H 2 O, NH 3 , CH 4 and H 2 , on the surface of carbon nanotubes (CNTs) and graphene in order to study their feasibility as gas sen-sors. Model systems for armchair and zigzag CNTs of different diameter have been considered to study the effect of chirality and curvature of the carbon nanomaterials on binding with these small molecules. Our results reveal that these gas molecules have been weakly physisorbed on the surface and act as charge donors to the carbon nanomaterials. Charge transfer between the gas molecules and the carbon materials impacts the physical properties of the carbon materi-als, which may be traced to their sensitivity. As the gas molecules are physisorbed on the carbon materials, they may be suitable for repetitive sensor operation. Significant changes in the polarizability of the carbon materials have been observed on binding with the gas molecules and monitoring such changes provides valuable guidance in designing optimal gas sensors based on carbon materials that could satisfy the demand in various fields.

Dissociation of oxygen on pristine and nitrogen-doped carbon nanotubes: a spin-polarized density functional study

The oxygen adsorption energies for pristine and N-doped single-walled carbon nanotubes of different diameters.