Conformations of polyglutamate chains near single walled carbon nanotubes.

The nanoindentation of phospholipid (DMPC) layer by the carbon nanotubes (CNTs) of different diameters was studied using steered molecular dynamics (SMD) method. Four carbon nanotubes of different diameters d were used (d ≈ 9.5, 13.5, 16 and 20 A). The nanotubes were pushed through the 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) layer with a constant speed. Three different pulling velocities were applied: 0.5, 1.5 and 2.5 m/s. All simulations were performed at the physiological temperature T = 310 K. The force acting on a nanotube during membrane indentation and work and free energy were calculated, presented and discussed.

On the basis of the recent progress on the sorting of carbon nanotubes' structure with respect to their diameter or number of walls, we investigate by transmission electron microscopy the sorting efficiency, with a comparison with optical absorption spectroscopy measurements. We study density gradient ultracentrifugation sorted single walled or double walled carbon nanotubes, showing obviously the ability to separate carbon nanotubes of different diameters or/and number of walls. This microscopic approach affords accurate information about the sorted samples such as the real mean diameter, the relative concentration of double walled carbon nanotubes over single walled carbon nanotubes, standard deviation, and the real diameter distribution of carbon nanotubes, even beyond any possible accurate analysis from optical absorption spectroscopy. Therefore, we demonstrate that the diameter analysis of the sorted samples by TEM can indeed afford some information about the relevant optical properties of carbon nanotubes.

Aspects of crystal growth within carbon nanotubes

Aligned carbon nanotubes have great potential for advanced nanotube transistors and integrated circuits. In this article, we studied the carbon nanotube alignment mechanism using a chemical vapor deposition growth on a-plane sapphire substrates. We synthesized carbon nanotubes of different diameters by controlling the catalyst size and observed that nanotubes of smaller diameters had a higher degree of alignment. In addition, a surprising observation was that misaligned nanotubes had a preferred orientation. Furthermore, we developed a numerical simulation method to calculate interaction energy between a-plane sapphire surface and carbon nanotubes of different diameters. The calculated results were in good agreement with our experimental observations, which confirmed the observed diameter-dependent alignment and the preferred orientation for misaligned nanotubes.

Carbon nanotubes have caught tremendous attention of the researchers during the last decade due to their excellent mechanical, electrical, optical and thermal prop- erties. The exploitation of these fibers as reinforcing agents in making strong fiber composites has been a primary research topic in the recent investigations on composite materials. Although the theoretical results are rather opti- mistic, the goal of achieving high strength of the carbon nanotube composites is still not satisfactorily realized. We report here a comparative study of the mechanical properties of single-walled, multi-walled and bundle of single-walled carbon nanotubes. Their mechanical behavior is investigated by molecular dynamics simulation, considering Brenner's second generation reactive empirical bond order interatomic potential between the carbon atoms making a tube. For a long range interaction, we have defined a weak van der Waals force which acts between different layers of a multi-walled tube or between different tubes of a bundle. Samples of three isolated armchair single-wall carbon nanotubes of different diameters, a multi-wall armchair carbon nanotube and finally a bundle of three armchair single-walled nanotubes of same diameter are taken. Their fracture pattern and buckling behavior are modeled and compared. Significant changes are observed in the mechanical properties of the samples of different types of carbon nanotubes which arise due to the interaction between the shells of a multi-walled tube or the tubes in a bundle.

As one of the fundamental prerequisites for composite material applications of single-walled carbon nanotubes, their mechanical properties as reinforcing fillers should be identified in the conventional manner of mechanics of composite materials. In particular, identification of elastic properties under axial tension and compression, i.e., initial Young's modulus and Poisson's ratio in terms of longitudinal straining will have a considerable influence on the estimation accuracy of the mechanical (including elastic) properties of carbon nanotube reinforced composites. In this article, elastic properties of unchiral (arm-chair and zig-zag) single-walled carbon nanotubes of different diameters under infinitesimal, small but finite, and large strain regions are numerically computed based on the definition of tube cross-sectional area which will be adopted in the composite materials communities. A classical molecular dynamics simulation using the well-verified Tersoff-type empirical potential for carbon and hydrocarbon molecules is employed. Contrary to what has been reported so far for the case of infinitesimal straining which has been conducted in this study as well, it has been shown that the elastic properties such as initial Young's modulus and Poisson's ratio of the nanotubes in a small but finite strain range should be more or less treated as chirality-dependent, diameter-dependent, and bi-modal ones. The Mooney—Rivlin constants of unchiral carbon nanotubes are also evaluated. From the present results, it is cautioned that the carbon nanotubes are not always stiff and strong when they are looked upon as reinforcing fibers or fillers of composite materials.

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.

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.

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.

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.

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.

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.

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.

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.

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.