Outer Nanotube Research Articles

Nonlocal vibration and instability analysis of embedded DWCNT conveying fluid under magnetic field with slip conditions consideration

In this study, vibration of double-walled carbon nanotubes (DWCNTs) conveying fluid placed in uniform magnetic field is carried out based on nonlocal elasticity theory. DWCNT is embedded in Pasternak foundation and is simulated as a Timoshenko beam (TB) model which includes rotary inertia and transverse shear deformation in the formulation. Considering slip boundary conditions and van der Waals (vdW) forces between inner and the outer nanotubes, the governing equations of motion are discretized and differential quadrature method (DQM) is applied to obtain the frequency of DWCNTs for clamped–clamped boundary condition. The detailed parametric study is conducted, focusing on the remarkable effects of small scale, Knudsen number, elastic medium, magnetic field, density, and velocity of conveying fluid on the stability of DWCNT. Results indicate that considering slip boundary conditions has significant effect on stability of DWCNTs. Also, it is found that trend of figures have good agreement with the previous researches. Results of this investigation could be applied for optimum design of nano/micro mechanical devices for controlling stability of DWCNTs conveying fluid under magnetic fields.

Analytical solutions to the free vibration of a double-walled carbon nanotube carrying a bacterium at its tip

We calculate the natural frequencies and mode shapes of a cantilevered double-walled carbon nanotube carrying a rigid body—representative of a bacterium or virus—at the tip of the outer nanotube. By idealizing the nanotubes as Bernoulli-Euler beams, we are able to obtain exact expressions for both the mode shapes and characteristic frequency equation. Separate analyses are performed for the special case of a concentrated tip mass and the more complicated situation where the tip body also exhibits inertia and mass center offset from the beam tip.

A nonlocal shell theory model for evaluation of thermoelastic damping in the vibration of a double-walled carbon nanotube

Thermoelastic damping (TED) is a major factor of dissipating energy in the vibration control of nanodevices. On the other hand, application of classic theory in the study of nanostructures is not reasonable. In this paper, a model based on nonlocal shell theory, accounting for the small-scale effects, is used to investigate thermoelastic vibration behavior and damping of double-walled carbon nanotubes (DWCNTs) with simply supported boundary conditions. The inner and outer carbon nanotubes are considered as two individual thin shells. The set of general thermoelastic coupled equations are numerically solved. The results show that the small-scale effects decrease natural frequencies and increase thermoelastic damping compared to the local model, especially for the coaxial frequency and large circumferential wave numbers. The numerical results also show that when the radius of nanotubes rises, the influence of small-size effect on natural frequencies and thermoelastic damping drops dramatically.

Structural and electronic properties of SiC nanotubes filled with Cu nanowires: A first-principles study

The structural and electronic properties of Cun (n=5,9,13) nanowires encapsulated in armchair (8,8) silicon carbon nanotubes (SiCNTs) are investigated using the first principles calculations within the generalized-gradient approximation. We find that the formation processes of these systems are all exothermic. The initial shapes (quadratic–prismatic Cu wire and cylindrical (8,8) SiCNT) are preserved without any visible changes after optimization for the Cu5@(8,8) and Cu9@(8,8) combined systems, but a quadratic-like cross-section shape is formed for the outer nanotube of the Cu13@(8,8) combined system due to the stronger interaction between nanowire and nanotube. The electrons for Si and C atoms in outer SiC sheath affect the electron conductance of the encapsulated metallic nanowire in the Cu13@(8,8) combined system. But in the Cu5@(8,8) and Cu9@(8,8) combined systems, the conduction electrons are distributed only on the copper atoms, so electron transport will occur only through the inner Cu nanowires and the outer inert SiCNTs only function as insulating cable sheaths. Considering the maximal metal filling ratio in nanotube, we know that the Cu9@(8,8) combined system is top-priority in the ultra-large-scale integration (ULSI) circuits and micro-electromechanical systems (MEMS) devices that demand steady transport of electrons.

Surfactant-assisted nanocrystal filling of TiO2 nanotube arrays for dye-sensitized solar cells with improved performance

Uniform, debris-free, fewer-crack, and highly ordered TiO2 nanotube arrays are prepared by a two-step anodic oxidation method, and a surfactant-assisted vacuum impregnation approach is developed to control the incorporation of sub-10-nm TiO2 nanocrystals into the nanotube arrays. By using the double polymer surfactants of polyethylene glycol and Polyvinyl Pyrrolidone as a sacrificed template, nanocrystal over-agglomeration is prohibited, and thin nanocrystal mesoporous layers are formed on both inner and outer nanotube walls. The application of the nanocrystal filled nanotube arrays as the photoanode for dye-sensitized solar cells has been evaluated. The incorporation of the nanocrystals into the nanotube arrays is found to enhance dye absorption and light-harvesting capacities markedly. As a result, the solar cells based on the filled nanotube arrays hold a short-circuit current density 2.06 times and a power-conversion efficiency 1.94 times higher than those based on the unfilled nanotube arrays.

Tunable plasmon resonance coupling in coaxial gold nanotube arrays

The optical properties and plasmon resonance coupling of double coaxial gold nanotube arrays are investigated. The results show that the optical transmission is highly tunable by varying the thicknesses of the inner and outer nanotubes, the separation between the inner and outer nanotubes, and the dielectric parameters inside, between, and outside the two nanotubes. The shorter-wavelength transmission bands are very sensitive to the modification of the wall thickness of the outer nanotube, the separation, and the dielectric parameters between the double nanotubes. The dipole and multipolar plasmon modes are excited in our model. However, for small separation and refractive index, the dipole normal mode has a leading function in the transmission properties. Compared with the dipolar modes, the contribution of higher-order modes becomes larger as the parameters increase.

Improved performance of flexible dye-sensitized solar cells based on hierarchical TiO2 nanostructures with high surface area

One-dimensional TiO2 nanostructures display remarkable performance in dye-sensitized solar cells by reducing the charge recombination; however, their relatively low surface area restricts both the dye absorption amount and solar energy conversion efficiency. Hydrothermal treatment of anodic TiO2 nanotube arrays in 0.01 M (NH4)2TiF6 increased the surface area of TiO2 photoanodes by generating hierarchical architecture. Hierarchical TiO2 nanostructures obtained by optimal hydrothermal treatment conditions exhibited a wire-in-tube architecture decorated by nanoparticles on both the inner nanowire and the outer nanotube, which further increased the surface area. Flexible dye-sensitized solar cells based on these hierarchical nanostructures yield significantly improved solar energy conversion efficiencies due to enlarged surface area, increased dye loading, and superior light scattering capacity.

Electromagnetic Properties of Inner Double Walled Carbon Nanotubes Investigated by Nuclear Magnetic Resonance

The nuclear magnetic resonance (NMR) analytical technique was used to investigate the double walled carbon nanotubes (DWNTs) electromagnetic properties of inner walls. The local magnetic and electronic properties of inner nanotubes in DWNTs were analyzed using 25% 13C enriched C60 by which the effect of dipolar coupling could be minimized. The diamagnetic shielding was determined due to the ring currents on outer nanotubes in DWNTs. The NMR chemical shift anisotropy (CSA) spectra and spin‐lattice relaxation studies reveal the metallic properties of the inner nanotubes with a signature of the spin‐gap opening below 70 K.

Enhanced electrical properties of composite nanostructures using BiFeO3 nanotubes and ferroelectric copolymers

In this work, composite nanostructures of BiFeO3 (BFO) and poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymers were fabricated using porous anodic aluminum oxide (AAO) templates by sol–gel and vacuum infiltration methods. Scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM) were employed to investigate the morphology of composite nanostructures. It was found that a double-layer nanostructure with inner P(VDF-TrFE) copolymers for high insulating property and outer BFO nanotubes for mechanical supporting. The leakage current density of BFO/P(VDF-TrFE) composite nanostructures is four orders of magnitude lower than that of BFO under ±8MV/m. It is suggested that the facile approach has great potential in multiferroic devices.

Influence of the axial compression on the natural frequency of AFM probes using double-walled carbon nanotubes with different wall lengths

Carbon nanotubes (CNTs) appear to be ideal tip materials of atomic force microscopy (AFM) due to their small diameter and high stiffness. In this study, double-walled carbon nanotube (DWCNT) structures with different lengths of inner and outer layers are proposed as AFM tips. Both the vibration response and mode shapes of the tipped nanotubes under axial compression are studied by a theoretical nanobeam model. The results show that the natural frequencies of DWCNTs are significantly affected by the compressive loads and the length difference between the inner and outer nanotubes. The natural frequency associated with certain vibrational modes decreases with increasing compressive loads. This research may provide a useful reference for practical design for AFM tips with CNTs.

Oxidised multi-wall carbon nanotubes–(R)-polylactide composite with a covalent β-d-uridine filler-matrix linker

Oxidised multi-wall carbon nanotubes (MWCNTs)–(R)-polylactide (PLA) composite was prepared in 85% yield via in-bulk Ring Opening Polymerisation (ROP) of (R,R)-lactide at elevated temperature using a ‘grafting-from’ technique. Outer nanotube walls were firstly covalently functionalised with a β-d-uridine linker—through the more reactive hydroxyl group (5′-OH)—enabling further a direct growth of the polymer from the free secondary hydroxyl groups (2′- and 3′-OH) present in the β-d-ribofuranose moiety. The morphology and chemical structure of the composite were comprehensively studied revealing a high-quality MWCNT-filler dispersion and loading of ca. 7wt%, accompanied by a high molecular weight (Mw) of the (R)-PLA matrix equal to 116,700Da. The presence of nanotube-filler affected the alignment of polymer fibrils in the composite. The elaborated approach may be implemented to a larger scale fabrication of biodegradable composites for medicinal applications or other functional materials where an enhanced matrix-filler interaction is required.

Nonlocal wave propagation in an embedded DWBNNT conveying fluid via strain gradient theory

Abstract Based on the strain gradient and Eringen’s piezoelasticity theories, wave propagation of an embedded double-walled boron nitride nanotube (DWBNNT) conveying fluid is investigated using Euler–Bernoulli beam model. The elastic medium is simulated by the Pasternak foundation. The van der Waals (vdW) forces between the inner and outer nanotubes are taken into account. Since, considering electro-mechanical coupling made the nonlinear motion equations, a numerical procedure is proposed to evaluate the upstream and downstream phase velocities. The results indicate that the effect of nonlinear terms in motion equations on the phase velocity cannot be neglected at lower wave numbers. Furthermore, the effect of fluid-conveying on wave propagation of the DWBNNT is significant at lower wave numbers.

Preparation and characterization of multiferroic CoFe2O4/Bi0.97Ce0.03FeO3 coaxial nanotubes

Multiferroic CoFe2O4 (CFO)/Bi0.97Ce0.03FeO3 (BCFO) coaxial nanotubes were prepared by a sol-gel template method. Transmission electron microscopy revealed that the coaxial nanotubes featured with inner CFO and outer BCFO nanotubes. Selected area electron diffraction confirmed the coexistence of spinel CFO and perovskite BCFO phases in the coaxial nanotubes. Vibrating sample magnetometer measurements showed that the saturated magnetization of the coaxial nanotubes was 3.3 emu/g, smaller than that of CFO nanotubes. The P–E hysteresis loop of the coaxial nanotubes was of poor shape due to possible high conductivity in the inner CFO nanotubes. Dielectric measurements exhibited that the dielectric constant of the coaxial nanotubes decreased while the dielectric loss increased due probably to the small dielectric constant and high conductivity in the inner CFO nanotube. Ferroelectric and magnetic properties were simultaneously demonstrated in the CFO/BCFO coaxial nanotubes.

Charge transfer between carbon nanotubes and sulfuric acid as determined by Raman spectroscopy

The spontaneous interaction between sulfuric acid and carbon nanotubes is studied using Raman spectroscopy. We are able to determine the charge transfer without any additional parameter using the spectral signature of inner and outer walls of double-wall carbon nanotubes. While for the outer wall both the lattice contraction and the nonadiabatic effects contribute to the phonon shift, only the lattice contraction contributes for the inner nanotube. For the outer nanotube, we are able to separate these two contributions of the Raman G-band shift as a function of the charge transfer. We have carried out density functional theory calculations on graphene to see how different chemical species (HSO4 − ,H 2SO4 ,H + ) affect the electronic band structure and electron-phonon coupling. The Raman G-band shift for the outer nanotube, �ω , as a function of hole charge transfer per carbon atom, fC, is found to be �ω (cm −1 ) = (350 ± 20)fC + (101 ± 8) √ fC.

Nonlocal electro-thermal transverse vibration of embedded fluid-conveying DWBNNTs

Electro-thermal transverse vibration of fluid-conveying double-walled boron nitride nanotubes (DWBNNTs) embedded in an elastic medium such as polyvinylidene fluoride (PVDF) which is a piezoelectric polymer is investigated. The elastic medium is simulated as a spring and van der Waals (vdW) forces between inner and outer nanotubes are also taken into account. Zigzag structure of boron nitride nanotubes (BNNTs) is described based on the nonlocal continuum piezoelasticity cylindrical shell theory, and Hamilton’s principle is employed to derive the corresponding higher-order equations of motion. In this model, DWBNNTs are placed in uniform temperature and electric field, the latter being applied through attached electrodes at both ends. Having considered the small scale effect, aspect ratio (L/R), densities of fluid and elastic medium, four different cases of loading are assumed in this study, including: a) direct voltage and heating (DVH), b) direct voltage and cooling (DVC), c) reverse voltage and heating (RVH), and d) reverse voltage and cooling (RVC). Numerical results indicate that increasing nonlocal parameter (e0a), for the four above mentioned cases, decreases the critical flow velocity of fluid. The results could be used in design of nano-electro-mechanical devices for measuring density of a fluid such as blood flowing through such nanotubes with great applications in medical fields.

A Novel Thermal Driving Force for Nanodevices

Design and construction of nanomotors are one of the most attractive fields in nanotechnology. Following the introduction of a novel concept of the thermomass, the relative mass of a phonon gas based on the Einstein’s energy–mass relation, the continuum and momentum conservation equations for the phonon gas are established to characterize the hydrodynamics of the phonon current in a solid. Like the gas flows in the porous mediums, the phonon current in a dielectric solid imposes a driving force on the solid framework atoms, which can be calculated quantitatively and can be applied to actuate nanomotors. We also predict the dynamic behavior of a nanomotor made up of multiwalled carbon nanotubes in terms of molecular dynamics simulations. A shorter single-walled carbon nanotube with a larger diameter, as a mobile part, surrounds a longer single-walled carbon nanotube with a smaller diameter working as a shaft. When a phonon current passes through the inner shaft, the outer nanotube will translate along and/or rotate around the shaft depending on the chiralities of the carbon nanotubes. The motion traces are found to depend on the chirality pair regularly. This type of nanomotor may be promising, because they are directly driven by thermal energy transport.

Thermal properties of nanotubes and nanowires with acoustically stiffened surfaces

A multilayer elasticity model is developed to investigate the effects of acoustically stiffened surfaces (increased surface moduli) on the specific heat and thermal conductivity of typical nanowire and nanotubes as a function of temperature. Changes in phonon dispersion are analyzed using approximated phonon dispersion relations that result from the solutions to the frequency equation of a vibrating elastic tube or rod. The results of the investigation indicate a 10% reduction in specific heat and a 2% decrease in lattice thermal conductivity at 50 K for a 10 nm outer diameter crystalline nanotube with an inner diameter of 5 nm when the average Young’s modulus of the first three atomic layers on both the inner and outer free surfaces are increased by a factor of 1.87. In contrast, a 10 nm outer diameter nanowire composed of the same material and with an acoustically stiffened outer shell shows an approximate 30% increase in thermal conductivity and specific heat near 50 K. Our simplified model can potentially be extended to investigate the acoustic tuning of nanowires and nanotubes by inducing surface stiffening or softening via appropriate surface chemical functionalization protocols or coatings.

Effects of Initial Axial Stress on the Vibration of Double-Walled Carbon Nanotubes under Temperature Field

The paper studies the linear vibrating mechanical behaviors of double-walled carbon nanotubes (DWCNTs) with the initial axial stress under the temperature field. The DWCNTs are modeled as double elastic shells coupled together through vdW interaction between inner and outer nanotubes. Based on the model, the relation between the amplitudes and the frequencies of the tubes is achieved. The results show that the initial axial stress could crucially affect the existence of the natural and intertube frequencies. Meanwhile, it is also concluded that the temperature change is significant for natural frequency, but weakly affects intertube frequency and amplitude ratios.

Electro-thermal non-local vibration analysis of embedded DWBNNTs

In this article, electro-thermal transverse vibration behaviour of double-walled boron nitride nanotubes embedded in a surrounded elastic medium is investigated using non-local piezoelasticity cylindrical shell theory. The effects of the elastic medium including Winkler spring and Pasternak shear constants and van der Waals interaction between inner and outer nanotubes are taken into account. The higher order governing equations of motion are derived based on Hamilton's principle. Effects of parameters such as Winkler spring constant, Pasternak shear constant, electric field, and temperature change on the dimensionless natural frequency are investigated. The results indicate a decrease in the dimensionless natural frequency as both temperature change and electric field are increased for various aspect ratios. However, the decreasing trend is significant for the former and may be considered constant for the latter.

Pasternak foundation effect on the axial and torsional waves propagation in embedded DWCNTs using nonlocal elasticity cylindrical shell theory

The axial and torsional wave propagation in a double-walled carbon nanotube (DWCNT) embedded on elastic foundations are investigated using nonlocal continuum shell theory. The effects of the surrounding elastic medium are considered using the spring constant of the Winkler-type and the shear constant of the Pasternak-type. The van der Waals (vdW) forces between the inner and the outer nanotubes are taken into account. The dynamic response of the carbon nanotube is formulated on the basis of nonlocal elasticity shell theory. The cut-off frequencies are obtained and it has been concluded that the cut-off frequencies are independent of small scale coefficient and shear modulus of the elastic medium. It has been found that the phase velocity sharply decreases by increasing the axial half wave number and approaches a constant value. It has also been concluded that the maximum phase velocity predicted by nonlocal theory is located between 5 and 10 nanometers while for local theories the phase velocity sharply decreases in this interval and approaches a constant value. Results show that the effect of Pasternak-type on phase velocity is significant but the effect of Winkler-type is not really considerable.