Circular Nanotubes Research Articles

Theory of Spin Waves in a Circular Nanotube Composed of an Easy-Plane Ferromagnet. Consideration of the Dissipation for a Non-metallic External Medium

Theory of Spin Waves in a Circular Nanotube Composed of an Easy-Plane Ferromagnet. Consideration of the Dissipation for a Non-metallic External Medium

Realization of Curved Circular Nanotubes Using In Situ Monitored Self-Assembly.

Curved fluidic channels with a circular cross-section play an important role in biology, chemistry, and medicine. However, in nanofluidics, a problem that is largely unsolved is the lack of an effective fabrication method for curved circular nanotubes (10-1000 nm). In this work, an electron-beam-induced self-assembly process was applied to achieve fine curved nanostructures for the realization of nanofluidic devices. The diameter of the tube could be precisely controlled by an atomic layer deposition process. Fluid transported through the nanochannels was verified and characterized using a dark-field microscope under an optical diffraction limit size. The fluid flow demonstrates that the liquid's evaporation (vapor diffusion) in the nanochannel generates compressed vapor, which pumps the liquid and pushes it forward, resulting in a directional flow behavior in the ∼100 nm radius of tubes. This phenomenon could provide a useful platform for the development of diverse nanofluidic devices.

Optical Sensing of Electron-Beam Position With Twin Silver Nanotube Antenna Tuned to Hybrid Surface Plasmon Resonance

Considered is the diffraction radiation of a flat modulated beam of electrons flowing between two identical circular nanotubes made of silver. The electromagnetic field of such a beam is a two-dimensional H-polarized surface wave, which propagates in the same direction as the beam, with the phase velocity equal to the beam velocity. This field excites the currents on the nanotubes that radiate even if the beam does not touch the scatterers. For numerical solution, we use the method of partial separation of variables and the addition theorems for cylindrical functions that reduces the diffraction radiation problem to a matrix equation. On casting this equation to the Fredholm second-kind form, we compute far-field scattering cross-sections and field patterns with controlled accuracy. The obtained results show that a shift of the beam trajectory from the central-symmetric position triggers the excitation of certain resonances, which are absent otherwise. This may serve as a basis for the design of novel optical-range beam position monitors of nanoscale dimensions.

Static analysis of a circular nanotube made of functionally graded bi-semi-tubes using nonlocal strain gradient theory and a refined shear model

We in this article put forward a novel size-dependent beam model for static bending deformation of a functionally graded bi-semi-tube subjected to different boundary conditions based on the nonlocal strain gradient theory. The tube is formed by bonding together a ZrO2/Ti–6Al–4V functionally graded lower semi-tube and a Si3N4/SUS304 functionally graded upper one. The effective material properties Pf of FG bi-semi-tubes are assumed to vary along the radius of tube. We propose a refined shear model without requiring a shear correction factor for bars with circular cross section. Next the model is used to derive the governing equations of the tube based on the Hamilton's principle. The obtained equations form present a detailed analysis include a nonlocal parameter as well as a material length scale parameter, so much that they can account for the size-dependent in static bending of FG bi-semi-tubes. Later, these equations are resolved analytically by using an improved perturbation method. The analytical solutions are used to discuss the influence of various physical parameters on static mechanical performance of nanotubes, such as double volume fraction indexes, inner radius, the variation of temperature, strain gradient parameter, nonlocal parameter, scale parameter ratio. At last, compared with the conventional approaches, the novel approach is suggested in such work to lead to more accurate bending deformation in the same dimensionless size of tubes.

Diameter-dependent polygonal cross section for holey phenine nanotubes

The cross-sectional shape of the nanotube is a key factor governing fundamental mechanical properties of the nanotube and the nanotube forest. In contrast to most circular nanotubes, in the present work, we demonstrate that the holey phenine nanotubes have polygonal cross sections with diameter-dependent number of sides. The non-circular cross section is attributed to the high twistability of the continuous C–C chains in the phenine nanotube. Consequently, the phenine nanotube forest has a square lattice structure rather than the regular hexagonal lattice of the carbon nanotube forest, resulting in a smooth buckling process under biaxial compression. The buckling pattern of the phenine nanotube forest is highly ordered with the orientation determined by the initial dislocation that frequently appears in the phenine nanotube forest.

The directional motion of nano-objects induced by an inhomogeneous strain field

Recent molecular dynamics simulations have shown that an inhomogeneous strain field in a substrate could drive nano-objects to move on its surface. A theoretical model is established in this paper in order to find the mechanical mechanism from the continuum mechanics point of view, but with the help of atomic interaction potential. The substrate is represented by graphene, and the above nano-object is represented by a graphene flake or a carbon nanotube. Three typically inhomogeneous strain fields are considered, including linear, power and exponential. It was found that a driving force and a couple moment can be induced on the flat flake and the circular nanotube, respectively. Furthermore, both the driving force and the couple moment increase with the increase in strain gradient in the substrate. The size effect of nano-objects and boundary effect on the movement are also investigated in order to explain some interesting results found in the existing numerical simulations. The present theoretical study cannot only reveal the source of the driving mechanism for the movement induced by an inhomogeneous strain field but also give insights for the design of nano-transport devices.

Free vibration analysis of nano-tubes consisted of functionally graded bi-semi-tubes by a two-steps perturbation method

Free vibration of a bimaterial circular nano-tube is investigated. The tube is formed by bonding together a Si3N4/SUS304 functionally graded upper semi tube and a ZrO2/Ti-6Al-4V functionally graded lower semi tube. The material properties of the tube are assumed to vary along the radius according to power law with the power index of upper semi tube differing from that of lower semi tube. Based on non-local elasticity theory and Hamilton’s principle, a refined beam model considering the effect of transverse shear deformation is used to derive the governing equations, then analytical solution is obtained by using a two-steps perturbation method. Our results were compared with the existing ones. The effects on tube’s linear and non-linear frequency are analyzed of the factors, including small scale parameter, temperature, the double volume fraction indexes, slenderness ratio and different types of beam model. A new approach is suggested in this article to change the natural frequency of the tubes by adjusting constituent materials. In contrast to conventional approach, the new one can result in more accurate frequency control in the same dimensionless size of tubes.

Apparent permeability model for real gas transport through shale gas reservoirs considering water distribution characteristic

The accurate knowledge of gas transport mechanisms through shale matrix will significantly advance the development of shale gas reservoirs. At present, the different cross-section shapes for organic and inorganic pores have not drawn much attention. In terms of current literatures, the organic pores are considered as hydrophobic and the inorganic pores is hydrophilic, thus the water film can be adsorbed on the surface of inorganic pore. However, the volume occupied by water film is overlooked and its effect on gas transport capacity has not been investigated ever. In this work, the Beskok’s models are employed, which can be applied to characterize the bulk-gas transport mechanisms through circular nanotubes or slit nanopores with arbitrary aspect ratio. In addition, the organic and inorganic nanopores in shale matrix are assumed as nanotubes and slit nanopores respectively. Considering the presence of adsorbed gas phase, the apparent permeability model for organic pores takes bulk-gas transport regimes, surface diffusion and gas desorption into account. Considering the thickness of adsorbed water film, the apparent permeability model for inorganic matter incorporates the bulk-gas transport mechanisms and effect of water film. More features, such as stress dependence, real gas effect, are included in both models. Based on the proposed permeability models, the influences of pore size, formation pressure, and humidity on apparent permeability for organic/inorganic pores are seriously analyzed. Results show that the surface diffusion will dominate the transport capacity when the organic pore size is less than 2nm. For inorganic pores, it can be concluded that the larger pore radius will obtain the stronger transport capacity. The real gas effect has little influence on apparent gas permeability which can be neglected. The stress dependence, humidity and gas desorption influence the effective radius of nanoscale pores, which have significant effects on transport capacity.

The effects of non-uniform flow velocity on vibrations of single-walled carbon nanotube conveying fluid

The vibrational behavior of a viscous nanoflow-conveying single-walled carbon nanotube (SWCNT) was investigated. The non-uniformity of the flow velocity distribution caused by the viscosity of fluid and the small-size effects on the flow field was considered. Euler-Bernoulli beam model was used to investigate flow-induced vibration of the nanotube, while the non-uniformity of the flow velocity and the small-size effects of the flow field were formulated through Knudsen number (Kn), as a discriminant parameter. For laminar flow in a circular nanotube, the momentum correction factor was developed as a function of Kn. For Kn = 0 (continuum flow), the momentum correction factor was found to be 1.33, which decreases by the increase in Kn may even reach near 1 for the transition flow regime. We observed that for passage of viscous flow through a nanotube with the non-uniform flow velocity, the critical continuum flow velocity for divergence decreased considerably as opposed to those for the uniform flow velocity, while by increasing Kn, the difference between the uniform and non-uniform flow models may be reduced. In the solution part, the differential transformation method (DTM) was used to solve the governing differential equations of motion.

Adjustable transmission properties through ring-shaped nanotube arrays using finite-difference time-domain method

Metallic ring-shaped nanotube arrays are proposed and its optical transmission properties are studied by using finite-difference time-domain (FDTD) method. Compared with the transmission spectra of conventional circular nanotube arrays, two photonic band gaps are emerged in the transmission spectra of ring-shaped nanotube arrays, the two band gaps and transmission spectra are adjusted by the length, inner radius, intertube spacing and the dielectric constants of the core and embedding medium, and magnitude modification, redshift and blueshift of the resonance modes are observed. A metallic ring-shaped nanotube arrays for subwavelength band-stop filter in the range of visible light can be achieved. To understand its physical origin, field-interference mechanism was suggested by the field distributions. The proposed nanostructures and results may have great potential applications in subwavelength near-field optics.

Size and surface effects on the mechanical behavior of nanotubes in first gradient elasticity

First gradient elasticity theory considering surface energy is employed to investigate the axisymmetric deformation of circular nanotubes, in which the microstructural and surface effects are taken into account. The governing equilibrium equation is derived and the corresponding analytical solutions are obtained. It is demonstrated that the total stress decreases with the increase of the intrinsic bulk size, while it increases with the increase of the directional surface energy length parameter. These parameters have strong influences on the mechanical behavior of the embedded nanotubes and thus should be considered in the practical analysis of nanostructures.

Basic amino acid assisted‐fabrication of rectangular nanotube, circular nanotube, and hollow microsphere of polyaniline: Adjusting and controlling effect of pH value

AbstractThis work reports a simple and effective method to prepare polyaniline (PANI) nanotubes with rectangular or circular cross section and hollow microspheres by using basic amino acids L‐lysine or L‐arginine as dopants and pH buffer agents, respectively. The research reveals that the pH value of the reaction solution at the beginning stage is a crucial factor to form PANI microstructures. The L‐lysine and L‐arginine have isoelectric point 9.74 and 10.76, which can maintain reaction solution at high pH value at the beginning reaction and assist aniline to couple in ortho‐position forming phenazine unit in the oligomer chain. The oligomer produces rectangular nanorods or microspheres by interaction. These oligomer microstructures act as templates for further polymerization to form PANI rectangular nanotubes and hollow microspheres. Decreasing the concentration of the basic amino acid or using acidic amino acid, the round nanotubes are formed. This method provides a simple route to prepare PANI microstructures with different morphologies without any foreign template or surfactant, and raises a new view on the polymerization process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Chiral tunneling in metallic carbon nanotubes

The concept of chiral tunneling in metallic single-wall carbon nanotubes, originating from the interplay of local electrostatic and pseudomagnetic potentials, is considered and applied to an evaluation of the Josephson current in a nanotube-based superconductor--normal metal--superconductor (SNS) junction and the persistent current in a circular nanotube. In the former case, an oscillatory dependence of the critical supercurrent on the potential strength and the nanotube chiral angle is predicted. In the latter case, the existence of a spontaneous persistent current in an isolated ringlike nanotube is discussed.

Chiral effects in normal and superconducting carbon nanotube-based nanostructures

The novel phenomenon of chiral tunneling in metallic single-wall carbon nanotubes is considered. It is induced by the interplay of electrostatic and pseudomagnetic effects in electron scattering in chiral nanotubes and is characterized by an oscillatory dependence of the electron transmission probability on the nanotube chiral angle and the strength of the scattering potential. The appearance of a special (Aharonov–Bohm-like) phase in chiral tunneling affects various phase-coherent phenomena in nanostructures. We examine chiral effects in: (i) persistent currents in circular nanotubes, (ii) Josephson currents in nanotube-based SNS junctions, and (iii) resonant electron tunneling through chiral nanotube-based quantum dots.

Oscillatory Gas Flow in a Circular Nanotube

Gas flow through nanoscale conduits shows distinctly different physics compared to flow at the macroscale. One of the first manifestations of this is the appearance of wall slip. Here we consider the oscillatory flow of an incom- pressible Newtonian gas through a circular nanotube, with first order wall slip due to rarefaction. It was found that the ma- jor effect of wall slip at lower oscillation frequencies is to alter the instantaneous velocity profiles from Poiseuille-like to more plug-like, with an overall enhancement to the fluid velocity magnitude. However, at higher frequencies the en- hancement to velocity magnitude due to wall slip is greatly diminished, and rarefaction introduces a region of backflow near the centerline of the nanotube. These flow characteristics may have important implications for the design of various practical applications of unsteady gas flow through nanoscale conduits, from fuel cell membranes to gas-powered nanomachines constructed from carbon nanotubes.

Oscillatory Gas Flow in a Circular Nanotube

Oscillatory Gas Flow in a Circular Nanotube

Study of Carbon Nanotubes Under High Pressure

ABSTRACTThe elastic behavior and structural changes of single-walled carbon nanotubes under hydrostatic pressure produced by a gasketed diamond anvil cell has been studied using in situ synchrotron x-ray diffraction. The compaction of the raft-like bundles of single-walled carbon nanotube showed a linear behavior up to 1.5 GPa pressure and the volume compressibility deduced from the experimental data is 0.024 GPa−1. The elastic deformation is attributed to the combination of a reduction in the inter-tubular distance and the polygonization of the otherwise circular nanotube sections.