Double-walled Boron Nitride Nanotubes Research Articles

Theoretical investigation on wave propagation in embedded DWBNNT conveying ferrofluid via stress and strain–inertia gradient elasticity

In the present study, wave propagation characteristics of double-walled boron nitride nanotubes (DWBNNTs) conveying ferrofluid is investigated. Magnetite (Fe3O4) nanofluid is selected as a conveying fluid which reacted in presence of magnetic field. Shear effects of surrounded medium are taken into account using Pasternak model. Stress and strain–inertia gradient elasticity theories are used due to their capability to interpret size effect. Based on Hamilton’s principle and employing Euler–Bernoulli, Timoshenko and Reddy beam models, wave equations of motion in double-walled boron nitride nanotubes are derived and solved by harmonic solution. Regarding the various types of flow regimes in fluid–structure interaction, the upstream and downstream phase velocities of double-walled boron nitride nanotubes conveying ferrofluid are calculated. A detailed parametric study is conducted to clarify the influences of the beam models, size effect theories, magnetic field, surrounding elastic medium and fluid velocity on the wave propagation of double-walled boron nitride nanotubes conveying ferrofluid. The results indicated that in lower wave numbers, the effect of flowing fluid and the difference between the upstream and downstream phase velocities were considerable. The results of this work can be used in design and manufacturing of nanopipes and nanovalves conveying fluid flow to avoid water hammer phenomenon.

Molecular dynamics investigation into the oscillatory behavior of double-walled boron-nitride nanotubes

In this paper, the oscillatory behavior of double-walled boron-nitride nanotubes is investigated based on the molecular dynamics (MD) simulations. The MD simulations are performed using the Lennard-Jones and Tersoff-like potential functions. The influences of friction between the walls of inner and outer tubes, flexibility, velocity and outer length-to-inner length ratio on the frequency of oscillations are studied. The results show that the flexibility increases the frequency during the simulation. Furthermore, it is observed that by increasing the initial velocity, the frequency decreases.

Stability characteristics and structural properties of single- and double-walled boron-nitride nanotubes under physical adsorption of Flavin mononucleotide (FMN) in aqueous environment using molecular dynamics simulations

The non-cytotoxic properties of Boron-nitride nanotubes (BNNTs) and the ability of stable interaction with biomolecules make them so promising for biological applications. In this research, molecular dynamics (MD) simulations are performed to investigate the structural properties and stability characteristics of single- and double-walled BNNTs under physical adsorption of Flavin mononucleotide (FMN) in vacuum and aqueous environments. According to the simulation results, gyration radius increases by rising the weight percentage of FMN. Also, the results demonstrate that critical buckling force of functionalized BNNTs increases in vacuum. Moreover, it is observed that by increasing the weight percentage of FMN, critical force of functionalized BNNTs rises. By contrast, critical strain reduces by functionalization of BNNTs in vacuum. Considering the aqueous environment, it is observed that gyration radius and critical buckling force of functionalized BNNTs increase more considerably than those of functionalized BNNTs in vacuum, whereas the critical strains approximately remain unchanged.

A molecular dynamics study on the vibration of carbon and boron nitride double-walled hybrid nanotubes

Synthesis of hybrid nanotubes to overcome the drawbacks of individual pure nanotubes in order to apply them in novel nanodevices has attracted great interest of researchers. To this end, pure single- and double-walled boron nitride nanotubes together with carbon and boron nitride double-walled hybrid nanotubes are simulated through molecular dynamics simulations in order to study their vibrational behavior. The natural frequency of nanotubes is computed, and the effects of geometrical parameters and boundary conditions on the natural frequency are investigated. According to the generated results, the natural frequency of boron nitride nanotubes is higher than that of their carbon counterpart and nanotubes with clamped boundary conditions possess the highest natural frequency compared to other types of boundary conditions. Also, the natural frequency of double-walled hybrid nanotubes is found to be between those of pure double-walled boron nitride and carbon nanotubes with small lengths. It is found that the natural frequency of double-walled hybrid nanotubes is less sensitive to length increase compared to pure double-walled carbon and boron nitride ones, leading to higher frequencies at greater lengths. Finally, to study the variation in natural frequency with the length, a rational curve is fitted to each data set and the corresponding constants are computed.

Raman-Active Modes in Finite and Infinite Double-Walled Boron Nitride Nanotubes

In this theoretical work, we study the Raman spectra of double-walled boron nitride nanotubes (DBNNTs) as a function of their diameters, chiralities, and lengths. Calculations are performed using the spectral moments method coupled to the bond polarizability model. This original approach allows us to consider not only infinite tubes as usual in most theoretical models but also tubes with finite lengths. We provide benchmark theoretical data to estimate the diameter and length of DBNNTs using Raman measurements.

Nonlinear vibration and instability of a visco-Pasternak coupled double-DWBNNTs-reinforced microplate system conveying microflow

The present article deals with the nonlinear vibration and instability analysis of a bonded double-smart composite microplate system (DSCMPS) conveying microflow based on nonlocal piezoelasticity theory. Two microplates are connected together by visco-Pasternak medium and both of them made of poly-vinylidene fluoride reinforced by double walled boron nitride nanotubes (DWBNNTs). Modified Navier–Stokes relation is used to evaluate fluid–microplate interaction considering the effects of bulk viscosity and slip boundary condition. Energy method and Hamilton's principle are employed to derive motion equations with regard to von Kármán geometric nonlinearity. Also, charge equation is used to consider electromechanical coupling. Due to existence of nonlinear terms, the governing equations are solved with the help of the differential quadrature method (DQM). A detailed parametric study is conducted to elucidate the effects of the flow velocity, fluid viscosity, Knudsen number, type of elastic medium, temperature change, small scale, aspect ratio, volume fraction, and orientation angle of the DWBNNTs on the vibration and instability behaviors of the coupled DSCMPS. This study might be helpful for the design of nano-electro-mechanical systems/ micro-electro-mechanical systems.

Molecular dynamics study of the torsional vibration characteristics of boron-nitride nanotubes

Abstract In recent years, synthesizing inorganic nanostructures such as boron nitride nanotubes (BNNTs) has led to extensive studies on their exceptional properties. In this study, the torsional vibration behavior of boron-nitride nanotubes (BNNTs) is explored on the basis of molecular dynamics (MD) simulation. The results show that the torsional frequency is sensitive to geometrical parameters such as length and boundary conditions. The axial vibration is found to be induced by torsional vibration of nanotubes which can cause instability in the nanostructure. It is also observed that the torsional frequency of BNNTs is higher than that of their carbon counterpart. Moreover, the shear modulus is predicted by incorporating MD simulation numerical results into torsional vibration frequency obtained through continuum-based model of tubes. Finally, it is seen that the torsional frequency of double-walled boron-nitride nanotubes (DWBNNTs) is between the frequencies of their constituent inner and outer tubes.

The excitonic effects in single and double-walled boron nitride nanotubes.

The electronic structures and excitonic optical properties of single- and double-walled armchair boron nitride nanotubes (BNNTs) [e.g., (5,5) and (10,10), and (5,5)@(10,10)] are investigated within many-body Green's function and Bethe-Salpeter equation formalism. The first absorption peak of the double-walled nanotube has almost no shift compared with the single-walled (5,5) tube due to the strong optical transition in the double-walled tube that occurs within the inner (5,5) one. Dark and semi-dark excitonic states are detected in the lower energy region, stemming from the charge transfer between inner and outer tubes in the double-walled structure. Most interestingly, the charge transfer makes the electron and the hole reside in different tubes. Moreover, the excited electrons in the double-walled BNNT are able to transfer from the outer tube to the inner one, opposite to that which has been observed in double-walled carbon nanotubes.

Mechanical deformations of boron nitride nanotubes in crossed junctions

We present a study of the mechanical deformations of boron nitride nanotubes (BNNTs) in crossed junctions. The structure and deformation of the crossed tubes in the junction are characterized by using atomic force microscopy. Our results show that the total tube heights are reduced by 20%–33% at the crossed junctions formed by double-walled BNNTs with outer diameters in the range of 2.21–4.67 nm. The measured tube height reduction is found to be in a nearly linear relationship with the summation of the outer diameters of the two tubes forming the junction. The contact force between the two tubes in the junction is estimated based on contact mechanics theories and found to be within the range of 4.2–7.6 nN. The Young's modulus of BNNTs and their binding strengths with the substrate are quantified, based on the deformation profile of the upper tube in the junction, and are found to be 1.07 ± 0.11 TPa and 0.18–0.29 nJ/m, respectively. Finally, we perform finite element simulations on the mechanical deformations of the crossed BNNT junctions. The numerical simulation results are consistent with both the experimental measurements and the analytical analysis. The results reported in this paper contribute to a better understanding of the structural and mechanical properties of BNNTs and to the pursuit of their applications.

Nonlinear vibration of embedded smart composite microtube conveying fluid based on modified couple stress theory

Electro-thermo-mechanical nonlinear vibration and instability of a fluid conveying smart composite microtube made of polyvinylidene fluoride (PVDF) are investigated in this article based on the modified couple stress theory and Timoshenko beam model. The composite matrix is reinforced by double-walled boron nitride nanotubes (BNNTs). Mechanical, electrical, and thermal characteristics of equivalent composite are determined based on micromechanical model. The surrounded elastic medium is taken into account using Winkler and Pasternak models. Considering the small-size effects and slip boundary conditions of microflow through Knudsen number and applying Hamilton's principle, the coupled differential equations, containing displacement and electric potential terms, are obtained. The differential quadrature method is applied to discretize the coupled governing equations and boundary conditions, which are then solved to obtain the nonlinear frequency and critical fluid velocity of the fluid-conveying microtube. The detailed parametric study is conducted, focusing on the combined effects of the Knudsen number, nonlocal parameter, BNNT volume percent, temperature change, elastic medium, and aspect ratio on the nonlinear frequency and critical fluid velocity. Results indicate that the natural frequency and the critical fluid velocity of the smart composite microtube increase with increasing the small-scale parameter. POLYM. COMPOS., 36:1314–1324, 2015. © 2014 Society of Plastics Engineers

Nonlocal surface piezoelasticity theory for dynamic stability of double-walled boron nitride nanotube conveying viscose fluid based on different theories

Based on nonlocal piezoelasticity theory, dynamic stability of double-walled boron nitride nanotubes (DWBNNTs) conveying viscose fluid is studied by incorporating Euler–Bernoulli beam theory, Timoshenko beam theory, and cylindrical shell theory. The surface stress effects are considered based on Gurtin–Murdoch continuum theory. The DWBNNT is embedded in visco-Pasternak medium and the nonlinear van der Waals forces between the inner and outer surface of the DWBNNT is taken into account. Using von Kármán geometric nonlinearity, the governing equations are derived based on Hamilton’s principle. In order to obtain the dynamic instability region of DWBNNT, incremental harmonic balance method is applied. The detailed parametric study is conducted, focusing on the combined effects of the nonlocality, surface stress, fluid velocity, and surrounding medium on the dynamic instability region of DWBNNT. Furthermore, dynamic instability region of Euler–Bernoulli beam theory, Timoshenko beam theory, and cylindrical shell theory are compared to each other. Numerical results indicate that neglecting the surface stress effects, the difference between dynamic instability region of three theories becomes remarkable.

Inter-layer potential for hexagonal boron nitride

A new interlayer force-field for layered hexagonal boron nitride (h-BN) based structures is presented. The force-field contains three terms representing the interlayer attraction due to dispersive interactions, repulsion due to anisotropic overlaps of electron clouds, and monopolar electrostatic interactions. With appropriate parameterization, the potential is able to simultaneously capture well the binding and lateral sliding energies of planar h-BN based dimer systems as well as the interlayer telescoping and rotation of double walled boron-nitride nanotubes of different crystallographic orientations. The new potential thus allows for the accurate and efficient modeling and simulation of large-scale h-BN based layered structures.

Dependence of Geometric and Spectroscopic Properties of Double-Walled Boron Nitride Nanotubes on Interwall Distance

We have used density functional theory (DFT) and time dependent (TD)-DFT to systematically investigate the dependency of the geometric and vibro-electronic properties of zigzag and armchair-type doublewalled boron nitride nanotubes ((0,m)@(0,n) and (m,m) @(n,n)-DWBNNTs) on the interwall distance (ΔR) and the number of unit cells. The results of the calculations showed that their structural stability strongly depends on the interwall distance, but not on the number of unit cells, and the (0,m) @(0,m+9/10) and (m,m) @(n,n) with n=m+5/6 are the most energetically stable structures. The predicted electronic structures for DWBNNTs with cell lengths of one unit exhibit a strong red-shift for the ΔR below ~0.4 nm and remain almost constant for the ΔR > 0.45 nm. The calculated nonresonance Raman spectra of (0,6) @(0,n)-DWBNNTs (with cell lengths of one unit and n=12–18) indicated that the radial breathing modes (RBMs) of inner (0,6) and outer (0,n) tubes are not only diameter dependent, but also exhibit a strong blue-shift for the ΔR below ~0.35 nm and rapidly approach zero with increasing ΔR reference to the position of the RBM in the spectrum of the corresponding single wall boron nitride nanotubes, (0,n)-SWBNNTs. The calculated IR spectra of the (0,6) @(0,n)-DWBNNTs did not indicate any significant dependence on the ΔR for n > 13.

Nonlocal Timoshenko beam model for dynamic stability of double-walled boron nitride nanotubes conveying nanoflow

Based on nonlocal piezoelasticity theory, dynamic stability of double-walled boron nitride nanotube conveying viscous fluid is investigated using Timoshenko beam theory. Double-walled boron nitride nanotube is surrounded in visco-Pasternak medium and conducts the internal fluid. Modified Navier–Stokes relation is used to evaluate fluid–double-walled boron nitride nanotube interaction considering the effects of bulk viscosity and slip boundary condition. Mechanical harmonic excitation and thermal loadings are exerted on double-walled boron nitride nanotube with zero electrical boundary condition. Nonlinear van der Waals forces between the inner and outer layers of double-walled boron nitride nanotube are taken into account. Hamilton’s principle is utilized to derive governing equations with regard to von Kármán geometric nonlinearity. Charge equation is used to consider the coupling of electric potential and mechanical displacement. Space and time domains are discretized using Galerkin and incremental harmonic balance approaches. Finally the eigenvalue equations are solved based on the iterative method to derive dynamic instability regions. The detailed parametric study is conducted, focusing on the combined effects of aspect ratio, nonlocal parameter, fluid velocity, Knudsen number, thermal changes, van der Waals forces and surrounding medium on dynamic instability regions of double-walled boron nitride nanotube.

Electric field effect on the electronic properties of double-walled carbon-doped boron-nitride nanotubes

Carbon (C) doped zigzag (8, 0)@(16, 0) and armchair (5, 5)@(10, 10) double-walled boron-nitride nanotubes (DWBNNTs), under the influence of external electric fields applied in different directions are studied through first-principles calculations. We have considered the substitution of a B and a N (one species at each wall—inner or outer) by C atoms, generating a type-n inside a type-p semiconductor ((type-n)@(type-p)) and vice-versa. The resulting doped DWBNNT can be thought as a p–n junction. The obtained formation energies and structural properties results indicate that these structures present good stability and are not affected by the electric field application. For the electronic structure, it was observed that external fields can be used to modulate these systems energy gaps. Also, there is a preferred field direction which minimizes the gap values, and the gap increase or decrease is related to the reverse and direct polarization of the p–n junction, respectively.

Nonlinear vibration and instability of fluid-conveying DWBNNT embedded in a visco-Pasternak medium using modified couple stress theory

Nonlinear free vibration and instability of fluid-conveying double-walled boron nitride nanotubes (DWBNNTs) embedded in viscoelastic medium are studied in this paper. The effects of the transverse shear deformation and rotary inertia are considered by utilizing the Timoshenko beam theory. The size effect is applied by the modified couple stress theory and considering a material length scale parameter for beam model. The nonlinear effect is considered by the Von Karman type geometric nonlinearity. The electromechanical coupling and charge equation are employed to consider the piezoelectric effect. The surrounding viscoelastic medium is described as the linear visco-Pasternak foundation model characterized by the spring and damper. Hamilton’s principle is used to derive the governing equations and boundary conditions. The differential quadrature method (DQM) is employed to discretize the nonlinear higher-order governing equations, which are then solved by a direct iterative method to obtain the nonlinear vibration frequency and critical fluid velocity of fluid-conveying DWBNNTs with clamped-clamped (C-C) boundary conditions. A detailed parametric study is conducted to elucidate the influences of the small scale coefficient, spring and damping constants of surrounding viscoelastic medium and fluid velocity on the nonlinear free vibration, instability and electric potential distribution of DWBNNTs. This study might be useful for the design and smart control of nano devices.

Electro-thermo-torsional buckling of an embedded armchair DWBNNT using nonlocal shear deformable shell model

Electro-thermo-torsional buckling response of a double-walled boron nitride nanotube (DWBNNT) has been investigated based on nonlocal elasticity and piezoelasticity theories. The effects of surrounding elastic medium such as the spring constant of the Winkler-type and the shear constant of the Pasternak-type are taken into account. The van der Waals (vdW) forces are considered between inner and outer layers of nanotube. According to the relationship between the piezoelectric coefficient of armchair boron nitride nanotubes (BNNTs) and stresses, the first order shear deformation theory (FSDT) is used. Energy method and Hamilton’s principle are employed to obtain coupled differential equations containing displacements, rotations and electric potential terms. The detailed parameter study is conducted to investigate the effects of nonlocal parameter, elastic foundation modulus, temperature change, piezoelectric and dielectric constants on the critical torsional buckling load. Results indicate that the critical buckling load decreases when piezoelectric effect is considered.

Nonlinear vibration and instability of embedded double-walled boron nitride nanotubes based on nonlocal cylindrical shell theory

This paper investigates the nonlinear vibration and instability of the embedded double-walled boron nitride nanotubes (DWBNNTs) conveying viscous fluid based on nonlocal piezoelasticity cylindrical shell theory. The elastic medium is simulated as Winkler–Pasternak foundation, and adjacent layers interactions are assumed to have been coupled by van der Walls (vdW) force evaluated based on the Lennard–Jones model. The nonlinear strain terms based on Donnell’s theory are taken into account. The Hamilton’s principle is employed to obtain coupled differential equations, containing displacement and electric potential terms. Differential quadrature method (DQM) is applied to estimate the nonlinear frequency and critical fluid velocity for clamped supported mechanical and free electric potential boundary conditions at both ends of the DWBNNTs. Results indicated that some parameters including nonlocal parameter, elastic medium’s modulus, aspect ratio and vdW force have significant influence on the vibration and instability of the DWBNNT while the fluid viscosity effect is negligible. In addition, the low aspect ratio should be taken into account for DWBNNT in optimum design of nano/micro devices.

Vibrational and electronic properties of single-walled and double-walled boron nitride nanotubes

We calculated IR, nonresonance Raman spectra and vertical electronic transitions of the zigzag single-walled and double-walled boron nitride nanotubes ((0,n)-SWBNNTs and (0,n)@(0,2n)-DWBNNTs). In the low frequency range below 600cm−1, the calculated Raman spectra of the nanotubes showed that RBMs (radial breathing modes) are strongly diameter-dependent, and in addition the RBMs of the DWBNNTs are blue-shifted reference to their corresponding one in the Raman spectra of the isolated (0,n)-SWBNNTs. In the high frequency range above ∼1200cm−1, two proximate Raman features with symmetries of the A1g (∼1355±10cm−1) and E2g (∼1330±25cm−1) first increase in frequency then approach a constant value of ∼1365 and ∼1356cm−1, respectively, with increasing tubes’ diameter, which is in excellent agreement with experimental observations. The calculated IR spectra exhibited IR features in the range of 1200–1550cm−1 and in mid-frequency region are consistent with experiments. The calculated dipole allowed singlet–singlet and triplet–triplet electronic transitions suggesting a charge transfer process between the outer- and inner-shells of the DWBNNTs as well as, upon irradiation, the possibility of a system that can undergo internal conversion (IC) and intersystem crossing (ISC) processes, besides the photochemical and other photophysical processes.

Infrared-active modes in finite and infinite double-walled boron nitride nanotubes

The calculation of the infrared spectrum of double-walled boron nitride nanotubes (DBNNT's) is performed in the framework of the force constants model, using the spectral moment's method. The calculation of the DBNNT infrared active modes as a function of the diameter and chirality of the inner and outer tubes allows us to derive the diameter dependence of the wave number of the breathing-like modes, intermediate-like modes and tangential-like modes in a large diameter range. In particular, the diameter dependence of the wave numbers of the two radial breathing-like modes resulting from the in-phase and counterphase coupled motions of the totally symmetric radial breathing mode (the so-called RBM) of the inner and outer tubes is discussed. Depending on the relative lengths of the inner and outer tubes, additional modes are evidenced in the RBM region. These modes must be considered in the analysis of the experimental data.