Toshiaki Natsuki

Facile Synthesis of BaTiO3 Nanotubes and Their Microwave Absorption Properties

Uniform BaTiO(3) nanotubes were synthesized via a simple wet chemical route at low temperature (50 °C). The as-synthesized BaTiO(3) nanotubes were characterized using powder X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The results show that the BaTiO(3) nanotubes formed a cubic phase with an average diameter of ~10 nm and wall thickness of 3 nm at room temperature. The composition of the mixed solvent (ethanol and deionized water) was a key factor in the formation of these nanotubes; we discuss possible synthetic mechanisms. The microwave absorption properties of the BaTiO(3) nanotubes were studied at microwave frequencies between 0.5 and 15 GHz. The minimum reflection loss of the BaTiO(3) nanotubes/paraffin wax composite (BaTiO(3) nanotubes weight fraction = 70%) reached 21.8 dB (~99.99% absorption) at 15 GHz, and the frequency bandwidth less than -10 dB is from 13.3 to 15 GHz. The excellent absorption property of BaTiO(3) nanotubes at high frequency indicates that these nanotubes could be promising microwave-absorbing materials.

Wave propagation in single- and double-walled carbon nanotubes filled with fluids

Wave propagation approach of single- and double-walled carbon nanotubes conveying fluid is presented through the use of the continuum mechanics. A simplified Flugge shell equations are proposed as the governing equations of motion for carbon nanotubes studied here. For the double-walled nanotubes, the deflection of nested tubes is considered to be coupled through the van der Waals interaction between two adjacent nanotubes. Effects of filled fluid property and nanotube diameter on the wave propagation are investigated and analyzed based on the proposed elastic continuum model. The theoretical investigation may give a useful reference for potential design and application of nanoelectronics and nanodevices.

Analysis of carbon nanotubes on the mechanical properties at atomic scale

This paper aims at developing a mathematic model to characterize the mechanical properties of single-walled carbon nanotubes (SWCNTs). The carbon-carbon (C-C) bonds between two adjacent atoms are modeled as Euler beams. According to the relationship of Tersoff-Brenner force theory and potential energy acting on C-C bonds, material constants of beam element are determined at the atomic scale. Based on the elastic deformation energy and mechanical equilibrium of a unit in graphite sheet, simply form ED equations of calculating Youngs modulus of armchair and zigzag graphite sheets are derived. Following with the geometrical relationship of SWCNTs in cylindrical coordinates and the structure mechanics approach, Youngs modulus and Poissons ratio of armchair and zigzag SWCNTs are also investigated. The results show that the approach to research mechanical properties of SWCNTs is a concise and valid method. We consider that it will be useful technique to progress on this type of investigation.

Vibration analysis of embedded carbon nanotubes using wave propagation approach

A vibration analysis of single- and double-walled carbon nanotubes as well as nanotubes embedded in an elastic matrix is presented using wave propagation approach. Approximate Flugge shell equations are proposed as the governing equations of vibration for the carbon nanotubes studied here. The double-walled nanotubes are assumed to be coupled together through the van der Waals force between the inner and outer nanotubes. For embedded carbon nanotubes, an elastic medium surrounding the nanotubes is described by a Winkler model. Effects of nanotube parameters and vibrational modes on the natural frequency are investigated and analyzed based on the proposed elastic continuum model.

Carbon nanotubes and nanosensors: vibration, buckling and ballistic impact

The main properties that make carbon nanotubes (CNTs) a promising technology for many future applications are: extremely high strength, low mass density, linear elastic behavior, almost perfect geometrical structure, and nanometer scale structure. Also, CNTs can conduct electricity better than copper and transmit heat better than diamonds. Therefore, they are bound to find a wide, and possibly revolutionary use in all fields of engineering. The interest in CNTs and their potential use in a wide range of commercial applications; such as nanoelectronics, quantum wire interconnects, field emission devices, composites, chemical sensors, biosensors, detectors, etc.; have rapidly increased in the last two decades. However, the performance of any CNT-based nanostructure is dependent on the mechanical properties of constituent CNTs. Therefore, it is crucial to know the mechanical behavior of individual CNTs such as their vibration frequencies, buckling loads, and deformations under different loadings. This title is dedicated to the vibration, buckling and impact behavior of CNTs, along with theory for carbon nanosensors, like the Bubnov-Galerkin and the Petrov-Galerkin methods, the Bresse-Timoshenko and the Donnell shell theory.

Composites of multi-walled carbon nanotubes and shape memory polyurethane for electromagnetic interference shielding

Multi-walled carbon nanotubes (MWCNTs) and shape memory polyurethane (SMP) were used to prepare MWCNT/SMP composites for electromagnetic interference (EMI) shielding. The uniform distribution of MWCNTs was confirmed by field emission scanning electron microscopy (SEM). The electrical conductivity of the composites was tested by the four-probe method, and the results suggested that the conductivity of the samples was significantly increased by the presence of MWCNTs. The conductivity reached 35 S/m when the MWCNT loading was 9 wt%. Dynamic mechanical analysis (DMA) revealed that the composites exhibited higher storage moduli than pure SMP. In addition, the shielding effectiveness (SE) of composites with various MWCNT loading and thickness were measured over 4–7 and 13–16 GHz. The highest SE achieved was close to 35 dB for MWCNT/SMP composites with the thickness of 2 mm and MWCNT loading of 9 wt%. The SE increased as the thickness and conductivity of the composites increased. Moreover, the SE was enhanced as the frequency increased.

An atomic-resolution nanomechanical mass sensor based on circular monolayer graphene sheet: Theoretical analysis of vibrational properties

Graphene sheet (GS) is a two-dimensional material with extremely favorable mass sensor properties. In this work, the potential of a nanoscale mass sensor based on individual single layer GS is examined. An atomic-resolution nanomechanical mass sensor is modeled by a fixed supported circular monolayer GS with attached nanoparticles, based on a continuum elastic model and Rayleighs energy method. We analyze the vibrational properties of the GS used as a mass sensor in detail, and the relationship between the attached mass and the vibrational frequency (frequency shift) of the GS is simulated and discussed using the two models. The sensitivity of vibrational frequency (frequency shift) to both aspect ratio and vibration mode is demonstrated, and comparison of the two models proves their accuracy and that of the simulation of the monolayer GS mass sensor.

Vibration analysis of nanomechanical mass sensor using double-layered graphene sheets resonators

Graphene sheets (GSs) are two-dimensional material with extremely favorable mass sensor properties. In the study, we examined the potential of nanoscale mass sensor based on simply supported double-layered graphene sheets (DLGSs) attached nanoparticles. Using the continuum elasticity theory, the influences of the attached mass and position of the nanoparticles on the frequency shifts of DLGSs are investigated in detail. The result shows that the frequency shift in DLGSs is much higher than that of the single-layered graphene sheets (SLGSs). The DLGSs based nanomechanical resonator could provide higher sensitivity than SLGSs.

Electrical Conduction and Percolation Behavior of Carbon Nanotubes/UPR Nanocomposites

The carbon nanotubes (CNT)/unsaturated polyester resin (UPR) nanocomposites are fabricated, and their electrical conduction and percolation behavior are investigated experimentally and theoretically. The carbon nanotubes used in this study are those by the chemical vapor deposition (CVD) method; vapor grown carbon fiber (VGCF) has an average diameter of 150 nm and vapor grown nanofiber (VGNF) has about 80 nm in diameter. The electrical conductivity of the nanocomposites is measured as a function of carbon nanotube volume fraction to understand the percolation behavior. The nanocomposites show the electrical conductivity with low percolation threshold between 2 and 3 vol%. Moreover, the percolation threshold is examined as a function of fiber aspect rate based on simulation calculations. The critical CNT volumes fraction is in good agreement between the theoretical prediction and the experiment results.

Equivalent Young's modulus and thickness of graphene sheets for the continuum mechanical models

The Youngs modulus and the thickness of graphene sheets (GSs) are the two major material constants when continuum mechanical models are used to analyze the mechanical behaviors of GSs. It should be pointed out that the equivalent Youngs modulus and the thickness of GSs should correspond to both stretching and bending loading conditions. In this Letter, the same as “Yakobson paradox,” we predicted the equivalent Youngs modulus and the thickness of GSs using an analytical method linked with an atomic interaction based continuum model and a continuum elastic model. Based on the proposed method, by unifying the Youngs modulus of GSs in the cases of both stretching and bending, and by determining the matching thickness in the same time, the equivalent Youngs modulus and the thickness of GSs utilized in continuum mechanical models are calculated and proposed to be 2.81 TPa and 1.27 A, respectively.