Photonic crystals and fractals with three-dimensional dielectric structures were fabricated in order to control millimeter waves effectively by using micro-stereolithography of rapid prototyping. The photonic crystals with a diamond structure composed of alumina lattice were fabricated. The micrometer order periodic structures exhibit perfect band gaps in terahertz frequency range. The photonic fractals with the self-similar structure of dielectric medium can localize electromagnetic wave energy. Menger-sponge fractal structures composed of alumina were also fabricated. In the micro-sterereolithography process, the photo sensitive resin paste with nanosized alumina particles dispersion was spread on a substrate with 10 μm in layer thickness by moving a knife edge, and two-dimensional images of UV ray were exposed by using DMD （Digital Micro-mirror Device） with 2 μm in part accuracy. Through the layer by layer stacking process, micrometer order three-dimensional structures were formed. Dense alumina structures were obtained by dewaxing and successive sintering in an air atmosphere. The electromagnetic wave properties of these samples were measured by using a terahertz spectroscopy device. The propagation and localization behavior of THz waves in photonic crystals and fractals composed of alumina will be reported. In near future, millimeter wave in a terahertz frequency range will be expected to apply for various types of novel sensors which can detect gun powders, drugs, bacteria in foods, micro cracks in electric devices, cancer cells in human skin and other physical, chemical and living events. To control millimeter waves in terahertz frequency range, micrometer order electromagnetic devices of photonic crystals and fractals for cavities, filters and antennas would be used.
Recently, many nonviral vectors modified with cationic lipids, cationic polymers, etc. for facilitating gene therapy have been reported. However, those nonviral vectors with cationic materials require improved stability, longer duration of gene expression, and reduced cytotoxicity. We found that nucleic acid, which was not dispersed in the organic solvent, could be dispersed by forming a complex with cationic lipid. Using this phenomenon, polynucleic acids for gene therapy （plasmid DNA, antisense oligonucleotide, small interfering RNA, etc.） can be encapsulated into the matrix of the biodegradable polymer particles which is poly-lactic-glycolic acid （PLGA） with the emulsion solvent diffusion method. The advantages of this preparation method are its simple process and avoidance of an ultrasonication process for submicronization of particles. Furthermore, by modification of nanoparticulate surface by chitosan or TweenR 80 （polysorbate 80）, the nanospheres show better cellular uptake and different gene therapeutic effects compared with conventional vectors due to their improved adherence to cells and sustained release of polynucleic acid in the cells. In conclusion, surface modified PLGA nanospheres can possibly be applied in nonviral vectors for gene therapy.
Synthesis of zeolite membrane was examined by the supercritical extraction method that is the template of zeolite being extracted with supercritical methanol and carbon dioxide mixtures. At first, ZSM-5 particles were synthesized with supercritical extraction method. The shape of zeolite particles remained itself after the supercritical extraction with methanol-carbon dioxide mixtures, whereas the particle was broken after the supercritical methanol only. The template was extracted above 250 ℃ with supercritical methanol-carbon dioxide mixture while no template was extracted with supercritical carbon dioxide carbon dioxide only, which means that the extraction of template was promoted with polar solvent such as methanol in addition to carbon dioxide. Next, ZSM-5/Silicalite composite membrane was synthesized by the supercritical extraction method with methanol-carbon dioxide mixtures. The hydrogen permeated through the membrane whose extraction temperature was above 200 ℃. The increase in extraction temperature increased the permeance. The permeance was significantly lower than the membrane obtained with calcinations of template. Further, the permeance of n-butane and isobutene for the membrane obtained with supercritical extraction method was different from those obtained with calcination of template. The supercritical extraction method for zeolite membrane achieved the formation of membrane containing a lot of template and this membrane shows distinctive properties such as permeance which was different from the membrane obtained with calcination of template.
In this work, dewetting of inorganic nanoparticles/polymer composite thin films, which are notable materials in various fields, has been investigated experimentally. Here, CeO2 nanoparticles surface-modified with oleic acid and polystyrene （PS） were used as nanoparticles and polymer, respectively. The CeO2 nanoparticles were synthesized by organic-ligand-assisted supercritical hydrothermal synthesis by Adschiri et al., and consequently, can be sufficiently dispersed in organic solvent and polymers. In experiment, a PS thin film with CeO2 nanoparticles spun-coated onto a silicon substrate was heated at 393 K, and then dewetting phenomena of the thin film was observed using an optical microscope. As a result, the dewetting was suppressed by adding 0.4 wt ％ CeO2 nanoparticles with respect to PS, and was perfectly inhibited with 1 wt％ CeO2 nanoparticles. However, addition of 5 wt％ nanoparticles causes reoccurrence of dewetting in PS thin films. The interaction energy of polymer thin films with and without nanoparticles was estimated to consider the reason of inhibition of dewetting in the polymer thin film with nanoparticles.
BaTiO3-（Bi1/2Na1/2）TiO3 （BT-BNT） positive temperature coefficient of resistivity （PTC） ceramics were successfully prepared by a wet-chemistry route. With 2 mol％ BNT addition, the obtained BT-BNT ceramics had semiconductivity and exhibited a PTC behavior at about 155℃ . The onset temperature of the PTC effect increased to 165℃ for the 4 mol％ BNT added samples. Room-temperature resistivity rRT increased with the content of BNT added and the ceramics changed from a semiconductor to an insulator, which was consistent with the variation of the microstructure. The temperature of resistivity anomaly in BT-BNT ceramics also increased with increasing BNT content. A small amount of manganese （Mn） dopant was found to improve the PTCR effect in the BT-BNT system. The possible mechanism underlying the PTCR effect in BTBNT ceramics was proposed. We also observed PTC effect on the ceramics sintered in a N2 flow with low O2 concentration. With the addition of BNT, the samples exhibit resistivity jumps of 103-105 starting at 190-210℃. X-ray diffraction results indicate that the BNT phase and BT phase formed a solid solution during sintering. An electrically heterogeneous structure, consisting of the grain interiors, outer grain shells, and grain boundaries, is revealed by the complex impedance analyses. The observed dc resistivity jump is attributed to the rapid resistivity rise in both grain boundaries and grain shells.
A geometrical model has been developed to optimize the microstructure of porous composite anode electrodes of solid oxide fuel cells. The model takes into account the coordination number theory applied to a random packing of binary particle mixture, together with the percolation theory introduced to provide percolation paths for electrons and ions. The predictions confirm that the effective triple-phase-boundary（TPB） index deduced from a geometric analysis depends on the pore size as well as the characteristic parameters including particle radius ratio, contact angle and composition ratio. The influence of pore size on the effective TPB index is particularly conspicuous, suggesting that the pore size optimization should improve the effective TPB index significantly. The model has also been applied to estimate polarization performance of Ni/YSZ anode electrode, taking into account the electrochemical reaction according to the Butler-Volmer equation along the TPB active sites as well as electronic, ionic, and gas transport phenomena. The calculations confirm that the polarization distribution along the anode becomes uniform with an increase in the anode thickness when the electric/ionic particle size ratio is unity. When the anode thickness is larger than is required, a large part of the electrode does not supply any electrical current. When the anode thickness is smaller than 20μm, in contrast, the result of partial hydrogen pressure distribution indicates that neglecting the mass transfer phenomena in the anode micro-pores would provide an analytical solution of the Butler-Volmer form.
Effect of flow behavior in a honeycomb rectangular tube of a de-NOx catalyst on the adhesion of particles to the wall is studied in terms of a direct numerical simulation（DNS）. The results show that the adhesion of particles to the wall is strongly affected by the turbulent-laminar- transition flow behavior and is enhanced by the turbulence in the upstream region near the inlet. This agrees well with the previous experimental observation, in which the degradation of the catalyst appeared in the region near the inlet. The adhesion of particles is found to be enhanced not only by the stronger turbulence but also by the larger particles. In the downstream region, the adhesion on the wall near the rectangular edges is suppressed, since the turbulent-laminar transition progresses from these regions.
Freezing of a fluid in small pores is a common phenomenon often seen in a natural environment. Water remains in a liquid phase even below 0 Celsius when contained in a fine soil and freezes into ice at lower temperatures. However, this is sometimes a very complicated phenomenon and consists of several slow processes other than crystallization, such as a viscous fluid flow in pores and diffusion of latent heat. These hide inherent features of the crystallization in a quenched disorder by introduced by pores. Using low temperature 4He in the superfluid and the solid phases causes the flow in the pores to be fast enough to reveal the nature of crystallization dynamics. As a porous material for the experiment we use silica-aerogels. Aerogel consists of silica beads in a few nm size. Aerogel has a very large open volume and its porosity is very high, ranging from 90 to 99.5％ in volume. It introduces a quenched disorder to the phase transition of 4He within it. We can alter the strength of the disorder broadly by choosing the porosity of the aerogel. Aerogel is very transparent with a low dielectric constant and suitable for visualizing the dynamics within it. Here we report a novel dynamical transition of the crystallization of 4He in pores. The crystal-superfluid interface advances via creep at high temperatures and via avalanches at low temperatures. The transition temperature is higher at a higher interface velocity and lower in higher porosity aerogels. The transition is due to competition between thermal fluctuations and disorder for the crystallization process.
Layered calcium phenyl phosphate (Ca(C6H5PO4)0.92(HPO4)0.08Ca・1.3H2O: CaPP), which is composed of a multilayer alternating bimolecular layer of phenyl groups and amorphous calcium phosphate phase, was treated in aqueous media including an enzyme such as alkaline phosphatase (ALP) at pH ＝9.6 and 37℃ for 1 - 48 h. The CaPP was transformed into amorphous calcium phosphate with the same Ca/P molar ratio of calcium hydroxyapatite (Ca10(PO4)6(OH)2: Hap) by treating for 1 h. The formed amorphous material possessed no phenyl groups. Furthermore, the plate-like CaPP particles were vanished and the rod-like particles due to amorphous calcium phosphate with ca. 43nm in length and ca. 8nm in width were generated. These facts suggested that all the phenyl phosphates in CaPP were hydrolyzed to generate inorganic phosphate species such as PO43-. The low crystalline Hap nano-particles with irregular shape were produced at 3 h. Then, the molar ratio Ca/P of the product was 1.68, almost corresponding to 1.67 of the theoretical ratio of Hap. The crystallinity of Hap was increased by elongating the treating period up to 6 h and then almost constant. The yielded Hap was rod-like particles with ca. 100nm in length and ca. 10nm in width. On the other hand, when the CaPP particles were treated in aqueous media in the absence of ALP, the CaPP was dissolved and the formation of Hap was not recognized. From these results, it can be presumed that the layered CaPP was dissolved, hydrolyzed and recrystallized to Hap nano-particles by using the ALP. This phase transformation of CaPP in Hap with ALP resembled to the formation mechanism of Hap in animal organism.
MAGIC (MAGnetic Intelligent Compound) is a solidified magnetorheological fluid containing both magnetic particles and nonmagnetic abrasive particles of micron size. In order to produce the effective MAGIC abrasive for polishing, it is important to know how abrasive particles distribute in MAGIC fluids under applied magnetic field. The influences of the volume fractions of particles, diameter ratio of abrasive particles to magnetic particles and shape of magnetic particles on the microstructure formation of particles in MAGIC are examined. In our study, numerical simulations of the particle method are performed to investigate micro-scale structure of particles in MAGIC. In this report, we show the effects of diameter ratio of abrasive particles to that of magnetic particles on the microstructure formation. As the magnetic particles form chain clusters, the abrasive particles are rearranged in the field direction. In order to arrange nonmagnetic particles in the magnetic field direction, the diameter of nonmagnetic abrasive particles should be slightly smaller than the diameter of magnetic particles.
In order to develop dust collecting technique in a vacuum vessel, characteristics of thermal creep flow is numerically evaluated by DSMC method first. The results clarify both creeping velocity profiles on a plane wall with temperature gradient and the optimum regime of Kn number for the dust collection. As the second step, dust collecting experiments under vacuum conditions are performed to verify the numerical predictions, and the some developments needed for the dust collection are suggested, including the prediction of drag forces acting on a spherical particle in a rarefied gas by using the velocity profiles obtained by the numerical simulation.
Boron nitride（BN）nanocapsules encaging Fe or Co nanoparticles were synthesized by using Fe4N/B or Co（NH3）6Cl3/KBH4 powders as raw materials, respectively. The Fe4N was reduced to a-Fe during annealing at 1000 ℃ for several hours with flowing 100 sccm N2 gas, and the reaction was predicted by Ellingham diagram. Co nanoparticles with BN layers were also produced by annealing the powders at 1000 ℃ in nitrogen atmosphere. These BN nanocapsules with magnetic nanoparticles exhibited soft magnetic characteristics and good oxidation resistance.
BN nanotubes, nanohorns and nanocoils were also synthesized by annealing Fe4N and B powders. Especially, Fe-filled BN nanotubes, bamboo-type and cup-stacked type BN nanotubes were produced. Formation mechanism and nanostructures were investigated by high-resolution electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, electron diffraction, energy dispersive X-ray spectroscopy and molecular mechanics calculations.
The nanoparticles of solid solutions between Y3Al5O12 （YAG） and Gd3Al5O12 （GAG） are synthesized from yttrium acetate tetrahydrate, gadolinium acetate tetrahydrate and aluminum isopropoxide at different Y/Gd atomic ratios in 1,4-butanediol by autoclave treatment at 300℃ for 2 h, i.e., by the glycothermal reaction. On the other hand, Yb3+ doped Y3Al5O12 （YAG:Yb3+） nanoparticles are prepared from yttrium acetate tetrahydrate, ytterbium acetate tetrahydrate and aluminum isopropoxide in 1,4-butanediol by autoclave treatment at 300℃ for 2 h. Moreover, Gd-YAG and Gd-YAG:Yb3+ nanoparticles are prepared from the mixture of gadolinium acetate tetrahydrate and either YAG or YAG:Yb3+ colloidal solution by the same autoclave treatment as YAG:Yb3+. Properties of structure, near infrared photoluminescence and magnetic resonance contrast enhancement are characterized for as-prepared nanoparticles. The solid solutions between YAG and GAG work as T2 contrast agent for magnetic resonance imaging, while Gd-YAG works as T1 and T2 contrast agents. Gd-YAG:Yb3+ nanoparticles work as T1 and T2 contrast agents like Gd-YAG nanoparticles, and show near infrared emission at 1030 nm due to the f-f transition of Yb3+ under the 940 nm excitation using near infrared laser diode.
Recent advance in biotechnology enables us to find the peptides with the affinity for nonbiological materials and with the function of mineralizing inorganic materials. The use of the functional peptides is attracting a growing interest for bottom-up fabrication approaches of nanoscale devise. Zinc oxide （ZnO）, a semiconductor with a wide direct band gap, possess unique optical, acoustic, and electronic properties, so that it is one of most widely studied metal oxides for solar cells, sensors, ultra violet nanolaser, blue light-emitting diode and so on. This wide variety of applications requires various fabrications of morphologically and functionally distinct ZnO nanostructures. In this report, we describe the immobilization of ZnO using an artificial peptide with affinity for ZnO at room temperature, and further, we showed, using ZnO-binding peptide and ant-PHB antibody fragments, that strong spontaneous immobilization using biomolecular recognition enabled stepwise stacking of inorganic particles on PHB-coated plates only by mixing operation in neutral solutions at room temperature. We show the potential of recombinant anti-material peptides and antibody fragments for the bottom-up stacking procedures using Inkjet patterning.
Grain refinement is well known to influence the mechanical properties of materials, especially the strength characteristics. The promising method for grain refinement is a SPD process and it produces the homogenized nano grain material which exhibits very high strength and limited ductility. Recently the grain refinement technique by the SPD in powder metallurgy（PM） field has received much attention. The SPD-PM process is one of new processes combining mechanical milling （MM） or alloying （MA）, heat treatment and sintering processes. Microstructure of the SPD-PM materials is easily controlled by the MM condition, and hence we can intentionally make a heterogeneous microstructure. In the present study, SUS316L stainless steel, commercially pure titanium and pure copper powders are applied to the SPD-PM process. These MM powders are sintered by Hot Roll Sintering （HRS）, and the SPD-PM materials demonstrate a heterogeneous microstructure and high strength and advanced plastic strain. The microstructure of materials consists of a shell and core hybrid microstructure, that is, a shell structure with nano grains and a core structure with work-hardened coarse grains. In case of the SUS316L stainless steel, the shell area has an （austenite + sigma） nano duplex structure and the core area in the work-hardened structure has an austenite phase. All of the materials fabricated by these processes demonstrate not only superior strength but also enough elongation. The mechanical properties are strongly influenced by the shell / core microstructure. The nano / meso hybrid microstructure by these processes has been proved to be very effective to improve mechanical properties.
Positively charged calcium hydroxyapatite [Ca10(PO4)6(OH)2 ; Hap] nano-crystals were prepared by using β-alanine and clarified the adsorption affinity of these surface amide functionalized Hap nanocrystals to proteins. Colloidal surface amide functionalized Hap nano-crystals were prepared by wet method in the presence of various amounts of β-alanine by changing molar ratio of β-alanine/Ca (β/Ca ratio) in the solution. The rod-like nano-crystals were lengthened with addition of β-alanine though their width did not vary; carboxyl groups of β-alanine are strongly coordinated to Ca2+ ions exposed on ac and/or bc faces to inhibit particle growth to a- and/or β-axis directions and enhance the particle growth along to the c-axis. No difference can be recognized on the crystal structure among the synthesized Hap nano-crystals by XRD measurements. However, the large difference was recognized by TG-DTA and FTIR measurements. Those measurements reveled that β-alanine is incorporated on the β-alanine-Hap nano-crystal surface up to the β/Ca ratio of 1.0, though they are absent in the nano-crystals synthesized at β/Ca ratio>－2.0. The zeta potential (ZP) of β-alanine-Hap nano-crystals prepared at β/Ca =0.4 and 1.0 of those incorporating β-alanine exhibited positive charge at pH<－5.9. The saturated amounts of adsorbed BSA for the positively charged β-alanine-Hap nano-crystals were increased 2.3～2.4-fold by their electrostatic attraction force between positively charged β-alanine-Hap nano-crystals and negatively charged BSA molecules. We were able to control the adsorption affinity of Hap nano-crystal by changing their surface charge.