Tadafumi Adschiri

Tohoku University, Japan

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Publications (204)480.55 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The thermal dewetting of polystyrene composite thin films with oleic acid-modified CeO2 nanoparticles prepared by the supercritical hydrothermal synthesis method was investigated, varying the nanoparticle concentration (0-30 wt %), film thickness (approximately 50 and 100 nm), and surface energy of silanized silicon substrates on which the composite films were coated. The dewetting behavior of the composite thin films during thermal annealing was observed by an optical microscope. The presence of nanoparticles in the films affected the morphology of dewetting holes, and moreover suppressed the dewetting itself when the concentration was relatively high. It was revealed that there was a critical value of the surface energy of the substrate at which the dewetting occurred. In addition, the spatial distributions of nanoparticles in the composite thin films before thermal annealing were investigated using AFM and TEM. As a result, we found that most of nanoparticles segregated to the surface of the film, and that such distributions of nanoparticles contribute to the stabilization of the films, by calculating the interfacial potential of the films with nanoparticles.
    Langmuir : the ACS journal of surfaces and colloids. 07/2014;
  • Gimyeong Seong, Tadafumi Adschiri
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    ABSTRACT: Highly crystalline cobalt nanoparticles with low surface oxidation were synthesized by the reductive supercritical hydrothermal process in the temperature range from 340 to 420 °C. Under these reaction conditions, hydrogen generated from formic acid decomposition is maximally soluble in water, enabling the effective reduction of cobalt ions and cobalt oxide. The reaction mechanism was investigated by kinetic analysis on the formation of cobalt nanoparticles. This analysis assumed the first order irreversible reaction and two different types of shrinking core models (chemical reaction and inter-diffusion dominated). According to the proposed reaction mechanism, cobalt monoxide is probably formed at the early reaction stage, where insufficient H2 is available, or under high temperature conditions. Moreover, cobalt monoxide influences the entire reaction rate. Thus, suppressing the formation and growth of cobalt monoxide is of primary importance in the optimal synthesis of cobalt nanoparticles by the reductive supercritical hydrothermal process.
    Dalton transactions (Cambridge, England : 2003). 05/2014;
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    ABSTRACT: Gliding of microtubule filaments on surfaces coated with the motor protein kinesin has potential applications for nano-scale devices. The ability to guide the gliding direction in three dimensions allows the fabrication of tracks of arbitrary geometry in space. Here, we achieve this by using kinesin-coated glass wires of micrometer diameter range. Unlike previous methods in which the guiding tracks are fixed on flat two-dimensional surfaces, the flexibility of glass wires in shape and size facilitates building in-vitro devices that have deformable tracks.
    Biomedical Microdevices 04/2014; · 2.72 Impact Factor
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    ABSTRACT: As a complementary tool to nanofluidics, biomolecular based transport is envisioned for nanotechnological devices. We report a new method for guiding microtubule shuttles on multi-walled carbon nanotube tracks, aligned by dielectrophoresis on a functionalized surface. In the absence of electric field and in fluid flow, alignment is maintained. The directed translocation of kinesin propelled microtubules has been investigated using fluorescence microscopy. To our knowledge, this is the first demonstration of microtubules gliding along carbon nanotubes.
    Nano Letters 01/2014; · 13.03 Impact Factor
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    ABSTRACT: Abstract
    01/2014: pages 99-110; , ISBN: 9780444626967
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    ABSTRACT: We report on the crystallographic structure and magnetism of 5-nm Co–Al–O spinel nanocrystals synthesized under supercritical hydrothermal conditions. Structural examination using powder X-ray diffraction and chemical analysis showed the composition of the sample to be Co0.47Al2.36O4 rather than the stoichiometric composition of CoAl2O4 . The site occupancy of Co on the A-site forming the diamond lattice was 0.47, which is slightly larger than the site percolation limit. Magnetization measurements showed that magnetic clusters emerged below 40 K. At temperatures below 40 K, a Griffiths-phase-like inhomogeneous state appeared in the sample in which magnetic clusters and paramagnetic spins coexisted. The dc-paramagnetic and ac-susceptibilities exhibited an anomaly below 7 K.
    Journal of Magnetism and Magnetic Materials 01/2014; 350:161-166. · 1.83 Impact Factor
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    ABSTRACT: A series of gadolinium hydroxide [Gd(OH)3] nanoclusters having different morphologies was synthesized in the presence of 3,4-dihydroxy hydrocinnamic acid (DHCA), an organic modifier, under subcritical water conditions. These well-shaped Gd(OH)3 clusters are composed of many nanorods in a parallel orientation, rather than a disordered aggregation of nanorods, which are linked together by organic DHCA molecules. Here DHCA works as an inter-linker to form these cluster-like structures through coordination bonds. All samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and SQUID magnetometry. We investigated the effect of the concentrations of DHCA and KOH on the size and morphology of the Gd(OH)3 clusters. Their possible formation mechanism is also briefly discussed.
    Dalton Transactions 12/2013; 42(45):16176-16184. · 3.81 Impact Factor
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    ABSTRACT: We have visualized the distributions of temperature and water density in a tubular flow reactor for supercritical hydrothermal synthesis of nanoparticles by neutron radiography, and investigated the effect of reactor configuration on the mixing behavior in the reactor. Here, three types of reactors were used, and the mixing behaviors of supercritical water and room-temperature water at a T-junction in the reactors were observed. As a result, it was revealed that the distributions of temperature and water density in the tubular flow reactors strongly depend on their configurations by neutron radiography. In addition, numerical simulations have been carried out to investigate the flow patterns and temperature distributions in the reactor in detail using the commercial software FLUENT, and it was demonstrated that the numerical results can explain the experimental results obtained by neutron radiography well. © 2013 American Institute of Chemical Engineers AIChE J, 2013
    AIChE Journal 12/2013; · 2.49 Impact Factor
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    ABSTRACT: Simulation of polymerization-induced phase separation of a polymer gel from a multifunctional monomer was carried out using the phase field method. To describe the driving force for phase separation, the interfacial energy between the polymeric phase and the aqueous phase was assumed to depend positively on the degree of polymerization, while the thickness of the interface at equilibrium and the mobility were assumed to depend negatively on it. The mobility was also assumed to depend negatively on the volume fraction of the polymer. A sigmoidal function was introduced to describe the nonlinear dependence of the mobility on the volume fraction. The wavelength of phase separation became finer as the polymerization rate increased when the rate of the reaction had a time scale similar to that of diffusion. When a nonreactive polymer coexists in the phase separation, the wavelength of phase separation shrinks because of suppression of diffusion caused by the coexisting polymer. These results qualitatively agreed with the experimental results for macroporous silica prepared via polymerization-induced phase separation.
    Journal of chemical engineering of Japan 10/2013; 46(10):709-715. · 0.62 Impact Factor
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    Daisuke Hojo, T.Togashi, T. Adschiri
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    ABSTRACT: Uniform and highly ordered nanocrystalline multilayers were obtained after tetrahydrofuran annealing of pre-assembled nanocrystals on the substrate surfaces. As a result of the rearrangement process during solvent annealing, cerium oxide hybrid nanocrystals were correctly positioned in the nanocrystalline film layers because of high carrier ability and the high affinity of the solvent to the nanocrystals. It was also found that solvent annealing had almost no effect on the nanocrystalline monolayer macroscopically, indicating that nanocrystals chemisorbed on the modified substrate surface did not move freely as compared with nanocrystals on top of the pre-assembled nanocrystals. A sufficiently highly ordered nanocrystalline structure was self-assembled in the concentrated solvent and thus printed to such a sticky surface from a face-down configuration that prevented the random deposition of nanocrystals, resulting in the uniform and ordered nanocrystalline monolayer of macroscopic size.
    Japanese Journal of Applied Physics 10/2013; 52:110113. · 1.07 Impact Factor
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    ABSTRACT: Catalytic cracking of Canadian oil sand bitumen in supercritical water was performed to clarify the effect of CeO 2 nanoparticles. The cracking was performed at 723 K to promote a redox reaction between the water, bitumen, and catalyst for the production of hydrogen and oxygen. As the catalyst, CeO 2 with two different morphologies was employed because the redox reaction of CeO 2 with water and organics is expected and its activity can be controlled by its structure. In this study, two roles of water were considered as well. Water is attractive as a high potential medium with low dielectric constant and density at near the critical point (374 °C, 22.1 MPa) that allows formation of highly crystalline smaller metal oxides particles. However, the chemical effects of water are investigated with heavy oil catalytic cracking. Transmission electron microscopy images indicated that CeO 2 nanoparticles with cubic and octahedral shape were synthesized using a plug-flow reactor under hydrothermal conditions. The particles sizes were 8 and 50 nm for cubic and octahedral CeO 2 , respectively. At 773 K, it was found that the oxygen storage capacity (OSC) of the cerium oxide nanoparticles with cubic {100} facets was nearly 3.4 times higher than that of the cerium oxide nanoparticles with octahedral {111} facets. Heavy oil fractions of bitumen were cracked in a batch-type reactor at 723 K in order to produce as much light oil as possible, and the effect of the catalyst loading and reaction conditions on the conversion rate and coke formation were investigated. As a result, it was demonstrated that it is possible to obtain a high conversion rate by increasing the exposed surface area and reducing the particle size of the catalyst. The highest conversion was obtained in the presence of 20 mg loading of cubic CeO 2 nanoparticles (8 nm) with reaction time of 1 h.
    Energy & Fuels 08/2013; 27(8):4624-4631. · 2.85 Impact Factor
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    ABSTRACT: The kinesin motor protein is one of the major contributors in cell division and intracellular transportation of cargo. Kinesin converts chemical energy into mechanical work with a yield greater than 50% and it can transport large size cargo along several micrometers, moving on a biopolymer track called microtubule. The kinesin-microtubule system has been studied in vitro. Two main configurations exist. In the first one, the gliding mode, microtubules are propelled by kinesin proteins bound to a substrate. In the second one, the kinesin molecules ``walk'' on the microtubule. Kinesin can be engineered in order to allow binding of specific cargo. In this study, we are using biotinated kinesin which allows strong non-covalent binding with streptavidin, which can cover any nano object. Using fluorescence microscopy, transport of quantum dots has been studied. Velocities have been analyzed and the results are in good agreement with data from the literature. New approaches using multiwall carbon nanotube tracks, aligned by dielectrophoresis, have also been investigated.
    03/2013;
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    ABSTRACT: Kinesin, an enzyme molecule found in eukaryotic cells, walks on specific paths, namely microtubules. These microtubules, self-assembled in-vitro, cooperate with kinesin molecules by playing the role of either a track for the molecular motors or a lengthy cargo lorry driven by the motor molecules. One of major challenges in utilization of the latter case, which is particularly advantageous for practical applications because of the longer cruising range and the higher carrying capacity of the bio-transporter, is herding the gliding microtubules. A general approach to achieve this goal is aligning motor molecules along a track. In previous attempts such tracks were physically and/or chemically patterned on a glass surface. We use a kinesin-coated glass wire to demonstrate kinesin-powered gliding movement of microtubules confined by the wire-like structure. This new approach distinguishes itself in that the glass wire track is an independent entity, being separable from a two-dimensional surface in principle. We will also discuss quantitative analysis of the guided motility and potential applications.
    03/2013;
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    ABSTRACT: The synthesis and in-situ organic surface modification of spinel cobalt aluminate nanoparticles were carried out under subcritical reducing hydrothermal conditions (250 °C, 30 MPa). Single nanoparticles of cobalt aluminate were obtained using a continuous flow-type reactor; in contrast, Co1−xAlx layered double hydroxide (Co-Al-LDHs) became the main product when a batch-type reactor was used. The addition of a surface modifier, hexanoic acid, to the flow-type reaction system changed the hydrophilic surface of the nanoparticles to a hydrophobic surface. Cobalt aluminate nanoparticles modified with hexanoic acid were well dispersed in hexane. The in-situ surface modification during the synthesis of the nanoparticles reduced the particle size from 15 nm to 10 nm.
    Chemical Engineering Science 01/2013; 85:50–54. · 2.39 Impact Factor
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    ABSTRACT: At the nano-scale many proteins act as biological actuators for rotation or translation. Among these proteins, the building blocks of self-assembled, highly efficient natural motors, kinesin is considered a promising tool in the development of synthetic nanorobots. Conversion of chemical energy into mechanical work, harnessed by the hydrolysis of adenosine triphosphate, propels kinesin along a cytoplasmic system of fibers, known as a microtubule. Even though recent efforts were made to engineer tailor-made artificial nanotransport systems using kinesin, no systematic study investigated how these systems can be organized from the bottom up using the surface plasmon resonance technique. Here, we show that it is possible to quantitatively evaluate how each component of such nanoscopic machines is sequentially assembled by monitoring the individual association of its components, focusing specifically on the kinesin association to microtubules as well as the cargo-kinesin association. Furthermore, the kinetic parameters reported here for the microtubules and recombinant biotinylated kinesin binding process properties are of utmost importance due to the current widespread use of biotinylated kinesin in the construction of synthetic nano-machines.
    Journal of Applied Physics 12/2012; 112(12). · 2.21 Impact Factor
  • Journal of chemical engineering of Japan 11/2012; 45(11):917-923. · 0.62 Impact Factor
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    ABSTRACT: Hafnium oxide nanoparticles were synthesized via a short-duration (10 min) hydrothermal reaction. The reaction was found to produce three differently shaped nanoparticles: flower-like nanostructures (20 nm diameter), polycrystalline nanoagglomerates (25 nm diameter), and water-dispersible single nanoparticles (4 nm diameter). The mechanisms by which these different shapes form were then investigated by examining the effects of precursor alkalinity and the presence of an organic capping agent. The synthesized water-dispersible nanoparticles showed a very high affinity for water-soluble polymers, thus demonstrating their potential for fabrication of transparent nanocomposite films.
    Crystal Growth & Design 11/2012; 12(11):5219-5226. · 4.69 Impact Factor
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    ABSTRACT: The mechanical stabilities of K4 carbon and K4-like NaC2 have been studied by performing first-principle calculations. Total energies as functions of isotropic deformations and volume-conserving tetragonal and trigonal deformations have been calculated. For K4 carbon, the total energy shows a minimum for isotropic and trigonal deformations, but exhibits maxima for tetragonal deformation. In contrast, the total energy of K4-like NaC2 shows a minimum under all three deformations. These results indicate that K4 carbon is not a metastable phase, but that K4-like NaC2 is a metastable phase. In addition, the heat of formation of K4-like NaC2 is discussed.
    Journal of Physics and Chemistry of Solids 11/2012; 73(11):1264–1267. · 1.53 Impact Factor
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    ABSTRACT: Novel one-dimensional nanostructures of yttrium aluminum garnet were synthesized under supercritical hydrothermal conditions in the presence of organic amine molecules. In addition, the effect of different reaction parameters such as the presence of organic amine molecules, pH of the precursor solution, and the state of water (sub- or supercritical conditions) on the morphology of the final product was investigated. In this paper, considering the simultaneous effects of these different parameters, a new electrostatic model is proposed to explain the formation mechanism of the obtained nanostructures.
    CrystEngComm 09/2012; 14(18):6085-6092. · 3.88 Impact Factor
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    ABSTRACT: In our study, water dispersible magnetite (Fe3O4) nanoparticles were continuously synthesized in water under high temperature and pressure in the presence of 3,4-dihydroxyhydrocinnamic acid (DHCA) by using a tubular flow reactor. The prepared Fe3O4 nanoparticles were well dispersed in water because the surfaces of the nanoparticles were fully covered by DHCA molecules and the –COOH groups in the DHCA molecules were exposed to the surrounding water. Cytokines such as IL-12 and TNF-α were not produced from the dendritic cells of mice by co-incubation with our synthesized Fe3O4. This indicates that the synthesized Fe3O4 had no immune stimulating property for the dendritic cells of the mouse. Therefore, our synthesized Fe3O4 nanoparticles are suitable for biological applications such as magnetic resonance imaging contrast agents and carriers for drug and gene delivery, and in areas such as hyperthermia therapy for cancer, biosensors, and tissue engineering.
    Journal of Materials Chemistry 05/2012; 22(18):9041-9045. · 5.97 Impact Factor

Publication Stats

2k Citations
480.55 Total Impact Points

Institutions

  • 1992–2013
    • Tohoku University
      • • Institute of Multidisciplinary Research for Advanced Materials (IMRAM)
      • • Graduate School of Engineering
      • • Department of Chemical Engineering
      • • Research Center of Supercritical Fluid Technology
      Japan
  • 2007–2008
    • University of Mysore
      Mahisūr, Karnātaka, India
    • University of Tehran
      • School of Chemical Engineering
      Teheran, Tehrān, Iran
    • Kyushu University
      • Department of Materials Science and Engineering
      Fukuoka-shi, Fukuoka-ken, Japan
  • 2006
    • National Institute of Advanced Industrial Science and Technology
      • Research Center for Compact Chemical System
      Sendai, Kagoshima-ken, Japan
  • 2003
    • Sendai University
      Sendai, Kagoshima, Japan
    • Kumamoto University
      Kumamoto, Kumamoto Prefecture, Japan