Masahiko Ishii

Toyota Central R & D Labs., Inc., Nagoya, Aichi, Japan

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Publications (26)114.98 Total impact

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    ABSTRACT: Ein poröses Gel mit winkelunabhängiger Strukturfarbe wird leicht durch einen Selbstorganisationsansatz erhalten. Beim Quellen wechselt das Gel reversibel seine Farbe auf Veränderungen von Lösungsmittel und Temperatur hin, weil die Wellenlängendispersionen der Brechungsindizes von Gel und in den Poren eingeschlossenem Lösungsmittel beeinflusst werden.
    No preview · Article · Apr 2011 · Angewandte Chemie International Edition

  • No preview · Article · Feb 2011 · Advanced Materials
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    ABSTRACT: The potential of a self-assembled phase-separated macroporous polymer film filled with an appropriate solvent for application in a functional multicolor polymer-dispersed liquid crystal (PDLC) display is explored. The findings demonstrate that a phase-separated porous MMAA-BIS polymer network filled with mixed LCs of 5CB and 5PCH can exhibit changes in structural color covering the whole visible region and an opaque milky color upon temperature variation. This system may be available for energy-saving multicolor displays.
    No preview · Article · Feb 2011 · Advanced Materials
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    ABSTRACT: 3-D colloidal amorphous arrays prepared from two different submicron-sized silica particles, exhibit a specific structural color that remains unchanged during the alternation of viewing angle (see figure). The refractive index in amorphous photonic material changes identically in all directions. This isotropic feature of the dielectric distribution leads to wavelength-selective light scattering.
    Full-text · Article · Feb 2010 · ChemPhysChem
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    ABSTRACT: We have demonstrated for the first time that condensed gel particle suspensions in amorphous-like states display structural color with low angle dependence. This finding is in contrast to the common understanding that a periodic dielectric structure is fundamental to photonic band gap (PBG) production, and it validates the theory that a "tight bonding model" that is applicable to semiconductor systems can also be applied to photonic systems. More practically, this structural colored suspension represents a promising new material for the manufacture of reflective full-color displays with a wide viewing angle and nonfading color materials. This liquid system shows promise as a display material because electronic equipment used for display systems can easily be filled with the liquid in the same way that liquid crystals are currently used.
    No preview · Article · May 2009 · ACS Applied Materials & Interfaces
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    ABSTRACT: Like other conventional smart materials, structural color showing smart materials inherit physical and chemical characteristics imposed by the templates. Smart Material such as structural colored gel made of photonic crystal (PC) as template, exhibits angle dependent structural color because the color arises from the Bragg optical diffraction of light from crystal planes. But angle independent or low angle dependent structural color is required for devising of display with a wide viewing angle. To meet this purpose we prepared photonic glass (PG) from silica colloidal spheres. This PG is able to exhibit structural color, which is stable against the change of the angle of view and the angle of illumination. The transmittance spectrum evidences the angle independence of the structural color of PG. The Fast Fourier Transformation and the autocorrelation function prove that we prepared an amorphous material. The existence of short range order helps PG to exhibit angle independent structural color.
    Full-text · Article · Feb 2009
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    ABSTRACT: It is important to check distortion in an opaline photonic crystal, since it may affect the photonic band structure and optical properties of the crystal. In this paper, we demonstrate that the existence of distortion can be checked by measuring both angle-resolved reflection spectra produced by two-dimensional (2D) diffraction and mirror reflection spectra. The lattice constant (a2D) determined by 2D diffraction is derived from the periodicity in the surface plane of the opaline crystal. In contrast, the lattice constant (am) determined from the mirror reflection spectra results from the periodicity in the direction perpendicular to the surface. Therefore, the existence of distortion can be checked by comparing these two lattice constants (a2D and am). The measurements revealed that the structure of an opaline photonic crystal composed of polystyrene (PS) spheres had the structure shrunken approximately 4% in the direction perpendicular to the surface. The origin of this distortion is discussed in terms of shrinkage of the PS spheres.
    No preview · Article · Aug 2007 · Journal of Optics A Pure and Applied Optics
  • Masahiko Ishii · Masashi Harada · Hiroshi Nakamura
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    ABSTRACT: Growth processes of colloidal crystalline arrays in a fluidic glass cell were observed in situ by confocal laser scanning microscopy. The results showed that the growth direction varied with the growth rate. At an extremely low growth rate, the array grew toward the 〈112〉 direction of the face-centered-cubic lattice. At a moderate growth rate, it grew toward the 〈110〉 direction. However, an extremely high growth rate induced random arrays of the spheres. Moreover, we were able to visualize the generation and/or annihilation processes of several kinds of defects. The variation of the growth direction with the growth rate is discussed in terms of the difference in water-flow resistance in the crystalline arrays.
    No preview · Article · Jun 2007 · Soft Matter
  • Masashi Harada · Masahiko Ishii · Hiroshi Nakamura
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    ABSTRACT: Colloidal crystals melt by applying focused light of optical tweezers and recrystallize after removing it. The disturbed zone by the light grows radially from the focus point and the ordering starts from the interface with the crystal. Although the larger disturbed zone is observed for the higher power optical tweezers, a master curve is extracted by normalization of the disturbed zone. The temporal changes of the normalized disturbed zone are well described with exponential functions, indicating that the melting and recrystallization process is governed by a simple relaxation mechanism.
    No preview · Article · May 2007 · Colloids and surfaces B: Biointerfaces
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    ABSTRACT: We acquired angle- and polarization-resolved reflection spectra from a colloidal crystal made of polystyrene spheres along the two perpendicular directions corresponding to the LU and LW directions in the first Brillouin zone of an fcc lattice. Dispersion relations between the reflection peak positions and the wave vectors of the incident light were obtained from the measured spectra and compared with calculated photonic band structures. For the first stop band region in the spectra, the behavior of the reflection peak due to Bragg diffraction agreed with the calculated band structure and revealed some differences induced by the polarization and crystalline orientations. The spectral features observed in the higher energy regions also revealed these differences. In addition, dispersion relationships between the peak positions and the wave vectors were obtained from the results of fitting each spectrum with several Gaussian curves, compared with the calculated photonic band structures. The relationships obtained for the LU direction almost matched the calculated band structure, while the relationships obtained for the LW direction revealed the features of the mixed band structure calculated for the two perpendicular directions. These results indicate that angle- and polarization-resolved reflection spectroscopy has the potential to experimentally analyze the photonic band structures of actual photonic crystals.
    No preview · Article · May 2007 · Colloids and surfaces B: Biointerfaces
  • Hiroshi Nakamura · Masahiko Ishii
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    ABSTRACT: The effects of medium composition on the optical properties and microstructures of non-close-packed silica colloidal crystalline arrays have been demonstrated. Water–alcohol mixtures were used as dispersion media for these arrays. Optical properties and microstructures were examined using angle-resolved reflection spectra measurements. The Bragg diffraction peaks of the colloidal crystalline arrays shifted with changing of concentration or hydrocarbon number of alcohol. With an increase in concentration or hydrocarbon number of alcohol, the effective refractive index of the dispersion increased and the interplanar spacing of the colloidal crystalline array decreased. The increase in effective refractive index was caused by an increase in the refractive index of the mixed medium with the change in solvent. The decrease in interplanar spacing of the array was caused by decreased electrostatic repulsions between the silica spheres with decreasing dielectric constant. The current work suggests new possibilities for the control of optical properties and microstructures of colloidal crystalline arrays.
    No preview · Article · Mar 2007 · Colloid and Polymer Science
  • Hiroshi Nakamura · Masahiko Ishii
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    ABSTRACT: Non-close-packed silica colloidal crystalline array was immobilized by polymer, and effects of stretching on the change of the optical properties and microstructure of the colloidal crystalline arrays have been demonstrated. The immobilization was a two-step polymerization process: the first step was with hydrophilic polyethylene glycol acrylate (PEGA) polymer gel, and the second step was with 2-hydroxyethyl acrylate polymer matrix. The structure of the three-dimensional array was maintained during the immobilizing process with lock in periodic order. The peak wavelength of Bragg diffraction of the polymer-immobilized colloidal crystalline array shifted to shorter wavelength with stretching. The peak shift was caused by the compression of the polymer proportional to the stretching ratio, and the compression was homogeneous throughout the polymer-immobilized colloidal crystalline arrays. These results show that by using polymer-immobilized non-close-packed colloidal crystalline array, mechanically tunable photonic crystals can be realized, and they open the possibility of tuning the microstructure of colloidal crystalline array for photonic crystal.
    No preview · Article · Feb 2007 · Colloid and Polymer Science
  • Hiroshi Nakamura · Masahiko Ishii
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    ABSTRACT: We have evaluated the optical properties of close-packed and non close-packed colloidal crystalline arrays made of hollow polystyrene spheres. Close-packed colloidal crystalline arrays were fabricated by simple evaporation of dispersions, whereas nonclose-packed colloidal crystalline arrays were fabricated by exploiting electrostatic interactions between the spheres in aqueous dispersion. Optical properties of the arrays were estimated from angle-resolved reflection spectra. The Bragg diffraction peak of the colloidal crystalline array made of hollow spheres was of shorter wavelength than in the case of solid spheres, not only for the close-packed array but also for the nonclose-packed array. These shifts were caused by a decrease in the effective refractive index neff with decreasing particle refractive index. We have found that this relationship could be explained by the simple equation neff = nparticleϕ+ nsolvent (1 − ϕ), where ϕ is the volume fraction of the particles, for both close-packed and non close-packed arrays. The current work suggests new possibilities for the creation of advanced colloidal crystals. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2364–2368, 2007
    No preview · Article · Feb 2007 · Journal of Applied Polymer Science
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    ABSTRACT: Opaline-type colloidal crystals composed of monodispersed microspheres have recently attracted great attention because of their application in photonic crystals. Polystyrene (PS) and silica spherical particles as are often used as materials for colloidal crystals. In this paper, the growth process and structure of the colloidal crystal composed of PS microspheres fabricated in a fluidic cell were investigated in comparison with those of the colloidal crystal composed of silica microspheres. During the growth process of both colloidal crystals, three distinct states were observed, in each of which the crystals exhibited different optical properties. Angle-resolved reflection spectroscopy revealed that PS microspheres undergo a shrinkage of ca. 3% in diameter at the drying process. The origin of the cracks observed on the PS colloidal crystal surface was discussed on the basis of the shrinkage.
    No preview · Article · Jan 2007 · KOBUNSHI RONBUNSHU
  • Hiroshi Nakamura · Takuya Mitsuoka · Masahiko Ishii
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    ABSTRACT: We have investigated to immobilize non close-packed silica colloidal crystalline arrays in aqueous dispersion with hydrophilic polyethylene glycol acrylate polymer and to examine microstructures of the immobilized colloidal crystalline array by using the angle-resolved reflection spectroscopy and scanning probe spectroscopy (SPM). Above nine of ethylene glycol chain length and below 10 wt % of monomer concentration in the dispersion, the structure of the three-dimensional array in the aqueous dispersion is kept with immobilizing process. Angle-resolved reflection spectra indicate refractive index increase, and interplaner spacing decreases with the increase of the particle volume fraction. The SPM phase images proved the crystal structure of the immobilized colloidal crystalline array of face-centered cubic (fcc) structure. The interplaner spacings of the crystalline structure derived from angle-resolved reflection spectra agree with those derived from SPM topographic images. We have demonstrated the microstructure of the polymer-immobilized colloidal crystalline array directly and open the possibility of tuning the microstructure of colloidal crystalline array for photonic crystal. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2308–2314, 2006
    No preview · Article · Nov 2006 · Journal of Applied Polymer Science
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    ABSTRACT: Inverse opal having mesoporous silica walls has been synthesized using close-packed polystyrene beads and octadecyltrimethylammonium chloride as a templates, and tetramethoxysilane as a silica precursor. The synthesized bimodal porous silica was characterized by XRD, N2 sorption, SEM and TEM. Hollow silica with inverted opaline structure had a macroporous diameter of 390 nm and a wall thickness of approximately 30 nm, and the mesoporous silica walls had a specific surface area of 367 m2/g, a mesopore diameter of 2.9 nm and a wall thickness of 1.8 nm. The refractive index (n) of this material was found be 1.05, which is lower than that of silica (n = 1.44) and also close to that of the air.
    No preview · Article · Nov 2006 · Microporous and Mesoporous Materials
  • Masashi Harada · Masahiko Ishii · Hiroshi Nakamura
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    ABSTRACT: The reflection from colloidal crystals of core-shell particles is evaluated by the calculation of photonic band structures, and is compared with the prediction of the Bragg condition. Although the results of the calculation of the photonic band structures are consistent with those of the Bragg condition, generally, the photonic band structures predict another reflection which has no origin in the Bragg condition, when the shell of the particle is sufficiently thin and the difference in refractive index between the core and the shell is relatively large. Moreover, no reflection is expected in the case of moderate shell thickness and moderate refractive index difference.
    No preview · Article · Oct 2006 · Japanese Journal of Applied Physics
  • Masashi Harada · Masahiko Ishii · Hiroshi Nakamura
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    ABSTRACT: We present the photonic band schemes of colloidal crystals with rhombohedral structures that are compressed along the [111] direction of a close-packed face-centered structure while maintaining the shapes of the colloidal particles. The compressed colloidal crystals transform from an A10 structure to an Ai structure through a simple cubic structure. The photonic band schemes reveal that, as the colloidal crystals are compressed, the stop-band frequencies increase for A10 structures and decrease for Ai structures upon becoming simple cubic structures. This transition can be explained by the change of the lattice plane responsible for Bragg diffraction.
    No preview · Article · Jul 2006 · Japanese Journal of Applied Physics
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    ABSTRACT: Titania coated monodisperse silica spheres have been synthesized and fabricated as a close-packed colloidal crystalline array. We have demonstrated that the coated colloidal sphere can be used to control the peak position of the optical stop band through variation of the coating thickness. The titania coated silica spheres were prepared by the layer-by-layer assembly coating process, which reciprocally laminates the cationic polyelectrolyte and the anionic titania nanosheets on a monodisperse silica spheres, and were sintered to change the titania nanosheets to anatase. The Bragg diffraction peak of the colloidal crystalline array shifted to the long wavelength region with an increase of thickness of the titania layer. Angle-resolved reflection spectra measurements clarified that the red shift was caused by increasing of the refractive index with increase of the thickness of the layer. The current work suggests new possibilities for the creation of advanced colloidal crystalline arrays with tunable optical properties from tailored colloidal spheres.
    No preview · Article · Feb 2006 · Langmuir
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    ABSTRACT: Colloidal crystalline arrays are three dimensionally periodic lattices of self-assembled monodisperse colloidal spheres. These periodic structures have been actively explored as functional components in fabricating new types of diffractive devices such as optical filters and chemical sensors, mechanical sensors, and photonic bandgap structures. We have demonstrated the synthesis of silica or polystyrene spheres uniformly coated with titania nanosheets and the fabrication of these spheres into close-packed colloidal crystalline arrays. We have also reported on the optical properties and microstructures of the colloidal crystalline array estimated by angle-resolved reflection spectra measurements. The titania nanosheets were synthesized by delamination of layered titanate crystallites. The titania nanosheets coated spheres were prepared by the LBL (Layer-By-Layer) assembly coating process, which consisted of alternately laminating cationic polyelectrolyte and anionic titania nanosheets on monodisperse silica or polystyrene spheres. The close-packed colloidal crystalline array was fabricated in the glass cell by drying process of the aqueous dispersion of the spheres. The Bragg diffraction peak of the colloidal crystalline array shifted to longer wavelengths with increasing thickness of titania nanosheets layers. Angle-resolved reflection spectra measurements showed that this red shift was caused by increasing the mean effective refractive index neff of this crystalline lattice without changing interplanar spacing d111 with increasing thickness of titania nanosheets layers. Since a wide range of coated colloids of different size, composition, and optical properties can be prepared via the LBL coating, the current work suggests new possibilities for the creation of advanced colloidal crystalline arrays with tunable optical properties.
    No preview · Article · Jan 2006 · Proceedings of SPIE - The International Society for Optical Engineering