Khanin Nueangnoraj

Production of Colored Pigments with Amorphous Arrays of Black and White Colloidal Particles

There are many technical and industrial applications for colored pigments with nonfading properties. The development of a low-cost, high-volume production method for nonfading pigments with low toxicity and minimal environmental impact may promote their widespread use. To accomplish this goal, pigments need to be prepared using abundant and environmentally friendly compounds. Here, we report on the variously colored aggregates formed by spraying fine, submicrometer-sized spherical silica particles. The microstructure of the aggregate is isotropic with a shortrange order on a length scale comparable to optical wavelengths, and exhibits an angle-independent structural color as a result of wavelength-specific constructive interference. Interestingly, the color saturation of these aggregates can be controlled by the incorporation of a small amount of conventional black particles, such as carbon black (CB). We demonstrate that a Japanese-style painting can be successfully drawn with this method. Silicon dioxide, which is a major component of silica particles, is chemically stable and used in scientific glassware suitable for chemical experiments. It is also a primary component of soil and found in abundant supply in nature. Furthermore, in vivo toxicity of silica particles that are greater than 300 nm in diameter has not been detected. Therefore, submicrometer-sized silica particles are one of the best candidates for fabricating environmentally friendly materials. Fine submicrometer-sized spherical silica particles usually appear white to the human eye when they are in powdered form. However, assemblies of these particles can appear colored because of wavelength-specific optical interference, 5, 7] despite the absence of light-absorbing pigments and dyes. Such color is generally referred to as structural color, because it is essentially caused by the microstructure through optical phenomena, such as interference, diffraction, and scattering. 9] Crystalline arrays of fine submicrometersized spherical silica particles (colloidal crystals) are well known examples of assembled particles that have structural colors as a result of a very high reflectance at a certain wavelength of light. However, the structural colors produced by colloidal crystals show distinct variations, which depend on viewing and light illumination angles. Such iridescence makes the use of colloidal crystals as pigments difficult, because typical pigments generally require a constant color at different viewing angles. The iridescences of the colloidal crystals originate from Bragg reflection, which is the reflection mechanism that occurs as a result of the long-range order in the particle arrangement. Thus, if the arrangement is changed from the crystalline structure to the amorphous state, which has only a short-range order, iridescence is expected to be suppressed. In fact, amorphous aggregates of colloidal particles have been reported to exhibit angle-independent structural colors. 4, 5,12] However, amorphous colloidal arrays are difficult to fabricate because submicrometer-sized particles have a strong tendency to crystallize. Previously, amorphous colloidal arrays have been prepared by mixing two different kinds of submicrometer-sized silica particles. 4, 5, 13] These mixtures exhibit structural colors, but the colors are very pale. 4,5] Therefore, such amorphous colloidal arrays are unsuitable for use as brightly colored pigments. A simple synthetic method for the preparation of assemblies of submicrometer-sized particles with angle-independent brilliant structural colors for use as pigments has not yet been reported. Herein, we report a simple and reproducible synthetic procedure for the preparation of pigments that exhibit angleindependent, bright structural colors from amorphous colloidal arrays by spraying fine submicrometer-sized spherical silica particles of uniform size. We added a small amount of black particles to the colloidal amorphous array to enhance the saturation of the structural color by reducing incoherentlight scattering across the entire visible spectrum. Variously [*] Prof. Y. Takeoka, Prof. A. Takano, M. Teshima, Y. Ohtsuka, Prof. T. Seki Graduate School of Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya, 464-8603 (Japan) E-mail: ytakeoka@apchem.nagoya-u.ac.jp

Structural Coloration of a Colloidal Amorphous Array is Intensified by Carbon Nanolayers

In this study, we introduce the possibility of applying a colloidal amorphous array composed of fine silica particles as a structural-color material to invisible information technology. The appearance of a thick filmlike colloidal amorphous array formed from fine silica particles is considerably influenced by incoherent light scattering across the entire visible region. Therefore, regardless of the diameter of the fine silica particles, the thick colloidal amorphous array exhibits a white color to the naked eye. When carbon is uniformly deposited in the colloidal amorphous array by a pressure-pulsed chemical vapor deposition method, incoherent light scattering in the colloidal amorphous array is suppressed. As a result, coherent light scattering due to the short-range order in the colloidal amorphous array becomes conspicuous and the array exhibits a vivid structural color. As structures, such as letters and pictures, can be drawn using this technology, the colloidal amorphous array as a structural-colored material may also be applicable for invisible information technology.

Zeolite-templated carbon as electrodes for electrochemical energy storage

This work presents the use of zeolite-templated carbon (ZTC), which is a microporous carbon obtained from the chemical vapor deposition of carbon source gas over zeolite Y template, as an electrode for the electrochemical capacitors (ECs). Two different structures of ZTC, fullerene-like and buckybowl-like, were examined to realize a high-performance electrode for ECs.