In a previous paper, we reported that we have newly developed a robustness-enhancing halftone technology that can dramatically improve the significant graininess deterioration caused by the misregistration between reciprocating scans of an inkjet printer. As a result, the problem of graininess deterioration was solved, but on the other hand, the problem of density fluctuation due to the same cause remains, which causes a fatal problem of image quality such as density unevenness in the cockle generating area. Therefore, as a result of aiming to solve this problem, we found that the density fluctuation can be significantly reduced by setting the probability that both of a pair of short-distance pixels become dot-on as the square of the input gradation value. By applying it, we have also developed a new halftone technology that improves density robustness, and confirmed the effect with an actual printer.
Recently, we have synthesized oligo(3-methoxythiophene) doped with perchlorate ion and reported that the coating films exhibited gold tone luster. Although this oligomer is soluble in some polar organic solvents, the number of good solvents is limited. In this study, we identified the interaction between the oligomer and solvent as a dipole-dipole interaction, and found several good solvents. The coating films were prepared using the coating solutions of the good solvents, and their optical, color, and structural properties were investigated. The results revealed that the film with a higher luster and more intense yellowness was obtained when the solvent in which more π-dimers are formed was used for the coating solution.
We describe a nanostructure with a physical antibacterial function. Based on the hypothesis of previous studies that the antibacterial function is expressed by adsorption energy, we performed calculations by introducing adsorption energy and bacterial breakage conditions. The calculation results explained the difference in antibacterial effect of the nanostructured film on the bacterial species shown by previous studies. In addition, the antibacterial ability of the pillar structure according to the structural factors was illustrated almost comprehensively. The nanostructured film designed based on this hypothesis was realized by printing and showed antibacterial function. In addition, we measured the temporal changes of bacteria that came into contact with the nanostructured film by fluorescence microscopy, and confirmed the behavior that supported the hypothesis : the cell membrane was attracted to the nanostructured film side. Furthermore, we fabricated finer nanostructured membranes using the same principle for the effect on viruses, and confirmed the expression of the antiviral function.
Structural color is a color derived from the optical interaction between light and microstructure. In nature, natural melanin plays an important role in bright structural colors. For example, the structural color of a peacock feather is caused by the periodic arrangement of melanin granules inside the feather, and the black granules effectively absorb scattered light, resulting in a bright structural color. In recent years, polydopamine has been attracting attention as a melanin-mimicking material. This paper summarizes recent research on structural coloration using polydopamine-based artificial melanin particles. It also outlines possible applications including inks and sensor applications with bright structural colors achieved by artificial melanin materials.
There are many animals that show metal-like glittering colors like a jewel beetle. These colors are produced by microstrutures comparable with the wavelength of light, and thus, they are called structural colors. Various color-causing microstructures have been found such as multilayer and photonic crystals. The periodic microstructure causes the constructive optical interference at the wavelength of visible light, resulting a higher reflectance at specifice wavelenghs of light. However, rather than simple optical interference, animals have been found to utilize various factors to make the color brilliant and saturated. In this article, we describe the coloraition mechanisms for several types of microstructures with some biological examples. In addition, we mention the coloration mechanisms of a photonic ball, which is an artificially produced spherical aggregation of collidal particles.
Polythiophenes are multifunctional molecules and are considered as potential candidates for molecular electronics and imaging engineering. Among such polythiophenes, the author's group has found some derivatives that exhibit gold or bronze tones in their films formed by solution-casting or electropolymerization methods, and has conducted scientific and engineering investigations. In this review, the chemical synthesis of the thiophene derivatives and the physicochemical properties of their coating solution and cast films, as well as the electrochemical synthesis and the properties of the thiophene derivative films, are outlined. Through the series of the investigations described above, the mechanism is also discussed for the development of the gold-like luster. The thiophene derivatives prepared by chemical synthesis can be dissolved in some organic solvents and water, can be applied to various substrates such as glass plates and paper sheets, and show high stability in the air, making them good candidates for brilliant paints and inks.
A lot of novel elastic materials with tunable structural color by combine soft material and structural color have been reported in the past two decades. A typical example, colloidal crystals enable change structural color by deforming the particle spacing of the crystal lattice. We have proposed that elastic materials called photonic rubber to change their structural color due to tension (stretching), compression, and expansion due to external stress. One diffraction peak is observed in the reflection spectrum from a high-quality colloidal crystal oriented uniaxially. Since the diffraction peak shifts due to stress, application as a sensor is expected by utilizing the relationship between the shift amount and stress. We have investigated the basic characteristics of stretching, compression, and expansion of photonic rubber. Currently, we are conducting research for practical use. Regarding durability, there was no significant deterioration in the structural color change in the tensile test due to reciprocating motion exceeding 100 000 times. On the other hand, we are addressing more practical issues related to manufacturing costs, such as increasing the size of homogeneous colloidal crystals and increasing the rate of film formation.
From the perspective of biodiversity conservation, in the 21st century, environmentally friendly manufacturing is required to achieve the SDGs (sustainable development goals). Among the colored materials that make our lives colorful and rich, such as dyes and pigments, those that are harmful to human health and the environment need to be changed to safe materials. In nature, we are already using safe, low-fading structural colored materials that exhibit a variety of hues, without the use of toxic compounds and heavy metals. In this article, I would like to introduce bright angle-independent structural colored materials that use only safe and inexpensive white and black materials.
Perovskite quantum dots (PeQDs) have attracted attention as a light source for optoelectrical applications such as a light emitting device due to their optical properties e. g. high photoluminescence quantum yields (PLQY≈100%) and luminescence with narrow full width at half maximum (FWHM<25nm). These optical properties of PeQDs implied these were superior to other quantum dots such as cadmium serenade and indium (III) phosphide due to recent research. However, there were problems : the difficulty about the preparing conditions of PeQDs such as high temperature and the unestablished mass synthesis process for these industrializations. Herein, we review our various preparing methods of PeQDs with high optical properties for industrialization.
In recent years, structural colors using metasurface, which are two-dimensional metamaterials, have attracted much attentions. In particular, structural colors using metallic meta atoms are also called plasmonic colors, and color images with high resolution and a wide viewing angle comparable to the diffraction limit of 100 000 dpi have been realized. However, it has been difficult to achieve both high resolution and high saturation due to metal loss. This paper introduces the principle of dielectric metasurface structure color using single crystalline silicon and the current state of research. Since the dielectric metasurface is thinner than the wavelength and does not use metal, there is almost no loss, and a highly saturated structural color can be realized while maintaining high resolution and a wide viewing angle. Furthermore, by utilizing the oxidation of silicon at high temperature, it becomes possible to change the color later. This can be applied to secret images. The dielectric metasurface is expected to be applied to diffraction-limited resolution color printing with functionality.
To elucidate molecular structure of carthamin, the global traditional cosmetic red ingredient that has a green metallic luster, The conditions and all natural materials of the traditional extraction and purification method based on traditional method in Yamagata prefecture, The tablet of fermented safflower petals (Benimochi) was chemically analyzed with varied instruments in detail. Carthamin was purified excellent in dispersion stability with sufficient reproducibility. The traditional “Sasabeni” is carthamin-3' potassium salt. Green metallic luster was observed from the pigment film immobilized on the black base. A reflection maximum around 550nm was found on the measured spectrum, which corresponded to a green color. There was no angle dependence on the wavelength for the reflection maximum. The metallic luster is occured at the air/film or glass/film interface, and contained poor linearly polarized components. These results suggested that the green metallic luster is similar to the reflection of real metallic materials.