Yusuke Yamauchi

A High‐Speed Passive‐Matrix Electrochromic Display Using a Mesoporous TiO2 Electrode with Vertical Porosity

Recently, the application of electronic paper (E-paper) has attracted considerable attention. Many types of reflective displays, such as reflective liquid crystal displays and electrophoretic displays, have been introduced and applied to E-paper. Among them, electrochromic materials, which change in color intensity when an appropriate potential is applied, are the subject of an increasing number of reports. Recently, polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT) or catenanes were reported to show electrochromic behavior. The slow response time for coloring has been a serious problem with these kinds of polymers. As probable electrochromic materials, viologens have commonly been utilized for electrochromic displays (ECDs). Many studies have focused on viologen-modified microspheres or nanostructures to increase the switching speed. Viologens are basically blue in color, and it is thus difficult to realize a full-color display. Furthermore, these kinds of displays have a common drawback: poor background whiteness. To date, electronic displays have not been able to meet the requirements necessary for extensive practical applications. Currently, full-color reflective displays that demonstrate a fast response time are in much demand. Usually, display devices are driven by either active-matrix drive mode or passivematrix drive mode. Active-matrix drive mode is very fast, but it needs expensive thin-film transistors (TFT) for all the pixels of the display, which leads to a high price. Passive-matrix drive mode does not need such expensive electric elements, and it has a simple, low-cost structure. However, when ECD devices are driven by passive-matrix mode at high scanning speed, the drift of electrochromic materials around the electrode leads to poor resolution. That is, the display images are blurry. Herein, we aim to realize high scanning speed and high display quality. We focused on leuco dyes, which are well known as recording materials in thermal imaging systems, because the leuco dyes show a wide variety of colors and are commercially available. We demonstrated a high-speed and high-resolution electrochromic passive-matrix display using a leuco dye with a mesoporous TiO2 electrode with vertical pores (Figure 1). The vertical pores of the electrode can support effective diffusion of leuco dyes perpendicular to the electrode and can prevent the diffusion of the dye around the electrode. Since the colorless state of this kind of display is transparent, it exhibits better background whiteness, which improves readability and reduces eyestrain. Furthermore, the application of leuco dyes to ECD devices has high potential to realize a full-color reflective display with low production costs. These features are very desirable for future E-paper applications. Our device, which consists of two electrodes (working electrode and counter electrode) and electrolyte (Figure 1), was driven by the passive-matrix driving method (an addressing scheme used in earlier liquid crystal displays). Each electrode has striped indium–tin-oxide (ITO) layers 420 mm wide on a glass substrate (Figure 1b and Figure S1 in the Supporting Information). The mesoporous TiO2 film was grown only on the observation side of the working electrode. By improving the previous method, continuous TiO2 films with highly ordered mesostructure and vertical pores were uniformly prepared on the working electrodes by spin coating with a precursor solution. The film thicknesses were changed by using different spinning speeds. Thicknesses of approximately 300, 200, and 100 nm were realized by speeds of 2000, 4000, and 6000 rpm, respectively. Cross-sectional and topsurface SEM images showed that mesopores were oriented vertically with respect to the substrate (Figure S1c in the Supporting Information). The mesochannel walls are composed of periodically arranged cages with connecting necks between the neighboring cages (see the Supporting Information, in particular Figure S2, for details). The two electrodes sandwiched the electrolyte so that the striped ITO layers were orthogonally crossed (Figure 1b and Figure S3 in the Supporting Information). The electrolytic solution consisted of black leuco dye (2-(3’-trifluoromethylphenylamino)-6’[*] W. Weng, T. Higuchi, M. Suzuki, T. Fukuoka, Dr. T. Shimomura, Dr. M. Ono Funai Electric Advanced Applied Technology Research Institute Inc. 2-1-6 Sengen, Tsukuba, Ibaraki 305-0047 (Japan) E-mail: weng.w@funai-atri.co.jp

Controlled Aqueous Solution Synthesis of Platinum–Palladium Alloy Nanodendrites with Various Compositions Using Amphiphilic Triblock Copolymers

In a recent study, we demonstrated that Pluronic F127 triblock copolymer plays a critical role in the formation of dendritic Pt nanostructures (L. Wang, Y. Yamauchi, J. Am. Chem. Soc. 2009, 131, 9152-9153). Herein, we expand this concept to produce novel dendritic Pt-Pd alloy nanoparticles. In this paper, a very simple, one-step and efficient route is proposed to directly produce dendritic Pt-Pd alloy nanoparticles with high surface area in high yield, which is carried out simply by stirring an aqueous solution that contains K(2)PtCl(4) and Na(2)PdCl(4) binary precursors in the presence of Pluronic F127 block copolymer and ascorbic acid at room temperature within 30u2005min without the need for any template, seed-mediated growth, or additive. By simply changing the compositional ratios of the Pt and Pd sources in the precursor solutions, Pt-Pd nanodendrites with various compositions can be easily produced. Because of its unique simplicity, the proposed approach can be considered as a powerful strategy for producing Pt-Pd alloy nanoparticles with unique nanoarchitectures for commercial devices.

Mesoporous silica as smart inorganic filler: preparation of robust silicone rubber with low thermal expansion property

Here we demonstrate the importance of mesoporous silica as a smart inorganic filler. Silicone rubber with low thermal expansion is realized by doping mesoporous silica particles. For the preparation of mesoporous silica/silicone composites, an unpolymerized silicone component is diluted by a volatile organic solvent and then is penetrated into the mesopores by a capillary force. After penetration, the organic solvent is evaporated completely. Based on theoretical calculations, the estimated degree of mesopore filling is more than 90%. Mesoporous silica/silicone composites show much lower Coefficient of Linear Thermal Expansion (CTE) and higher hardness values than do silicone composites with nonporous silica particles.

Preparation of aqueous colloidal mesostructured and mesoporous silica nanoparticles with controlled particle size in a very wide range from 20 nm to 700 nm

Particle size control of colloidal mesoporous silica nanoparticles (CMPS) in a very wide range is quite significant for the design of CMPS toward various applications, such as catalysis and drug delivery. Various types of CMPS and their precursors (colloidal mesostructured silica nanoparticles (CMSS)) with different particle sizes (ca. 20-700 nm) were newly prepared from tetraalkoxysilanes with different alkoxy groups (Si(OR)4, R = Me, Et, Pr, and Bu) in the presence of alcohols (ROH, R = Me, Et, Pr, and Bu) as additives. CMSS with larger particle size were obtained by using tetrabutoxysilane (TBOS) and by increasing the amount of BuOH, which is explained by both the difference in the hydrolysis rates of tetraalkoxysilanes themselves and the effect of added alcohols on the hydrolysis rates of tetraalkoxysilanes. Larger amounts of alcohols with longer alkyl chains decrease the hydrolysis rates of tetraalkoxysilanes and the subsequent formation rates of silica species. Thus, the preferential particle growth of CMSS to nucleation occurs, and larger CMSS are formed. Highly dispersed CMPS were prepared by the removal of surfactants of CMSS by dialysis which can lead to the preparation of CMPS without aggregation. Therefore, the particle size control through the tuning of the hydrolysis rate of tetraalkoxysilanes can be conducted by a one-pot and easy approach. Even larger CMPS (ca. 700 nm in size) show relatively high dispersibility. This dispersibility will surely contribute to the design of materials both retaining nanoscale characteristics and avoiding various nanorisks.

General synthesis of fibrous mesoporous metal oxides in polycarbonate membrane

Mesoporous metal oxide fibers such as silica, alumina, titania, zirconia, niobia, and tantala were fabricated through the penetration of surfactant-containing precursor solutions into the cylindrical confined spaces of polycarbonate (PC) membrane, followed by calcination to remove both the surfactants and the PC membrane completely. The SEM images showed that the average diameters of the mesoporous fibers were ca. 200 nm, being related to that of the confined spaces of the original PC membrane. The cylindrical spaces of the PC membrane are more useful as a hard template for compositional variation than those of porous anodic alumina membranes that have been used for the synthesis of ordered mesoporous silica fibers. The TEM images, the SAXS profiles, and the N2 adsorption-desorption isotherms supported the formation of mesoporous structures inside the fibers. Calcination at a temperature appropriate for each fiber directed to the crystallization of the non-silica-based frameworks with the retention of mesoporous structures. The wide-angle XRD patterns of the non-silica fibers revealed the crystallization to typical Al2O3 (γ-phase), TiO2 (anatase), ZrO2 (tetragonal), and Nb2O5 (pseudo-hexagonal) phases, which was also supported by the corresponding EDS mappings.

Highly Photoactive Porous Anatase Films Obtained by Deformation of 3D Mesostructures

A transparent film of three-dimensional (3D) hexagonal (P6(3)/mmc) mesostructured titania was fabricated according to a modified procedure using triblock copolymer Pluronic P123. The precursor solution was diluted with ethanol and spin-coated to afford a transparent film with a thickness of less than 100u2005nm. The mesostructure was maintained (deteriorated) at 400u2009°C, converted to regularly arranged anatase nanopillars with sufficient porosity at 550u2009°C, and deformed at 700u2009°C to nanocrystals with intercrystalline mesospaces. The mesostructural variation was related to the degree of shrinkage of the film owing to condensation and crystallization of the titania frameworks. An anatase nanocrystal film having sufficient porosity and high crystallinity was most active in the photodegradation of methylene blue. Such intercrystalline mesospaces can be controlled by regular deformation of 3D mesostructures through anatase nanopillar structures. In addition to adequate crystallinity of the titania frameworks, smooth diffusion of target organic molecules and/or degraded organic compounds was important for effective photodegradation.

Liquid crystalline inorganic nanosheets for facile synthesis of polymer hydrogels with anisotropies in structure, optical property, swelling/deswelling, and ion transport/fixation

Macroscopically anisotropic hydrogels were synthesized by hybridization of poly(N-isopropylacrylamide) with liquid crystalline inorganic nanosheets; their anisotropies in the structure and properties are demonstrated.

Oriented Growth of Small Mesochannels Utilizing a Porous Anodic Alumina Substrate: Preparation of Continuous Film with Standing Mesochannels

Standing mesochannels: An oriented growth on the mesoscale is demonstrated for the formation of standing mesochannels. The standing mesochannels in the continuous film grow epitaxially from the mesochannels oriented along the straight holes of porous anodic alumina substrate.

Mesoporous palladium–copper bimetallic electrodes for selective electrocatalytic reduction of aqueous CO2 to CO

Finding a highly efficient, selective and economic approach for electrochemical reduction of aqueous carbon dioxide is a great challenge in realizing an artificial system for a sustainable carbon cycle. Novel mesoporous palladium–copper bimetallic electrocatalysts with superior activity and high faradaic efficiencies (FEs) are reported for the first time. The mesoporous nanostructure provides a roughened surface which is abundant in active sites and promotes selective conversion of CO2 to CO. First-principles calculations exhibit that Pd atoms on the catalyst surface serve as reactive centers and highly selective CO formation is attributed to the geometric and electronic effects within the palladium–copper bimetallic alloys. The CO2 and COOH* intermediate adsorption ability and the CO desorption ability on Pd atoms are effectively enhanced in the presence of Cu. Our results provide wide ranging implications for further improving the design and preparation of CO2 reduction electrocatalysts.

Aerosol-assisted synthesis of mesoporous organosilica microspheres with controlled organic contents.

Abstract Periodic mesoporous organosilica (PMO) spherical particles with different organic contents were synthesized in one pot by reacting 1,2-bis(triethoxysilyl)ethane (BTSE) with tetraethylorthosilicate (TEOS) using a spray-drying technique. The scanning electron microscopy observation of spray-dried products clearly showed the formation of spherical particles. The 29Si magic angle spinning nuclear magnetic resonance data revealed that the organic contents due to ethane fragments embedded in the frameworks were controllable and consistent with the BTSE/TEOS molar ratios of precursor solutions. Transmission electron microscopy, small-angle x-ray scattering, and N2 adsorption data of PMO with controlled organic contents indicated that the ethane fragments were embedded in the frameworks with the formation of ordered mesostructures. PMO with a high organic content (BTSE/TEOS=0.50) only showed a hydrophobic property. According to the same procedure, benzene groups were also integrated to a similar degree in the frameworks by using 1,4-bis(triethoxysilyl)benzene.