Papers - Oaki, Yuya

結晶を活用した高分子の形の制御

OAKI Yuya

高分子 66   221 - 222 2017.05

Accepted

Visualization and Quantitative Detection of Friction Force by Self-Organized Organic Layered Composites

H.Terada, H.Imai, Y.Oaki

Advanced Materials (Advanced Materials)  30 ( 27 )  2018

Research paper (scientific journal), Joint Work, Accepted,  ISSN  09359648

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Visualization and quantitative detection of external stimuli are significant challenges in materials science. Quantitative detection of friction force, a mechanical stress, is not easily achieved using conventional stimuli-responsive materials. Here, the quantitative detection of friction force is reported, such as the strength and accumulated ammount, from the visible color of organic layered composites consisting of polydiacetylene (PDA) and organic amines without an excitation light source. The composites of the layered diacetylene monomer crystal and interlayer organic amine are synthesized through self-organization from the precursor solution. After topochemical polymerization, the layered composites based on PDA show tunable temperature-responsive and mechanoresponsive color-change properties depending on the types of interlayer amines. The layered composites are homogeneously coated on a filter paper. The change in color of the paper is quantitatively used to visualize the strength and accumulated amount of the applied friction force. Furthermore, writing pressure is measured by friction force using the paper device.

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Emergence of temperature-dependent and reversible color-change properties by stabilization of layeredpolydiacetylene through intercalation

Y. Oaki, Y. Ishijima, H. Imai

Polymer Journal (Polymer Journal)  50 ( 4 ) 244 - 247 2018.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00323896

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The stimuli-responsive color-changing properties of functional polymers are applied to the development of sensing and imaging devices. Tuning the stimuli responsivity is required for a wide range of applications. Polydiacetylene (PDA) derivatives show color changes with the application of external stimuli, such as heat and mechanical stress. Our group has focused on the layered crystal structure of PDA and its intercalation chemistry. The original layered PDA shows an irreversible color transition from blue to red upon heating to the threshold temperature. Here, we found that alkyldiamine-intercalated PDA possessed different color-changing properties, such as a higher color transition temperature and a temperature-dependent and reversible color change, than the original PDA. As the alkyl-chain length increased, the color-changing behavior gradually converted from the irreversible color transition type to the reversible temperature-dependent one. Since the intercalated diamine had a stabilizing effect on the layered structure, the stimuli responsivity varied according to the type of diamine. The results suggest that the stimuli-responsive color-changing properties of layered PDA can be finely and systematically tuned by the intercalation of organic guests.

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Few-layered titanate nanosheets with large lateral size and surface functionalization: Potentials for controlled exfoliation of inorganic-organic layered composite

G. Nakada、H. Imai, Y. Oaki

Chemical Communications (Chemical Communications)  54 ( 3 ) 244 - 247 2018.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  13597345

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Herein, few-layered titanate nanosheets with a large lateral size and surface functionalization were synthesized via the exfoliation of precursor layered composites in an organic medium. The combination of layered compounds, intercalated guests, and dispersion media has the potential for the synthesis of nanosheets with controlled lateral sizes, thicknesses, and surface chemistry through exfoliation.

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Effects of intercalation rate on layered crystal structures and stimuli-responsive color-change properties of polydiacetylene

M. Takeuchi, H. Imai, Y. Oaki

Journal of Materials Chemistry C 5 ( 32 ) 8250 - 8255 2017.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2050-7526

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Tunable Mechano-responsive Color-Change Properties of Organic Layered Material by Intercalation

Y. Ishijima, H. Imai, Y. Oaki

Chem 3   509 - 521 2017.05

Research paper (scientific journal), Joint Work, Accepted

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Hierarchical bicontinuous structure of redox-active organic composites and their enhanced electrochemical properties

K. Sato, M. Arayasu, H. Masaki, H. Imai, Y. Oaki

Chemical Communications 53 ( 53 ) 7329 - 7332 2017.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1359-7345

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Real-Time Imaging of 2D and 3D Temperature Distribution: Coating of Metal-Ion-Intercalated Organic Layered Composites with Tunable Stimuli-Responsive Properties

M. Takeuchi, H. Imai, Y. Oaki

ACS Applied Materials and Interfaces 9 ( 19 ) 16546 - 16552 2017.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1944-8244

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Multistage Redox Reaction of Conductive-Polymer Nanostructures with Lithium Ion: Potentials for High-Performance Organic Anode

H.Numazawa, K.Sato, H.Imai, Y.Oaki

NPG Asia Materials  2018

Research paper (scientific journal), Joint Work, Accepted

Two exfoliation approaches for organic layered compounds: hydrophilic and hydrophobic polydiacetylene nanosheets

Y. Ishijima, M. Okaniwa, Y. Oaki, Hiroaki Imai

Chemical Science 8 ( 1 ) 647 - 653 2017.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2041-6520

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Phase separation through simultaneous polymerization and crystallization for composite materials

K. Sato, Y. Oaki, H. Imai

NPG Asia Materials 9   e377 2017.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1884-4049

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Coupled Exfoliation and Surface Functionalization of Titanate Monolayer for Bandgap Engineering

Y. Yamamoto, Y. Oaki, H. Imai

Advanced Materials Interface 4 ( 7 ) 1601014 2017.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2196-7350

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Conductive Polymer Nanosheets Generated from the Crystal Surface of Organic Oxidant

K. Sato, H. Masaki, M. Arayasu, Y. Oaki, H. Imai

ChemPlusChem 82 ( 2 ) 177 - 180 2017.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2192-6506

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Morphology Design of Crystalline and Polymer Materials from Nanoscopic to Macroscopic Scales

OAKI Yuya

Bulletin of the Chemical Society of Japan 90 ( 7 ) 776 - 788 2017.07

Single Work, Accepted,  ISSN  0009-2673

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Tunable photochemical properties of a covalently anchored and spatially confined organic polymer in a layered compound

H. Matsui, Y. Oaki, H. Imai

Nanoscale 8 ( 21 ) 11076 - 11083 2016

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2040-3364

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Surface-functionalized hydrophilic monolayer of titanate and its application to dopamine detection

H. Matsui, Y. Oaki, H. Imai

Chemical Communications 52   9466 - 9469 2016

Research paper (scientific journal), Joint Work, Accepted

Intercalation-Induced Tunable Stimuli-Responsive Color-Change Properties of Crystalline Organic Layered Compound

M. Okaniwa, Y. Oaki, H. Imai

Advanced Functional Materials 26 ( 20 ) 3463 - 3471 2016

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1616-301X

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Crystal-surface-induced simultaneous synthesis and hierarchical morphogenesis of conductive polymers

K. Kuwabara, Y. Oaki, H. Imai

Chemical Communications 51 ( 47 ) 9698 - 9701 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1359-7345

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Hydrophobic monolayered nanoflakes of tungsten oxide: Coupled exfoliation and fracture in a nonpolar organic medium

M. Honda, Y. Oaki, H. Imai

Chemical Communications 51 ( 49 ) 10046 - 10049 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1359-7345

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An Advanced Biomimetic Approach for Crystal Growth in Nonaqueous Media: Morphology and Orientation Control of Pentacosadiynoic Acid and the Applications

M. Okaniwa, Y. Oaki, S. Kaneko, K. Ishida, H. Maki, Hideyuki, H. Imai

Chemistry of Materials 27   2627 - 2632 2015

Research paper (scientific journal), Joint Work, Accepted

A hydrophobic adsorbent based on hierarchical porous polymers derived from morphologies of a biomineral

K. Sato, Y. Oaki, H. Imai

Chemical Communications 51 ( 37 ) 7919 - 7922 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1359-7345

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Hierarchical CaCO3 Chromatography: A Stationary Phase Based on Biominerals

K. Sato, D. Takahashi, Y. Oaki, K. Toshima, H. Imai

Chemistry- A European Journal 21   5034 - 5040 2015

Research paper (scientific journal), Accepted

Incorporation of organic crystals in the interspace of oriented nanocrystals: morphologies and properties

Y. Munekawa, Y. Oaki, H. Imai

Nanoscale 7   3466 - 3473 2015

Research paper (scientific journal), Joint Work, Accepted

Solvent-free Synthesis, Coating and Morphogenesis of Conductive Polymer Materials through Spontaneous Generation of Activated Monomers

Ryo Muramatsu, *Yuya Oaki, Kento Kuwabara, Kosei Hayashi, *Hiroaki Imai

Chem. Commun. 50 ( 80 ) 11840 - 11843 2014

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1359-7345

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An Experimental Study on the Processes of Hierarchical Morphology Replication by Means of a Mesocrystal: A Case Study of poly(3,4-ethylenedioxythiophene)

Yurika Munekawa, Yuya Oaki and Hiroaki Imai

Langmuir 30 ( 11 ) 3236 - 3242 2014

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0743-7463

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Bioinspired stiff and flexible composites of nanocellulose-reinforced amorphous CaCO3

Tsuguyuki Saito, Yuya Oaki, Tatsuya Nishimura, Akira Isogai and Takashi Kato

Materials Horizons 1   321 - 325 2014

Research paper (scientific journal), Joint Work, Accepted

Imaging of Accumulated Mechanical Stresses Using Self-Assembled Layered Conjugated Polymer

Mochizuki Y., Imai H., Oaki Y.

ACS Applied Materials and Interfaces (ACS Applied Materials and Interfaces)  15 ( 41 ) 48725 - 48735 2023.10

ISSN  19448244

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When mechanical stresses, such as tensile, compressive, and frictional stresses, are applied to objects by various motions, they are accumulated in materials. Conventional mechanoresponsive materials and sensors detect one-time applied stress. However, the accumulated stresses are not visualized or measured in previous works. The present study demonstrated imaging and sensing of not only one-time but also accumulated tensile, compressive, and frictional stresses. Polyurethane (PU) film was combined with 2D layered polydiacetylene (PDA), a stimuli-responsive color-changing polymer. PDA generally exhibits no color changes with the application of tensile and compression stresses because the molecular motion leading to the color change is not induced by such mechanical stresses. Here the versatile mechanoresponsiveness was achieved using a block copolymer guest partially intercalated in the layered PDA. As the interlayer and outerlayer segments interact with PDA and PU, respectively, the applied stresses to the film are transferred from PU to PDA via the block copolymer guest. The color changes of the film imaged and quantified the accumulated work depending on the number and strength of the applied multiple stresses such as tensile, compressive, and frictional stresses. The design strategy of materials and methodology of sensing can be applied to the development of new sensors for accumulated mechanical stresses in a wide range of length and strength scales.

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Fluorine-Free Substrate-Independent Superhydrophobic Coatings by Nanoarchitectonics of Polydispersed 2D Materials

Hikichi R., Tokura Y., Igarashi Y., Imai H., Oaki Y.

Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan)  96 ( 8 ) 766 - 774 2023.08

ISSN  00092673

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Fluorine-free superhydrophobic surfaces have been required to meet environmental regulations in recent years. A new nanoarchitectonics is required to achieve superhydrophobicity without using perfluoroalkyl compounds. In the present work, surface-modified exfoliated nanosheets with polydispersed sizes were utilized to prepare coatings with high surface roughness and low surface energy. Fluorine-free superhydrophobic surfaces were obtained by spray coating of surface-modified exfoliated nanosheets based on transition-metal oxides. The water contact angle (ªw) 166.0 « 0.5° is the highest compared with that of the fluorine-free substrate-independent coatings in previous reports. The significant factors related to ªw were studied using machine learning combined with our chemical insight in the small data obtained in the present work. The resultant superhydrophobic coatings exhibited unique properties, such as sliding of water droplets, superoleophilic behavior, recyclability, and durability. The present design strategy can be applied to development of various functional coatings using exfoliated 2D materials with polydispersity.

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Departmental characterization of structural and mechanical properties of crossed lamellae of a gastropod Murex pecten

Nishio N., Sugiyama S., Yoshimura T., Terasaki R., Takasaki M., Oaki Y., Sasaki T., Imai H.

CrystEngComm (CrystEngComm)  25 ( 29 ) 4213 - 4218 2023.07

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We characterized departmental variations of the hierarchical lamellar structures of whorls, a siphonal canal, and spines of shells of a gastropod Murex pecten (Venus comb) and compared their mechanical properties. The crossed lamellae are basically composed of bundled aragonite nanorods ∼20 nm wide that are elongated along the (110) plane. The main body, including whorls and a siphonal canal, consists of four- and three-layer crossed lamellae, and thin spines comprise double- and single-layered structures including strained and distorted lamellae. The macroscopic bending strength and nanoscopic hardness of the spines were found to be greater than those of the main body of the shell. The specific strained and distorted lamellar structures are deduced to contribute to the enhanced mechanical properties of the long and thin parts.

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Capacity-prediction models for organic anode-active materials of lithium-ion batteries: advances in predictors using small data

Tobita H., Namiuchi Y., Komura T., Imai H., Obinata K., Okada M., Igarashi Y., Oaki Y.

Energy Advances (Energy Advances)  2 ( 7 ) 1014 - 1021 2023.05

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Organic energy storage has attracted a lot of interest in enhancing performance and reducing the consumption of resources. If performance predictors are prepared, the exploration of new compounds can be accelerated without consumption of time, energy, and effort. In the present work, a new straightforward capacity predictor is constructed for the exploration of organic anode-active materials. Sparse modeling for small data (SpM-S) combining machine learning (ML) and our chemical insights was used to construct linear regression models of specific capacity. In our previous work, two predictors (models G1 and G2) were prepared using small datasets. However, the descriptors and prediction accuracy of these models were not validated. In the present work, a new improved model (model G3) has been constructed with the addition of new data. These three models were studied in terms of data science: namely, prediction accuracy, validity of the descriptors, amount of training data used, and effect of ML algorithms. The straightforward, generalizable, and interpretable model G3 can be applied to explore new organic anode-active materials. Moreover, these data-scientific approaches to model construction and validation can be used to explore new energy-related materials even with small data.

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Development of prediction model for cloud point of thermo-responsive polymers by experiment-oriented materials informatics

Hayakawa M., Sakano K., Kumada R., Tobita H., Igarashi Y., Citterio D., Oaki Y., Hiruta Y.

Polymer Chemistry (Polymer Chemistry)  14 ( 19 ) 2383 - 2389 2023.04

ISSN  17599954

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Thermo-responsive polymers having a lower critical solution temperature (LCST) have attracted attention for biological applications such as drug delivery, diagnosis, and coating materials. In recent years, research on predicting LCST by utilizing machine learning has been conducted. However, since these methods targeted only copolymers combining specific monomer structures, they are not versatile, and multiple trials are still required to obtain new thermo-responsive polymers with the desired LCST. In this study, a prediction model for cloud point temperature (TCP) was built by a combination of materials informatics and chemical insight, named sparse modeling for small data (SpM-S) using a small dataset of polymers collected from the literature as training data. This approach created a model that is interpretable, easy to calculate, and versatile. The prediction accuracy was validated using data from different literature sources and experimental test data. The model was able to predict the TCP of polymers containing monomers not included in the dataset as well as polymers containing monomers included in the dataset. The predictive model has the potential to guide the design of new thermo-responsive polymers, and to contribute to efficient development of thermo-responsive polymers.

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Enhanced and stabilized photoluminescence of perovskite cesium lead bromide nanocubes through ordered assemblies

Sasaki M., Hashimoto S., Iso Y., Oaki Y., Isobe T., Imai H.

Nanoscale Advances (Nanoscale Advances)  5 ( 9 ) 2553 - 2557 2023.04

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This work clarified the effects of self-assembly of perovskite cesium lead bromide (CsPbBr3) nanocubes (NCs) covered with didodecyldimethyl ammonium bromide (DDAB) on photoluminescence (PL) properties. Although the PL intensity of isolated NCs was weakened in the solid state even under inert conditions, the quantum yield of PL (PLQY) and the photostability of DDAB-covered NCs were drastically improved by the formation of two-dimensional (2D) ordered arrays on a substrate. The PLQY of the 2D arrays increased to ca. 60% by initial excitation illumination at 468 nm and was maintained for over 4000 h. The improved PL properties are attributable to the fixation of the surface ligand around the NCs in the specific ordered arrays.

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Construction of Millimeter-Wide Monolayers of Ordered Nanocubes as a Stain of “Wineglass Tears” Driven by the Marangoni Flow

Takatsuji Y., Matsumoto R., Sazaki G., Oaki Y., Imai H.

Langmuir (Langmuir)  39 ( 11 ) 4091 - 4099 2023.03

ISSN  07437463

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We constructed millimeter-wide monolayers consisting of tetragonally ordered BaTiO3 (BT) nanocubes through the liquid film formation caused by the Marangoni flow in a toluene-hexane binary liquid containing oleic acid. A thin liquid film containing BT nanocubes was overspread on a standing silicon substrate through the condensation of toluene at the advancing front after the preferential evaporation of hexane. Then, the oscillatory droplet formation like “wineglass tears” occurred on the substrate. Finally, two-dimensionally ordered BT nanocubes were observed as a stain of “wineglass tears” on the substrate after the liquid film receded through evaporation. The presence of a thin liquid film in the binary system is essential for the production of millimeter-wide monolayers on the substrate because multilayer deposition occurs without the formation of a thin liquid film in monocomponent systems. We improved the regularity of the ordered arrays of nanocubes by adjusting the liquid component and evaporation conditions.

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Stimuli-Responsive Sponge for Imaging and Measuring Weak Compression Stresses

Ono N., Seishima R., Okabayashi K., Imai H., Fujii S., Oaki Y.

Advanced Science (Advanced Science)  10 ( 3 )  2023.01

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Imaging and measuring compression stresses secure a safe and healthy life. Compression stresses in kPa range are not easily detected by conventional mechanoresponsive materials because microscopic molecular motion of the chromophores is not induced by such weak stresses. Moreover, imaging of the stress distribution is not achieved so far. The present study shows a sponge device combining two stimuli-responsive materials, a capsule releasing interior liquid and color-changing polymer in responses to compression stress and chemical stimulus, respectively. The stimuli-responsive capsule is dispersed on a melamine sponge comprised of the fibers with coating the layered polydiacetylene (PDA). The application of weak compression stresses induces collapse of the capsules, outflow of the interior liquid, and subsequent irreversible color change of PDA. The cascading response in the sponge device colorimetrically enables imaging of the distribution and measuring the strength of the compression stresses in kPa range. Furthermore, the device demonstrates imaging and measuring unknown weak compression stresses applied by the irregular-shaped objects. A couple of clinical issues in surgical operation of intestine are studied using the stress-imaging sponge device. The device and its design strategy can be applied to stress imaging in a variety of fields.

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A highly sensitive friction-imaging device based on cascading stimuli responsiveness

Shioda N., Kobayashi R., Katsura S., Imai H., Fujii S., Oaki Y.

Materials Horizons (Materials Horizons)  10 ( 6 ) 2237 - 2244 2023

ISSN  20516347

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Imaging and measurement of friction forces are required in a variety of fields. If the friction forces originating from the motions of professionals are quantitatively analyzed, the data can be applied to a motion-copying system by a robot. However, weak friction forces have not been visualized and quantified using conventional sensing materials and devices because of their low sensitivity. Here we present a highly sensitive friction-imaging device based on the cascading responses of stimuli-responsive materials, namely polydiacetylene (PDA) and dry liquid (DL). Weak friction forces disrupt the DL, which is composed of liquid droplets surrounded by solid particles. The outflowing liquid under chemical stress changes the color of PDA. The cascading responses enable colorimetric imaging and measurement of weak friction forces in the range of 0.006-0.080 N. Furthermore, the device visualizes the force distribution of handwriting in calligraphy depending on the individual characteristics of an expert, a practician, and a beginner. A high-sensitivity friction-imaging device can be used to understand various motions.

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Colloidally Stable Polypyrrole Nanoparticles Synthesized by Surfactant-Free Coupling Polymerization

Atsuta Y., Takeuchi K., Shioda N., Hamada W., Hirai T., Nakamura Y., Oaki Y., Fujii S.

Langmuir (Langmuir)   2023

ISSN  07437463

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Surfactant-free polypyrrole (PPy) nanoparticles, which were colloidally stable in aqueous medium, were successfully synthesized by coupling polymerization of pyrrole using Fe(NO3)3 solids in the absence of any colloidal stabilizer. The pyrrole monomers were gradually supplied from the vapor phase, and the coupling reaction of the monomers could proceed to generate PPy in a water medium. The resulting PPy nanoparticles were extensively characterized in terms of diameter, bulk chemical composition, surface chemistry, and colloidal stability by dynamic light scattering, electron microscopy, elemental microanalysis, Fourier transform infrared spectroscopy, Raman spectroscopy, electrophoresis, and X-ray photoelectron spectroscopy. The characterization results indicated that the PPy nanoparticles can be colloidally stable based on the electrostatic stabilization mechanism due to cationic charges generated on the PPy molecules by doping during the polymerization. General chemical oxidative polymerization in aqueous medium using the Fe(NO3)3 oxidant without a colloidal stabilizer as a control experiment resulted in generation of atypical PPy aggregates with over a micrometer size, indicating that the polymerization at low ionic strength is essential for colloidal particle formation. Finally, it was demonstrated that the PPy nanoparticles worked as a surfactant-free black-colored particulate emulsifier by adsorption at the oil-water interface to stabilize Pickering-type oil-in-water emulsions.

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Nanoscopic Force Sensitivity of Polydiacetylene 2D Layered Composites with Guest Molecules

Das B., Shioda N., Yagi S., Oaki Y., Sugihara K.

Advanced Materials Interfaces (Advanced Materials Interfaces)   2023

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2D polydiacetylene (PDA) layered composites with added guest molecules have demonstrated an excellent tunable mechanochromic properties toward the development of mechanochromic force sensors in energy-related and medical applications. However, its force sensitivity at the nanoscale is left uncharacterized due to a lack of technique to conveniently apply forces to the 2D films in different directions, limiting the quantitative understanding of the sensitivity-tuning mechanism. In this work, the quantitative friction force microscopy combined with fluorescence microscopy is introduced to measure the force sensitivity of the PDA layered composites with guest organic amines at the nanoscale. Intercalating nonylamine and 1-aminodecane increase the sensitivity of 10,12-pentacosadiynoic acid by 127% and 111%, respectively, whereas adding n-tridecaylamine and stearylamine reduce it by 77% and 86%. This force sensitivity at the nanoscale is inversely correlated to the thermochromic temperature and the Young's moduli of the films, suggesting that the softer film has both higher force- and thermo-sensitivity.

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Nanoarchitectonics of Exfoliated Flexible Nanosheet Based on Laterally Stacked Macrocycles

Shioda N., Heo J.M., Kim B., Imai H., Kim J.M., Oaki Y.

Advanced Materials Interfaces (Advanced Materials Interfaces)   2023

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2D nanostructures including monolayers and few layers exhibit unique properties originating from the anisotropic ultrathin nature. Conventional organic 2D nanostructures, such as covalent organic frameworks, are comprised of the planar π-conjugated macromolecules linked and extended parallel to the layers. The present work shows a new type of exfoliated organic 2D material. The macrocycles are stacked perpendicular to the lateral direction of the nanosheets. Self-assembly of a designed macrocyclic diacetylene monomer with a chair conformation forms the laminated structures containing the layers based on the perpendicularly arranged macrocycles. The exfoliable layered structures are obtained by the topochemical polymerization of the diacetylene moieties. The intercalation and subsequent swelling provide the nanosheets based on the laterally stacked macrocycles in aqueous phase. The colloidal nanosheets possess structural flexibility with the molecular motions originating from the ultrathin nature and conformational diversity. The hydrogel cross-linked with the flexible nanosheets exhibits unique stretching and thermoresponsive shrinking properties. The present work implies the potential of the flexible 2D materials based on the macrocycles.

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Ultrastructure of setae of a planktonic diatom, Chaetoceros coarctatus

Owari Y., Nakamura F., Oaki Y., Tsuda H., Shimode S., Imai H.

Scientific Reports (Scientific Reports)  12 ( 1 )  2022.12

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Silica frustules of most planktonic diatoms have many shallow holes in which the length (L) is smaller than the width (W). The present study focuses on a silica ultrastructure of setae of a planktonic diatom having deep (L/W > 1) holes. Here, we characterized microscopically patterned nanoholes on the silica walls of thick, robust, and hollow setae of a colony of Chaetoceros coarctatus. Basically, tetragonal poroid arrangements with and without a costa pattern are observed on the inner and outer surfaces, respectively, for three kinds of curving hollow setae attached to the anterior, intercalary, and posterior parts of the colony. The seta structures including specific poroid arrangements and continuity of deep nanoholes depend on the location. The deep nanoholes ∼90 nm wide are elongated from 150 to 1500 nm (L/W ∼17) with an increase in the wall thickness of the polygonal tubes of the setae. The inside poroid array, with a period of 190 nm in the extension direction of setae, is lined by parallel plates of the costae. However, the poroid arrangement on the outer surface is disordered, with several holes obstructed with increasing wall thickness of the posterior terminal setae. According to the movement of a colony in a fluid microchannel, the thick curving terminal setae is suggested to involve attitude control and mechanical protection. Using an optical simulation, the patterned deep through-holes on the intercalary setae were suggested to contribute anti-reflection of blue light in the wavelength range of 400 to 500 nm for the promotion of photosynthesis in seawater.

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Micro- and nanometric characterization of the celestite skeleton of acantharian species (Radiolaria, Rhizaria)

Fujimaki R., Suzuki N., Kimoto K., Nagai Y., Oaki Y., Shimode S., Toyofuku T., Imai H.

Scientific Reports (Scientific Reports)  12 ( 1 )  2022.12

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We clarified the specific micrometric arrangement and nanometric structure of the radiolarian crystalline spines that are not a simple single crystal. A body of the celestite (SrSO4) skeleton of acantharian Acanthometra cf. multispina (Acanthometridae) composed of 20 radial spines having four blades was characterized using microfocus X-ray computed tomography. The regular arrangement of three types of spines was clarified with the connection of the blades around the root of each spine. The surface of the spines was covered with a chitin-based organic membrane to prevent from dissolution in seawater. In the nanometric scale, the mesocrystalline structure that consists of nanoscale grains having distorted single-crystal nature was revealed using scanning- and transmission electron microscopies, electron diffraction, and Raman spectroscopy. The acantharian skeletons have a crystallographically controlled architecture that is covered with a protective organic membrane. These facts are important for penetrating the nature of biogenic minerals.

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Preparation of conductive Cu<inf>1.5</inf>Mn<inf>1.5</inf>O<inf>4</inf> and Mn<inf>3</inf>O<inf>4</inf> spinel mixture powders as positive active materials in rechargeable Mg batteries operative at room temperature

Takemitsu H., Hayashi Y., Watanabe H., Mandai T., Yagi S., Oaki Y., Imai H.

Journal of Sol-Gel Science and Technology (Journal of Sol-Gel Science and Technology)  104 ( 3 ) 635 - 646 2022.12

ISSN  09280707

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We prepared conductive mixtures of Cu1.5Mn1.5O4 and Mn3O4 spinels (CMO–MOs) as positive electrode active materials in rechargeable Mg batteries (RMBs) using a sol–gel complex polymerization method. The CMO–MO spinel mixtures with high specific surface areas above 100 m2 g−1 were obtained with mild calcination in Ar at 300 °C. The conductivity of CMO–MOs was estimated to be approximately 1000 times higher than that of a conventional MgMn2O4 (MMO) spinel powder. The discharge capacities evaluated using 2032-type coin-cell battery with a Mg-alloy negative electrode at room temperature increase with an increase in the specific surface area of the spinel powders. The specific surface area for providing the theoretical capacity of the conductive CMO–MOs was about one-third that of the insulative MMO. High specific surface area and high conductivity are key parameters for the positive active material to realize practical room-temperature operation of RMBs.

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Water Reduction Photocathodes Based on Ru Complex Dyes Covered with a Conjugated Polymer Nanosheet

Shimamura T., Kobayashi A., Oaki Y., Yoshida M., Kato M.

Energy and Fuels (Energy and Fuels)  36 ( 19 ) 11559 - 11566 2022.10

ISSN  08870624

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Water-splitting dye-sensitized photoelectrochemical cells are promising devices for resolving energy and environmental problems by producing H2, a clean energy source, from water and sunlight. However, their performance is still limited because of dye desorption from the electrode and their weak light-absorption efficiency. In this study, we fabricated two water-reducing photocathodes, NiO|RuCP/BQPy and NiO|RuCP-Zr-RuP/BQPy, by combining the layer-by-layer formation of mono- (RuCP) and bi- (RuCP and RuP with Zr4+cations) layer molecular films of Ru(II) dyes, respectively, on a p-type NiO substrate with the chemical vapor deposition of the nanosheet catalyst based on the BQPy organic polymer comprising benzoquinone and pyrrole moieties. These photocathodes produced H2under visible light irradiation and a small electrical bias in a 0.1 M Na2SO4aqueous solution (λ > 420 nm, 65 mW cm-2, E = -0.254 V versus normal hydrogen electrode, and pH 3). Both the photocurrent value and amount of H2produced by double-dye-layered NiO|RuCP-Zr-RuP/BQPy were smaller than those of NiO|RuCP/BQPy, probably because of the energy transfer inactivation between the Ru(II) dyes, which competes with the reductive quenching (i.e., electron injection) by NiO. Ru(II) dye desorption from the NiO|RuCP/BQPy photocathode was significantly reduced to approximately a third of that of NiO|RuCP, indicating that the deposited BQPy polymer improved the durability of the photocathode. The deposition of the BQPy polymer can be easily performed under mild conditions (60 °C in air); therefore, this technique shows great potential application for the construction of various types of dye-sensitized water-reducing photocathodes.

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Coatable 2D Conjugated Polymers Containing Bulky Macromolecular Guests for Thermal Imaging

Edagawa A., Matsuda S., Kawakubo H., Imai H., Oaki Y.

ACS Applied Materials and Interfaces (ACS Applied Materials and Interfaces)  14 ( 38 ) 43792 - 43801 2022.09

ISSN  19448244

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Dynamic properties are derived from the structural flexibility of 2D polymers. Softening layered structures has the potential for tuning and enhancing the dynamic properties. In the present work, the flexibility of layered polydiacetylene (PDA) is tuned by the interlayer polymeric guests with different branching structures. PDA shows thermoresponsive color-change properties through shortening the effective conjugation length with molecular motion. Whereas the blue-to-red color transition is observed at certain threshold temperatures for the layered PDA without the interlayer guest, the intercalation of the bulky polymer guests lowers the starting temperature and widens the temperature range for the thermoresponsive color changes. The resultant layered composite of PDA and bulky polymer affords the homogeneous coating on substrates on the centimeter scale. The thermoresponsive color-change coating is applied to temperature-distribution imaging. The specific heat of liquids is colorimetrically estimated using the coating on the bottle. The coating on a silk cloth visualizes the temperature distribution on a simulated tissue during surgical operation using an ultrasonic coagulation cutting device. The coating can be applied to thermal imaging in a variety of fields. Moreover, the softening strategy contributes to explore dynamic properties of soft 2D materials.

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Selective syntheses of thick and thin nanosheets based on correlation between thickness and lateral-size distribution

Haraguchi Y., Imai H., Oaki Y.

iScience (iScience)  25 ( 9 )  2022.09

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Exfoliation of layered materials, a typical route to obtain 2D materials, is not easily controlled because of the unpredictable downsizing processes. In particular, the thickness control remains as a complex challenge. Here, we found a correlation between the thickness and lateral size distribution of the exfoliated nanosheets, such as transition metal oxides and graphene oxide. The layered composites of the host metal oxides and interlayer organic guests are delaminated into the surface-modified nanosheets in organic dispersion media. The exfoliation behavior varies by combination of the hosts, guests, and dispersion media. Here, we found that the thick and thin nanosheets were obtained on the monodispersed and polydispersed conditions, respectively. The selective syntheses of the thick and thin nanosheets were achieved using a prediction model of the lateral size distribution. The correlation between the thickness and lateral size distribution can be applied to thickness-selective syntheses of 2D materials.

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Nanosheet-Based Uneven Thin Film Exhibiting Angle-Independent Structural Color and Its Application to Detection of Biogenic Amines

Haraguchi Y., Imai H., Oaki Y.

Advanced Materials Interfaces (Advanced Materials Interfaces)  9 ( 25 )  2022.09

ISSN  2196-7350

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Anisotropic ultrathin 2D materials are used as building blocks to obtain higher-order structures. Tailoring the size, surface chemistry, and assembly state of exfoliated nanosheets is required for the design of functional materials. However, these factors are not easily controlled during the down-sizing exfoliation process, which is a general route for obtaining 2D materials. In the present work, polydispersed nanosheets of a transition metal oxide are prepared based on prediction model for the size distribution constructed by a combination of machine learning and chemical perspective on small data. Self-assembly of the exfoliated nanosheets results in the uneven thin films exhibiting an angle-independent structural color. As the nanosheets vary in thickness and lateral size, their assembled thin films exhibit structural color independent of the incident angle. The structural color is changed by casting only 20 µL of an aqueous solution containing biogenic amines such as histamine within a sensing time of 5 min. The biogenic amines are intercalated into the interlayer space of the stacked nanosheets and the resulting increase in the thickness changes the color of the thin-film device. The new design strategies can be applied to constructing other thin-film sensing devices based on nanosheets.

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Layered macrocycles with flexibility and tunable dynamic properties for wide-range thermoresponsive color changes

Shioda N., Heo J.M., Kim B., Imai H., Kim J.M., Oaki Y.

Sensors and Diagnostics (Sensors and Diagnostics)  1 ( 1 ) 160 - 168 2022.08

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Layered materials exhibit unique properties, such as intercalation and exfoliation, originating from the two-dimensional anisotropic nanostructures. A variety of inorganic and organic layered materials have been synthesized for design of functions. However, conventional host layers are static and rigid to induce dynamic functions originating from the structural flexibility. The present work shows a new dynamic and flexible host layer based on organic macrocycles. A macrocycle containing functional, flexible, and intercalating units, namely macrocyclic diacetylene (MCDA), was designed to form a self-assembled layered structure. After the guest molecules were intercalated in the interlayer space, the host MCDA layers were topochemically polymerized to obtain polydiacetylene. The layered macrocycles containing the π-conjugated main chain and interlayer guests showed gradual thermoresponsive color changes in a wide temperature range of −100 to 230 °C with variation of the effective conjugation length. The flexible host layer affords induction of the dynamic motion of the intrinsically rigid π-conjugated main chain in the wide temperature range. Moreover, the thermo-responsivity was tuned by the intercalated guests. The color-change properties enabled real-time temperature imaging for medical applications. Flexible layered macrocycles can be a new design strategy of soft materials with dynamic functions.

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A Capacity-Prediction Model for Exploration of Organic Anodes: Discovery of 5-Formylsalicylic Acid as a High-Performance Anode Active Material

Komura T., Sakano K., Igarashi Y., Numazawa H., Imai H., Oaki Y.

ACS Applied Energy Materials (ACS Applied Energy Materials)  5 ( 7 ) 8990 - 8998 2022.07

ISSN  2574-0962

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Development of high-performance organic energy storage is one of the important challenges in recent materials science. Molecular design and synthesis have potential for enhancement of the performances. Efficient exploration and design of the molecules are required in a wide search space. In the present work, a capacity prediction model for organic anodes was constructed on small experimental data by sparse modeling, a method of machine learning, combined with our chemical insights. The straightforward linear regression model facilitated discovery of a high-performance active material for organic anodes in a limited number of experiments. A recommended compound, 5-formylsalicylic acid (SA-CHO), showed one of the highest performances in recent works, i.e., a specific capacity of 873 mA h g-1at 100 mA g-1(sample number: n = 3) with rate performance and cycle stability. The model can be applied to explore organic anode active materials with higher specific capacity.

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Nanoarchitectonics for conductive polymers using solid and vapor phases

Oaki Y., Sato K.

Nanoscale Advances (Nanoscale Advances)  4 ( 13 ) 2773 - 2781 2022.04

ISSN  2516-0230

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Conductive polymers have been extensively studied as functional organic materials due to their broad range of applications. Conductive polymers, such as polypyrrole, polythiophene, and their derivatives, are typically obtained as coatings and precipitates in the solution phase. Nanoarchitectonics for conductive polymers requires new methods including syntheses and morphology control. For example, nanoarchitectonics is achieved by liquid-phase syntheses with the assistance of templates, such as macromolecules and porous materials. This minireview summarizes the other new synthetic methods using the solid and vapor phases for nanoarchitectonics. In general, the monomers and related species are supplied from the solution phase. Our group has studied polymerization of heteroaromatic monomers using the solid and vapor phases. The surface and inside of solid crystals were used for the polymerization with the diffusion of the heteroaromatic monomer vapor. Our nanoarchitectonics affords to form homogeneous coatings, hierarchical structures, composites, and copolymers for energy-related applications. The concepts using solid and vapor phases can be applied to nanoarchitectonics for not only conductive polymers but also other polymers toward a variety of applications.

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Performance Predictors for Organic Cathodes of Lithium-Ion Battery

Sakano K., Igarashi Y., Imai H., Miyakawa S., Saito T., Takayanagi Y., Nishiyama K., Oaki Y.

ACS Applied Energy Materials (ACS Applied Energy Materials)  5 ( 2 ) 2074 - 2082 2022.02

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Organic cathodes for lithium-ion batteries are one of the most promising and significant materials toward a sustainable society. The molecular design is a key to achieve superior performances beyond inorganic cathodes. The present work shows predictors of the reaction potential, specific capacity, and ideal energy density for organic cathodes. Straightforward prediction models of the performance were constructed by a combination of machine learning and chemical insight, namely, sparse modeling for small data (SpM-S), on a small data set as training data found in the literature. The prediction accuracy was validated using different literature data. The predictors can be applied to explore high-performance organic cathodes in a wide search space efficiently. Moreover, SpM-S afforded straightforward, interpretable, and generalizable prediction models compared to other machine-learning algorithms. The small-data-driven methodology can be applied for further exploration of materials, enhancement of performances, and optimization of processes.

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Designed nanostructures created via physicochemical switching of the growth mode between single crystals and mesocrystals†

Kanazawa S., Oaki Y., Imai H.

Nanoscale Advances (Nanoscale Advances)  4 ( 6 ) 1538 - 1544 2022.02

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Most biominerals are composed of mesocrystals, in which individual nanoparticle building units have a defined long-range order on the atomic scale in at least one direction. Although the crystal size and orientation of the mesostructures are spatially designed in biological architectures, it has been difficult to achieve adequate control of the crystal growth to produce modulated mesostructures in artificial aqueous systems. Here, we propose a simple physicochemical approach for the spatial design of nanostructures using an aqueous solution system. The ordered arrays of oriented fluorapatite (FA) rods similar to tooth enamel are produced on a polymer substrate in a supersaturated solution. We succeeded in reversible switching of the growth mode of FA between single-crystalline rods and mesocrystalline grains through the disturbance of the solution. The primary crystal size was tuned between micrometric rods ∼0.5 μm wide and >5 μm long and nanoscale grains ∼10 nm wide and 50 nm long without a drastic change in the c direction. Hierarchical architectures consisting of iso-oriented FA microrods and nanograins were constructed via temporal control of the crystal growth mode by switching a physicochemical parameter, such as the degree of supersaturation at the growth front.

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Sparse modeling for small data: case studies in controlled synthesis of 2D materials

Haraguchi Y., Igarashi Y., Imai H., Oaki Y.

Digital Discovery (Digital Discovery)  1 ( 1 ) 26 - 34 2022.02

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Data-scientific approaches have permeated into chemistry and materials science. In general, these approaches are not easily applied to small data, such as experimental data in laboratories. Our group has focused on sparse modeling (SpM) for small data in materials science and chemistry. The controlled synthesis of 2D materials, involving improvement of the yield and control of the size, was achieved by SpM coupled with our chemical perspectives for small data (SpM-S). In the present work, the conceptual and methodological advantages of SpM-S were studied using real experimental datasets to enable comparison with other machine learning (ML) methods, such as neural networks. The training datasets consisted of ca. 40 explanatory variables (xn) and 50 objective variables (y) regarding the yield, size, and size-distribution of exfoliated nanosheets. SpM-S provided more straightforward, generalizable, and interpretable prediction models and better prediction accuracy for new experiments as an unknown test dataset. The results indicate that machine learning coupled with our experience, intuition, and perspective can be applied to small data in a variety of fields.

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Electroless nickel plating on a biomineral-based sponge structure

Takeoka H., Seike M., Nakamura Y., Imai H., Oaki Y., Fujii S.

Materials Advances (Materials Advances)  3 ( 2 ) 931 - 936 2022.01

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A 3-dimensional polypyrrole-palladium nanocomposite material was prepared by transferring a sponge structure of a sea urchin spine via chemical oxidative polymerization. The nanocomposite material was successfully coated with nickel, maintaining the 3-dimensional sponge structure by electroless plating in an aqueous medium.

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Demonstrated gradual evolution of disorder in crystalline structures between single crystal and polycrystal via chemical and physicochemical approaches

Kanazawa S., Oaki Y., Imai H.

CrystEngComm (CrystEngComm)  24 ( 25 ) 4546 - 4550 2022

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Various biological and biomimetic minerals are composed of mesocrystals, in which nanoscale crystalline units are ordered in approximately the same crystallographic direction. However, the variation of the crystallographic regularity of mesocrystals has not been clarified using experimental evidence. This work demonstrated the gradual evolution of disorder in crystalline structures between single crystal and polycrystal by monitoring the crystallographic regularity using electron diffraction patterns. Single-crystal rods of fluorapatite elongated in the c direction are switched to mesocrystals consisting of iso-oriented nanorods by adding a specific molecule having a carboxy group (chemical approach) and to roughly arranged nanograins by increasing the degree of supersaturation at the growth front (physicochemical approach). Lateral and vertical miniaturization of the growth units is achieved through stepwise nucleation and near-epitaxial growth. The crystallographic regularity gradually decreases with deviation of the c axis and rotation of the a axes through reduction of the growth unit size. Here we can tune the disorder in crystalline structures via the chemical and physicochemical approaches.

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Characterization of calcite spines of planktonic foraminifers (Globigerinidae)

Izumida K., Takasaki M., Fujimaki R., Nagai Y., Oaki Y., Naito K., Tanaka Y., Shimode S., Toyofuku T., Imai H.

CrystEngComm (CrystEngComm)  24 ( 13 ) 2446 - 2450 2022

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Calcitic spines ∼1 μm in diameter are projecting from a trochospiral test of a spinose planktonic foraminifer. According to electron diffraction, Raman spectra, and detailed electron microscope observation, the spines were found to be a single-crystal-like calcite that has a nanogranular texture containing microstrain. An organic envelope protects the biogenic calcite against dissolution in water. Their unique mechanical and chemical properties are ascribed to the specific micro- and nanoscopic structures. This journal is

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A nonclassical pathway to biomimetic strained SrSO<inf>4</inf> crystals

Fujimaki R., Oaki Y., Imai H.

CrystEngComm (CrystEngComm)  24 ( 24 ) 4356 - 4360 2022

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Biomimetic strained SrSO4 crystals were produced through a nonclassical pathway involving fiber-by-fiber accumulation with poly(acrylic acid) in an aqueous solution system. Polymer-stabilized fibrous hydrate crystals 20-40 nm wide and several micrometers long were formed in the initial stage. Spindle-shaped microrods of SrSO4 were then constructed by oriented attachment of the hydrous fibrils and subsequent dehydration. The strained structure of the anhydrous SrSO4 crystals is similar to biogenic SrSO4 spines of acantharian species, a marine unicellular holoplanktonic protist.

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Preparation of titania with double band structure derived from a quantum size effect: Drastic increase in the photocatalytic activity

Somekawa S., Watanabe H., Ono Y., Oaki Y., Imai H.

Materials Letters (Materials Letters)  304 2021.12

ISSN  0167577X

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Titania is a competent photocatalyst widely used in environmental purification. Unfortunately, its photocatalytic ability to generate hydrogen by water decomposition without a co-catalyst is poor. Here, an efficient enhancement of noble-metal-free photocatalytic activity was studied on the basis of titania prepared in a supermicroporous silica template using TiCl3 aqueous solution as a precursor. The amount of evolved hydrogen increased sharply by 37 times as the concentration of TiCl3 was increased from 5 to 10 wt%. The existence of two species of titania was determined by XAFS analysis at concentrations of 10 wt% or greater. It is suggested that titania quantum dots inside the supermicropores and titania particles outside the supermicropores were prepared at the optimum precursor concentration and the resultant composite band structures suppressed electron–hole recombination.

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A Layered Polydiacetylene Containing Hydrogen-Bonding 4,4′-Bipyridyl Guests: Reversible Color Changes with a Wide-Range Temperature Response

Mochizuki Y., Imai H., Oaki Y.

ChemPlusChem (ChemPlusChem)  86 ( 12 ) 1563 - 1568 2021.12

ISSN  2192-6506

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Layered organic polymers have intercalation capabilities and dynamic properties. In classical intercalation chemistry, the interlayer guests are intercalated in the host layers via electrostatic interaction. The present work shows the organic layered materials with the host-guest interlayer interaction via hydrogen bond. Polydiacetylene (PDA) exhibits color changes from blue to red with the application of external stimuli, such as thermal and mechanical stresses. Here we report on a layered PDA containing 4,4′-bipyridyl in the interlayer space as a hydrogen-bonding guest. Whereas the layered PDA without interlayer guest shows the color transition at 65 °C, gradual color changes with two-stage reversibility are observed in the temperature range of −20–240 °C by the introduction of the hydrogen-bonding guest. The weaker interlayer interaction via the hydrogen bond promotes the dynamic motion directing the thermoresponsive color changes in a wide temperature range.

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Cellulose intrafibrillar mineralization of biological silica in a rice plant

Nakamura E., Ozaki N., Oaki Y., Imai H.

Scientific Reports (Scientific Reports)  11 ( 1 )  2021.12

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The essence of morphological design has been a fascinating scientific problem with regard to understanding biological mineralization. Particularly shaped amorphous silicas (plant opals) play an important role in the vital activity in rice plants. Although various organic matters are associated with silica accumulation, their detailed functions in the shape-controlled mineralization process have not been sufficiently clarified. In the present study, cellulose nanofibers (CNFs) were found to be essential as a scaffold for silica accumulation in rice husks and leaf blades. Prior to silicification, CNFs ~ 10 nm wide are sparsely stacked in a space between the epidermal cell wall and the cuticle layer. Silica nanoparticles 20–50 nm in diameter are then deposited in the framework of the CNFs. The shape-controlled plant opals are formed through the intrafibrillar mineralization of silica nanoparticles on the CNF scaffold.

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Efficient photocatalytic conversion of benzene to phenol on stabilized subnanometer WO<inf>3</inf>quantum dots

Ohno A., Watanabe H., Matsui T., Somekawa S., Tomisaki M., Einaga Y., Oaki Y., Imai H.

Catalysis Science and Technology (Catalysis Science and Technology)  11 ( 19 ) 6537 - 6542 2021.10

ISSN  20444753

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Band engineering with a quantum size effect is proposed to be utilized to design photocatalytic activity for the conversion of organic compounds. Subnanometer WO3 quantum dots (QDs) are spontaneously produced with the enhancement of the photocatalytic activity in a mesoporous silica matrix by preliminary photochemical dissolution. An appropriate upshift of the conduction band of subnanometer WO3 QDs stabilized by the coverage with the surface WO bonds promotes the efficient conversion of benzene to phenol without decomposition of the product into CO2 under ultraviolet illumination.

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Size-Distribution Control of Exfoliated Nanosheets Assisted by Machine Learning: Small-Data-Driven Materials Science Using Sparse Modeling

Haraguchi Y., Igarashi Y., Imai H., Oaki Y.

Advanced Theory and Simulations (Advanced Theory and Simulations)  4 ( 10 )  2021.10

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2D materials exhibit emergent properties originating from their characteristic nanostructures. In general, monolayered and few-layered nanosheets are obtained by exfoliation of the precursor layered materials. However, lateral-size distribution of the nanosheets is not easily controlled through the exfoliation because of the unpredictable down-sizing processes. The present work shows selective syntheses of transition-metal-oxide nanosheets with the monodisperse and polydisperse lateral sizes by the assistance of machine learning on small experimental data. The precursor layered composites of host transition-metal oxides and interlayer organic guests are exfoliated into the surface-modified nanosheets in organic dispersion media. A prediction model of the size distribution is constructed by sparse modeling, a method of machine learning, on the experimental data. The host-guest-medium combinations achieving the monodisperse and polydisperse lateral sizes are recommended by the prediction model. Therefore, the nanosheets with the controlled lateral-size distribution are selectively obtained in a limited number of the experiments. Moreover, self-assembly of the polydispersed nanosheets forms the homogeneous thin film exhibiting interference color. The prediction model and its construction method can be applied to the other 2D materials. Moreover, the present work implies that sparse modeling is an effective approach for small-data-driven materials science.

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Yield-prediction models for efficient exfoliation of soft layered materials into nanosheets

Noda K., Igarashi Y., Imai H., Oaki Y.

Chemical Communications (Chemical Communications)  57 ( 48 ) 5921 - 5924 2021.06

ISSN  13597345

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Yield-prediction models were studied for efficient exfoliation of soft layered materials stackedviavan der Waals interactions with the assistance of machine learning on small experimental data. High-yield exfoliation of graphite and layered organic polymer was achieved under the conditions guided by the models in a limited number of experiments.

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Wide-area multilayered self-assembly of fluorapatite nanorods vertically oriented on a substrate as a non-classical crystal growth

Hagiwara Y., Oaki Y., Imai H.

Nanoscale (Nanoscale)  13 ( 21 ) 9698 - 9705 2021.06

ISSN  20403364

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Oriented attachment of homogeneously shaped nanoblocks, such as nanocubes and nanorods, is attracting attention as a fundamental process of non-classical crystal growth to produce specific ordered architectures of functional materials. Although lateral alignments of horizontally oriented nanorod are commonly observed at the air-liquid and liquid-solid interfaces in dispersion systems, the accumulation of vertically oriented nanorods on a substrate has rarely been produced in a wide area over a millimeter-sized flat surface. Here, we achieved homogeneous stacking of vertical fluorapatite nanorods with a large aspect ratio (~6) in a toluene-hexane mixture system through a gradual decrease in the dispersibility. Micrometer-thick flat films in which the c direction of fluorapatite nanorods was arranged perpendicularly to the surface were deposited on a substrate with a diameter of over 20 mm. The wide-area accumulation of vertical nanorods occurs through the self-assembly of laterally arranged clusters of nanorods covered with a stabilizing agent and subsequent gentle sedimentation on the substrate surface. This journal is

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Self-Assembly of 2D Nematic and Random Arrays of Sterically Stabilized Nanoscale Rods with and without Evaporation

Tago M., Takasaki M., Tokura Y., Oaki Y., Imai H.

Langmuir (Langmuir)  37 ( 21 ) 6533 - 6539 2021.06

ISSN  07437463

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The adequate manipulation of nanometer-scale building blocks using dispersion systems is regarded as a fundamental technique to fabricate elaborate microstructures. Although a liquid flow with evaporation is generally regarded as an essential factor for the self-assembly of floating blocks, experimental evidence has not been sufficient to clarify the importance of the flow in the dispersion systems. In the present study, 2D nematic layers of sterically stabilized nanoscale calcite rods were achieved in a millimeter-scale region on a solid substrate via the very slow recession of an organic dispersion with evaporation. 2D random arrays of the nanorods were obtained via recession of the liquid in the same system without evaporation. When the nanorods were not sterically stabilized, 3D random arrays were formed even with evaporation. We demonstrated that the evaporation-driven flow of sterically stabilized nanorods to a confined space at the air-liquid-solid interface is essential for the formation of 2D nematic structures on a substrate.

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Morphological study of fibrous aragonite in the skeletal framework of a stony coral

Sugiura M., Yasumoto K., Iijima M., Oaki Y., Imai H.

CrystEngComm (CrystEngComm)  23 ( 20 ) 3693 - 3700 2021.05

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Calcareous skeletons of stony corals are composed of a low-crystalline core (center of calcification: COC) and surrounding fibrous crystals. We characterized the overall framework of juvenile Acropora digitifera corals to clarify the entire calcic architecture and the contribution of abiotic processes. Skeletal and tubular frameworks contain string and sheet COCs, respectively, consisting of strained aragonite nanograins. Parallel and curved structures of fibrous aragonite develop around the COC cores through geometric selection and a gradual change in the growth direction of the c-direction-elongated nanorods. Based on a study of the nanoscale morphology of the coral frameworks by comparing them to fibrous crystals grown in artificial systems, it appears that subsequent precipitation of the fibrous aragonite on the COC is primarily regulated by environmental abiotic parameters. The architecture of the COC network is deduced to be designed biologically and then thickened by the fibrous crystals that are produced with morphology formation through physicochemical processes although the vital activity controls the total mineralization.

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Morphological evolution of carbonated hydroxyapatite to faceted nanorods through intermediate states

Hagiwara Y., Takasaki M., Oaki Y., Imai H.

CrystEngComm (CrystEngComm)  23 ( 16 ) 2968 - 2972 2021.04

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Pure and carbonated hydroxyapatite (HA) nanocrystals are regarded as capital biocompatible materials. However, the formation process for faceted nanorods of HA has not been sufficiently clarified in supersaturated aqueous solution systems. Here, we monitored morphological evolution of carbonated HA to faceted crystals on the conversion of a parent calcite nanocrystal under hydrothermal conditions. In the initial stage, low-crystalline carbonated HA nanosheets ∼5 nm thick are formed as metastable intermediates. In the progressive stage, faceted nanorods ∼50 nm wide and ∼200 nm long grow as a relatively stable form of HA through the intermediates. The morphological evolution is ascribed to a stabilizing process of HA for improvement of the crystallinity and a decrease in the specific surface area and carbonate content.

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Ultrahigh-Sensitive Compression-Stress Sensor Using Integrated Stimuli-Responsive Materials

Nakamitsu M., Oyama K., Imai H., Fujii S., Oaki Y.

Advanced Materials (Advanced Materials)  33 ( 14 )  2021.04

ISSN  09359648

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Measurement of mechanical stresses, such as compression, shear, and tensile stresses, contributes toward achieving a safer and healthier life. In particular, the detection of weak compression stresses is required for healthcare monitoring and biomedical applications. Compression stresses in the order of 106–1010 Pa have been visualized and/or quantified using mechano-responsive materials in previous works. However, in general, it is not easy to detect compression stresses weaker than 103 Pa using conventional mechano-responsive materials because the dynamic motion of the rigid mechano-responsive molecules is not induced by such a weak stress. In the present work, weak compression stresses in the order of 100–103 Pa are visualized and measured via the integration of stimuli-responsive materials, such as layered polydiacetylene (PDA) and dry liquid (DL), through response cascades. DLs consisting of liquid droplets covered by solid particles release the interior liquid and collapse with application of a weak compression stress. The color of the layered PDA is changed by the spilled liquid as a chemical stress. A variety of weak compression stresses, such as expiratory pressure, are visualized and colorimetrically measured using the paper-based device of the integrated stimuli-responsive materials. Diverse mechano-sensing devices can be designed via the integration of stimuli-responsive materials.

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Effective 3D open-channel nanostructures of a MgMn<inf>2</inf>O<inf>4</inf>positive electrode for rechargeable Mg batteries operated at room temperature

Sone K., Hayashi Y., Mandai T., Yagi S., Oaki Y., Imai H.

Journal of Materials Chemistry A (Journal of Materials Chemistry A)  9 ( 11 ) 6851 - 6860 2021.03

ISSN  20507488

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Room-temperature operations of rechargeable Mg coin-cell batteries have been achieved using a Mg alloy negative electrode and a spinel MgMn2O4(MMO)-positive electrode. The present work focuses on clarifying the effects of the physiochemical properties of the MMO powder including the specific surface area (SBET) and porosity of the positive electrode on Mg battery performances in practical applications. Finally, optimal specific surface area and porosity parameters were obtained that ensured excellent battery performances as a standard coin-cell at room temperature. A typical MMO powder synthesized using a modified sol-gel method with propylene oxide-driven complex polymerization had a largeSBET> 200 m2g−1, and more than 90% porosity with a triple-tiered 3D open-channel network. Here we evaluated the discharge capacity and the cyclability for room-temperature operation as a function ofSBETin a full cell with a Mg negative electrode as well as half cells with a carbon graphite electrode. Irrespective of whether half cells or a full cell was used, the initial discharge capacity was found to depend linearly on theSBETof the porous MMO powder in a Mg tetrakis(hexafluoroisopropyl)borate/triglyme electrolyte with a wide potential window, ΔE> 3.6 V. Eventually, the maximum discharge capacity of 220 mA h g−1was realized at 25 °C in the full cell using the 3D open-channel nanostructure withSBET= 236 m2g−1. The cyclability in the full cell with the Mg alloy negative electrode, however, degraded with the increasingSBET, while no cyclability degradation was observed in the half cell with the carbon electrode. A possible mechanism is discussed regarding passivation of the Mg alloy electrode in discharge/charge cycles.

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Lateral-size control of exfoliated transition-metal-oxide 2D materials by machine learning on small data

Mizuguchi R., Igarashi Y., Imai H., Oaki Y.

Nanoscale (Nanoscale)  13 ( 6 ) 3853 - 3859 2021.02

ISSN  20403364

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A wide variety of nanosheets including monolayers and few-layers have attracted much interest as two-dimensional (2D) materials for the unique anisotropic structures and properties. On the other hand, one of the significant remaining and challenging issues is the lateral-size control. Since 2D materials are generally synthesized by the exfoliation of layered materials, the lateral size is not easily controlled in the breaking-down processes. The experimental factors have not been found for the control and prediction. In the present work, lateral sizes of the exfoliated transition-metal-oxide nanosheets were predicted and controlled by the assistance of machine learning. Layered composites of host inorganic layers and guest organic molecules were exfoliated into nanosheets in organic dispersion media. The lateral size of the nanosheets was estimated by dynamic light scattering (DLS), instead of microscopy methods, to achieve high-throughput analyses. Factors governing the lateral size are explored on the small experimental data by the assistance of sparse modeling, a method of machine learning. The eight physicochemical parameters of the organic guests and dispersion media were extracted by sparse modeling for the construction of the size-prediction model. The size-prediction model accelerated the selective syntheses of the nanosheets with large and small lateral sizes in a limited number of experiments. The results indicate that the prediction model is a guideline to find suitable exfoliation conditions for size control. Size-selective syntheses of a variety of 2D materials can be achieved by similar methods using sparse modeling on small experimental data. Moreover, sparse modeling is applicable to control the design and exploration of other materials and their processing based on small data. This journal is

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Diatom-mimetic channeled mesoporous silica membranes: Self-organized formation of a hierarchical porous framework

Kitamura R., Watanabe H., Somekawa S., Ono Y., Owari Y., Oaki Y., Imai H.

Materials Chemistry Frontiers (Materials Chemistry Frontiers)  5 ( 2 ) 862 - 868 2021.01

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Silica membranes having macrochannels with mesoporous walls were spontaneously fabricated using a self-organized process with rapid gelation of concentrated silicate and surfactant precursor solutions. The specific hierarchical porous framework consisting of straight macrochannels ca. 1 μm in diameter is similar to that of a biological silica frustule of diatoms. We applied the diatom-mimetic channeled mesoporous silica membranes to high-permeability-rate filtration and enhanced photocatalytic systems. The presence of macrochannels was found to improve the performance of the mesoporous silica membranes in filtration and as a photocatalyst carrier.

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Materials informatics for 2d materials combined with sparse modeling and chemical perspective: Toward small-data-driven chemistry and materials science

Oaki Y., Igarashi Y.

Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan)  94 ( 10 ) 2410 - 2422 2021

ISSN  00092673

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Application of data-scientific approaches to conventional sciences, such as chemo-informatics, bio-informatics, and materials informatics (MI), has attracted much interest toward datadriven research. The concept enables accelerated discovery of new materials, enhancement of performance, and optimization of processes. However, sufficient bigdata is not always prepared to apply to machine learning. For example, experimental scientists have their own small data including success and failure in their laboratory, whether in academia or industry. If such small data is effectively utilized with a data-scientific approach, research activities can be accelerated without energy, resource, and cost consumption. This account focuses on MI for small data, a recent concept for application of small data, with introduction of model cases, such as control of exfoliation processes to obtain 2D materials. Combination of machine learning and chemical perspective is effective for construction of straightforward and interpretable predictors through the extraction of a limited number of descriptors from small dataset. Although the prediction accuracy is not so precise, the model has enough accuracy to be a guideline reducing the number of the next experiments. The present MI for small data opens potentials of small-data-driven chemistry and materials science.

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Exfoliation chemistry of soft layered materials toward tailored 2D materials

Oaki Y.

Chemistry Letters (Chemistry Letters)  50 ( 2 ) 305 - 315 2021

ISSN  03667022

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Exfoliation of layered materials provides nanosheets, such as monolayers and few-layers. In recent years, nanosheets have attracted much interest as two-dimensional (2D) materials for their diverse properties and applications originating from the anisotropic characteristic structures. Exfoliation methods have been developed depending on the types of interactions between the layers, such as van der Waals and electrostatic interactions. The present review focuses on exfoliation chemistry based on rigid and soft natures of the layered materials. The rigid inorganic layered compounds are converted to the soft layered materials with interaction of organic guests. The surface-functionalized nanosheets are obtained by exfoliation of the soft layered composites with dispersion in organic media. The exfoliation behavior is governed by the flexibility of the precursor layered materials, i.e. interaction between the interlayer guest and dispersion medium. Although exfoliation is generally an uncontrollable top-down process, materials informatics on our own experimental small data assists elucidation of the control factors toward tailored 2D materials. The exfoliation schemes are applied to a variety of layered materials. The present review shows potential new insights for exfoliation chemistry of soft layered materials.

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Strained calcite crystals from amorphous calcium carbonate containing an organic molecule

Sugiyama S., Takasaki M., Oaki Y., Imai H.

CrystEngComm (CrystEngComm)  22 ( 42 ) 7054 - 7058 2020.11

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Amorphous calcium carbonate (ACC) is regarded as an important precursor of biogenic crystal phases having specific shapes and mechanical properties. In the present work, calcite that was produced from ACC nanoparticles containing aspartic acid was characterized by Raman scattering spectroscopy and nanoindentation techniques. The tensile strain of the calcite lattice that was estimated from the vibrational spectroscopy varied with the organic content and the mild calcination condition of ACC nanoparticles. Calcite was found to be hardened by the presence of residual organic components inside the crystal lattice. On the other hand, the modulus of calcite decreased as the content of external organic components increased. Here, the mechanical properties of the calcite framework are successfully tuned by the crystallization of the specific amorphous phases containing organic molecules. The mechanical modulation of calcite can be associated with lattice expansion by using vibrational spectroscopy. This journal is

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Intercalation and flexibility chemistries of soft layered materials

Oaki Y.

Chemical Communications (Chemical Communications)  56 ( 86 ) 13069 - 13081 2020.11

ISSN  13597345

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Layered materials, alternate stackings of two or more components, are found in a wide range of scales. Chemists can design and synthesize layered structures containing functional units. The soft-type layered materials exhibit characteristic dynamic functions originating from two-dimensional (2D) anisotropy and structure flexibility. This feature article focuses on "intercalation"and "flexibility"as two new perspectives for designing soft layered materials. Intercalation of guests is a characteristic approach for design of layered structures. Flexibility is an important factor to control the dynamic functions of the layered structures. As a model case, the intercalation-induced tunable stimuli-responsive color-change properties of layered polydiacetylene (PDA) are introduced to study the impact of the intercalation and flexibility on the dynamic functions. Recently, layered materials have drastically expanded the research area from conventional rigid inorganic compounds to new self-assembled nanostructures consisting of organic components, such as polymers, metal-organic frameworks, and covalent-organic frameworks. These new layered architectures have potentials for exhibiting dynamic functions originating from the structure flexibility beyond the static properties originating from classical intercalation and host-guest chemistries. Therefore, intercalation and flexibility chemistries of soft layered materials are regarded as new perspectives for design of advanced dynamic functional materials. This journal is

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Solid-State Low-Temperature Thermoresponsive and Reversible Color Changes of Conjugated Polymer in Layered Structure: Beyond Infrared Thermography

Watanabe K., Imai H., Oaki Y.

Small (Small)  16 ( 41 )  2020.10

ISSN  16136810

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Emergence of thermoresponsive and reversible color changes at low temperature is a challenging target. In general, it is not easy to induce sufficient dynamic motion of rigid molecules including chromophore at a lower temperature. The present work shows unusually low-temperature color-change properties originating from the dynamic motion of rigid conjugated polymer in solid state. The layered composites of polydiacetylene (PDA) and guest l-arginine (L-Arg) (PDA-(L-Arg)) exhibit temperature-responsive gradual color changes with reversibility in the range of 123–333 K in solid crystalline state. The dynamic properties are induced by gradual and reversible distortion of the π-conjugated main chain in response to temperature. The tuned flexibility of the layered structure facilitates motion of the rigid π-conjugated molecule at low temperature. The PDA-(L-Arg)-coated substrates are applied to visualization and quantification of 2D and 3D temperature distributions generated by cooling with liquid nitrogen. These thermographic devices afford to image lower temperature range than typical infrared thermography. The present work indicates potentials of layered architectures with tunable flexibility for emergence of dynamic properties.

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Amorphous flexible covalent organic networks containing redox-active moieties: A noncrystalline approach to the assembly of functional molecules

Suzuki J., Ishizone A., Sato K., Imai H., Tseng Y.J., Peng C.H., Oaki Y.

Chemical Science (Chemical Science)  11 ( 27 ) 7003 - 7008 2020.07

ISSN  20416520

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The organization states of functional molecules have a significant impact on the properties of materials. A variety of approaches have been studied to obtain well-organized molecular assemblies. The present work shows a new non-organized state of isolated and dispersed functional molecules in amorphous flexible covalent organic networks. Redox-active quinone molecules are embedded in the amorphous network polymers. Consecutive reactions between benzoquinone (BQ) and linker molecules generate random network structures through polymerization at different rates and in multiple directions. The low-crystalline stackings of the amorphous network polymers facilitate the formation of nanoflakes through exfoliation in dispersion media. Enhanced electrochemical performances, one of the highest specific capacities in recent studies, were achieved by efficient redox reactions of the quinone moiety. The present noncrystalline approach, low-crystalline stacking of designer amorphous covalent organic networks, can be applied to construct similar nanostructured polymer materials containing functional units. This journal is

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Efficient Syntheses of 2D Materials from Soft Layered Composites Guided by Yield Prediction Model: Potential of Experiment-Oriented Materials Informatics

Kyohei Noda Yasuhiko Igarashi Hiroaki Imai Yuya Oaki

Advanced Theory and Simulations (Advanced Theory and Simulations)  3 ( 7 ) 2000084 2020.07

Research paper (scientific journal), Joint Work, Accepted

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Exfoliation is a common route to synthesize 2D materials such as monolayered and few-layered nanosheets. However, it is not easy to control the breaking-down process. This work shows a new exfoliation strategy for generation of nanosheets from soft layered composites in high yield. Soft layered composites of inorganic hosts and organic guests are exfoliated into nanosheets in organic dispersion media. A simple yield prediction model is constructed on small-scale experimental data by sparse modeling, a data-scientific approach, combined with chemical perspective. The prediction model indicates the guest–medium combinations enabling high- and low-yield syntheses of the nanosheets. The high- and low-yield syntheses are actually achieved on different types of layered transition metal oxides in a minimum number of experiments. The number of experiments is reduced by 94%. The experimental optimization realizes further improvement of the yield, namely, shortening the exfoliation time. The present strategies can be applied to obtain a variety of 2D materials through exfoliation. Moreover, the present work suggests that combination of small experimental data, data-scientific approach, and chemical perspective, i.e., experiment-oriented materials informatics, has potentials for acceleration of materials design.

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Visualization and Quantification of Microwave using Thermo-Responsive Color-Change Hydrogel

Minami Nakamitsu, Hiroaki Imai, Yuya Oaki

ACS Sensors (ACS Sensors)  5 ( 1 ) 133 - 139 2020.06

Research paper (scientific journal), Joint Work, Accepted

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Visualization and quantification of invisible lights, such as microwaves, are significant for their safe use. In general, a sensitizer material combined with a transistor is used as electronic devices for the measurement. Here, we developed a thermoresponsive color-change hydrogel of poly(N-isopropylacrylamide) (PNIPAAm) cross-linked by a layered organic composite based on polydiacetylene (PDA) for visualization and colorimetric quantification of microwaves. The layered PDA in the PNIPAAm hydrogel showed the temperature-dependent gradual color change with heating. Irradiation of microwaves induced the color change of PDA through heating of water in the hydrogel and subsequent volume shrinkage. The color of the gel was applied to visualize the temperature distribution with increasing irradiation time of microwaves. Moreover, the power of the irradiated microwave was quantified by time to the complete color change of the gel. The results indicate that the stimulus conversion process has potentials for development of a variety of imaging and quantification devices based on the layered PDA.

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Structured spinel oxide positive electrodes of magnesium rechargeable batteries: High rate performance and high cyclability by interconnected bimodal pores and vanadium oxide coating

Kanji Ishii, Shunsuke Doi, Ryuta Ise, Toshihiko Mandai, Yuya Oaki, Shunsuke Yagi, Hiroaki Imai

Journal of Alloys and Compounds (Journal of Alloys and Compounds)  816   152556 2020.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  09258388

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A structured spinel oxide as a positive-electrode active material for magnesium rechargeable batteries was produced using a propylene-oxide-driven sol–gel method and subsequent vanadium oxide coating. Porous frameworks consisting of MgMn2O4 nanoparticles having diameters of ∼10 nm exhibited a large specific surface area of ∼150 m2 g−1 and interconnected bimodal pores distributed in the micrometer (1–10 μm) and nanometer (10–100 nm) regions. Hierarchical conduction paths constructed by mixing the porous frameworks with carbon nanoparticles reduced the overpotential for the insertion and extraction of magnesium ions and increased the redox capacity in an ionic-liquid electrolyte system. Moreover, the surface coating of vanadium oxide on the spinel oxide nanoparticles enhanced the extraction of magnesium ions and suppressed the decomposition of the electrolyte. The electrochemical properties, such as the capacities, rate capabilities, and cyclabilities, of the positive electrodes were largely improved by the structured spinel oxide frameworks.

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Biomimetic morphology–controlled anhydrous guanine via amorphous intermediate

Tsubasa Kimura, Mihiro Takasaki, Yuya Oaki, Hiroaki Imai

Crystal Growth and Design (Crystal Growth and Design)  20 ( 5 ) 3341 - 3346 2020.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  15287483

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The micrometric morphology of anhydrous β-guanine crystals is adequately designed by various organisms for their specific optical properties. We successfully controlled the morphology of an anhydrous β-guanine crystal through the transformation of an amorphous intermediate consisting of guanine sodium salt under aqueous conditions. Biomimetic platy and columnar guanine crystals were selectively produced from the amorphous intermediate by changing the crystallization conditions.

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Formation processes, size changes, and properties of nanosheets derived from exfoliation of soft layered inorganic-organic composites

Mizuguchi R., Imai H., Oaki Y.

Nanoscale Advances (Nanoscale Advances)  2 ( 3 ) 1168 - 1176 2020.03

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Exfoliation is a general route to obtain two-dimensional (2D) nanomaterials. A variety of methods have been developed for controlled exfoliation of layered materials based on stacking via van der Waals interaction, such as graphite and transition-metal dichalcogenides. On the other hand, rigid layered materials consisting of inorganic layers and interlayer metal ions stacked via electrostatic interaction, such as transition-metal oxides and clays, have a limited number of exfoliation methods. Here we studied a new exfoliation route through formation of soft layered composites. Intercalation of guest organic molecules changed rigid inorganic layered compounds into soft layered composites with stacking via van der Waals interaction. The soft layered inorganic-organic composites were exfoliated into surface-modified nanosheets in organic media. The layered composites showed swelling with dispersion in organic media. The time-course analyses suggest that the layered composites were simultaneously exfoliated in the vertical direction and fractured in the lateral direction. Thinner and smaller nanosheets were obtained with an increase in the exfoliation time. Although the resultant nanosheets gradually aggregated in the colloidal liquid, the original dispersion state was recovered with sonication for 5 min at room temperature. This exfoliation route using soft layered composites can be used in the synthesis and application of a variety of 2D nanomaterials.

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Thermally Induced Fragmentation of Nanoscale Calcite

Mihiro Takasaki, Makoto Tago, Yuya Oaki, Hiroaki Imai

RSC Advances (RSC Advances)  10 ( 10 ) 6088 - 6091 2020.02

Research paper (scientific journal), Joint Work, Accepted

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Calcite nanorods ∼50 nm wide are thermally separated into nanoblocks. The fragmentation is ascribed to the ion diffusion on metastable crystal surfaces at temperatures (∼400 °C) much lower than the melting point. The presence of water molecules enhances the surface diffusion and induces deformation of the nanorods even at ∼60 °C.

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Enhanced coercivity on self-assembled stacking of ferrimagnetic and antiferromagnetic nanocubes

Keisuke Sawano , Keishi Tsukiyama, Makoto Shimizu, Mihiro Takasaki, Yuya Oaki, Takashi Yamamoto, Yasuaki Einaga, Christian Jenewein, Helmut Cölfen, Hideo Kaiju, Tetsuya Sato, Hiroaki Imai

Nanoscale (Nanoscale)  12 ( 14 ) 7792 - 7796 2020.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  20403364

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The coercivity of magnetic nanoparticles is enhanced by the exchange coupling effect at the interface of ferrimagnetic and antiferromagnetic self-assembled monolayers. Antiferromagnetic Co3O4 nanocubes were regularly stacked on an ordered monolayer of ferrimagnetic Fe3O4 nanocubes by layer-by-layer manipulation using evaporation-driven self-assembly. The ordered arrangements of the ferrimagnetic and antiferromagnetic nanocubes are effective for the enhancement of the ferromagnetic character.

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Guanine crystals regulated by chitin-based honeycomb frameworks for tunable structural colors of sapphirinid copepod, Sapphirina nigromaculata

Tsubasa Kimura, Mihiro Takasaki, Ryosuke Hatai, Yukiko Nagai, Katsuyuki Uematsu, Yuya Oaki, Minoru Osada, Hiroyuki Tsuda, Takaaki Ishigure, Takashi Toyofuku, Shinji Shimode, Hiroaki Imai

Scientific Reports (Scientific Reports)  10 ( 1 ) 2266 2020.02

Research paper (scientific journal), Joint Work, Accepted

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Sapphirinid copepods, which are marine zooplankton, exhibit tunable structural colors originating from a layered structure of guanine crystal plates. In the present study, the coloring portion of adult male of a sapphirinid copepod, Sapphirina nigromaculata, under the dorsal body surface was characterized to clarify the regulation and actuation mechanism of the layered guanine crystals for spectral control. The coloring portions are separated into small domains 70–100 µm wide consisting of an ordered array of stacked hexagonal plates ~1.5 µm wide and ~80 nm thick. We found the presence of chitin-based honeycomb frameworks that are composed of flat compartments regulating the guanine crystal plates. The structural color is deduced to be tuned from blue to achromatic via yellow and purple by changing the interplate distance according to vital observation and optical simulation using a photonic array model. The framework structures are essential for the organization and actuation of the particular photonic arrays for the exhibition of the tunable structural color.

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Amorphous 2D Materials Containing Conjugated-Polymer Network

Shoichiro Yano, Kosuke Sato, Jumpei Suzuki, Hiroaki Imai, Yuya Oaki

Communications Chemistry (Communications Chemistry)  2 ( 1 ) 97 2019.12

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2399-3669

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Two-dimensional materials, such as layered compounds and nanosheets, have attracted interest for their characteristic structures and properties. If layered materials containing functional organic molecules are synthesized, designed nanosheets can be obtained by exfoliation. Here we show the design and synthesis of an amorphous organic layered material containing a conjugated-polymer network, its exfoliation into nanosheets, and their applications. Copolymerization of benzoquinone and pyrrole generates random stacks of the conjugated polymer layers through successive C-C bond formation and pericyclic reaction under mild conditions at 60 °C. The amorphous organic layered materials are efficiently exfoliated into nanosheets in 44.6% after 1 h. The nanosheets are used as a metal-free electrocatalyst for hydrogen evolution reaction with the overpotential 0.28 V (vs. RHE). The present approach may be applied to the design of functional nanosheets with graphene-like structures under mild conditions.

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A paper-based device of a specially designed soft layered polymer composite for measurement of weak friction force

Kei Watanabe, Hiroaki Imai, Yuya Oaki

Journal of Materials Chemistry C (Journal of Materials Chemistry C)  8 ( 4 ) 1265 - 1272 2019.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  20507534

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Measurement of friction force is important for safety, security, and health. Excessive friction force causes degradation of materials and biological bodies. For example, tooth enamel and gums are damaged by strong toothbrushing force. However, friction force is not easily measured by conventional materials and devices. Here, we proposed design strategies of a paper-based device for measurement of friction force. Toothbrushing force, a model of weak friction force, is the measurement target in the present work. Soft layered composites of polydiacetylene (PDA) and interlayer guest macromolecules were designed and synthesized to achieve a visible color change in response to weak friction force. A data-scientific approach assisted in the selection of the interlayer guest molecule to control the stimuli responsivity of the layered PDA. The guest polyethyleneimine (PEI) formed soft layered composites exhibiting a color change in response to weak friction force. The paper-based device of the layered PDA/PEI composite showed a gradual color change from blue to red in response to the strength and number of the applied friction force. As a model case, toothbrushing force was measured using the paper-based device. The present work shows new design strategies of molecules and materials toward measurement of a wide variety of friction forces.

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Experiment-Oriented Materials Informatics for Efficient Exploration of Design Strategy and New Compounds for High-Performance Organic Anode

Numazawa H., Igarashi Y., Sato K., Imai H., Oaki Y.

Advanced Theory and Simulations (Advanced Theory and Simulations)  2 ( 10 )  2019.10

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High-performance organic energy storage has attracted much interest as a future battery. Organic anode has been developed as an alternate of graphite in the past decade. However, the design strategies are not fully studied for further development. The present work shows experiment-oriented materials informatics (MI) for efficient exploration of design strategy and new compounds for an active material of high-performance organic anode. A few important factors to achieve high specific capacity are extracted from training dataset containing experimentally measured specific capacity, calculation results, and literature data of the model compounds using sparse modeling, an informatics approach. Although the prediction model is not sufficiently accurate, the model assists in exploration of new compounds in combination with experience and intuition of experimental scientists. New compounds with high specific capacity, such as 227 mA h g–1 at 100 mA g–1 for benzo[1,2-b:4,5-b′]dithiophene (BdiTp), are efficiently discovered in a minimum number of experiments. Furthermore, polymerization of BdiTp exhibits the enhanced performances, such as 933 mA h g–1 at 20 mA g–1 and cycle stability, and rate performance. MI combined with experiment, calculation, and data accelerates design new materials and functions by experimental scientists having their small data, experience, and intuition.

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Glass-transition-induced color-changing resins containing layered polydiacetylene

Shuhei Ishioka, Kei Watanabe, Hiroaki Imai, Yu-Jen Tseng, Chi-How Peng, Yuya Oaki

Chemical Communications (Chemical Communications)  55 ( 78 ) 11723 - 11726 2019.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  13597345

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A phase-segregated composite of polystyrene (PSt) and layered polydiacetylene (PDA) was formed through simultaneous polymerization and crystallization. As the motion of PSt chains with glass transition is transferred to that of PDA, the color change was achieved by the shortening of the conjugation length with deformation of the layered structure.

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Evolution of Co<inf>3</inf>O<inf>4</inf> Nanocubes through Stepwise Oriented Attachment

Tsukiyama K., Takasaki M., Oaki Y., Imai H.

Langmuir (Langmuir)  35 ( 24 ) 8025 - 8030 2019.06

ISSN  07437463

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Uniformly sized building units are generally required to construct highly elaborate architectures over a wide range. Defined nanocubes of Co3O4 evolved from deformed precursor nanograins 2-5 nm in diameter through direct oriented attachment in a nonpolar medium. Uniformly sized primary nanocubes -8 nm on a side with {100} faces were formed by adjusting the coverage of the oxide nanograins with oleic acid. Larger nanocubes 20-40 nm on a side were produced with further direct oriented attachment of the primary nanocubes. Ordered arrays, such as superlattices, were found to be constructed by the indirect oriented attachment of the primary and larger nanocubes covered with organic molecules.

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Evolution of Co3O4 Nanocubes through Stepwise Oriented Attachment

Keishi Tsukiyama, Mihiro Takasaki, Yuya Oaki, Hiroaki Imai

Langmuir 35   8025 - 8030 2019.05

Research paper (scientific journal), Joint Work, Accepted

Highly Dispersive Mono-Sized Nanoparticles of Y2O3-Stabilized ZrO2

K. Tsukiyama, M. Takasaki, Y. Oaki, H. Imai

Chemistry Letters 48   390 - 393 2019.03

Research paper (scientific journal), Joint Work, Accepted

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Quantitative detection of near-infrared (NIR) light using organic layered composites

Machi Takeuch, Hisato Kawashima, Hiroaki Imai, Syuji Fujii, Yuya Oaki

Journal of Materials Chemistry C (Journal of Materials Chemistry C)  7 ( 14 ) 4089 - 4095 2019.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  20507534

　View Summary

Quantitative detection of external stimuli, such as light, heat, and force, is an important challenge for sensing materials. Near-infrared (NIR) light is used in a variety of fields, such as biological, physical, medical, and engineering applications. Visualization and quantitative detection of invisible NIR are significant for its safe use. Here we fabricate a paper-based device coated with polypyrrole (PPy) and layered polydiacetylene (PDA). As PPy induces evolution of heat with irradiation of NIR, the effective conjugation length of the layered PDA is changed by the dynamic structure changed through the heat conduction. The visible color change from blue to red proceeds on the paper device. The red-color intensity has a relationship with the irradiation power of NIR. These facts suggest that the irradiation time and power of NIR are quantified by the color. Moreover, the results indicate that layered PDA can be applied to the quantification of external stimuli through conversion from the desired stimulus to the detectable one.

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Enhanced Oxide-Ion Conductivity of Solid-State Electrolyte Mesocrystal

K. Tsukiyama, M. Takasaki, N. Kitamura, Y. Idemoto, Y. Oaki, M. Osada, H. Imai

Nanoscale (Nanoscale)  11 ( 10 ) 4523 - 4530 2019.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  20403364

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Oxide ion-conducting porous films were produced on a substrate by evaporation-induced self-assembly of rare earth-doped CeO 2 (REDC) nanocubes 4-5 nm in size and subsequent mild calcination at 400 °C. Mesocrystalline structures comprising iso-oriented REDC nanocubes were formed by ordered assembly based on strict attachment of their {100} faces. Enhanced oxide-ion conductivities in a temperature range of 250-350 °C were observed on the mesocrystalline films consisting of Sm-doped CeO 2 (SDC) nanocubes. The specific electrical properties of the mesocrystalline films are ascribed to improved surface-ion conduction due to a large specific surface area and a high crystallographic connectivity of SDC nanocubes.

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Bending Fibers of Hydroxyapatite for Ordered Parallel Architecture in Bovine Tooth Enamel

Y. Yukimasa, M. Takasaki, Y. Oaki, H. Imai

ACS Omega (ACS Omega)  4 ( 2 ) 3739 - 3744 2019.02

Research paper (scientific journal), Joint Work, Accepted

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The nanometer-scale bending structure in the enamel-dentin interfacial region of bovine teeth was clarified using detailed electron micrographs. We found that enamel prisms of width 5-10 μm in the enamel are regarded as a bundle of nanometer-scale hydroxyapatite (HA) fibers of width 20-30 nm that are connected to the enamel-dentin interface. The radial arrangements of HA fibers elongated in the c-axis were formed on the dentin surface at the boundary. The orientation adjustment of the HA fibers was observed through stepwise bending with a gradual change of the c direction in the ordered parallel array of the enamel prisms. Our observation suggests that the crystallographic ordering in the enamel layer originates from the growth-induced orientation of HA crystals in the interfacial region.

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Redox-Mediated High-Yield Exfoliation of Layered Composites into Nanosheets

Y. Yamamoto, H. Imai, Y. Oaki

Bulletin of the Chemical Society of Japan (The Bulletin of the Chemical Society of Japan)  92 ( 4 ) 779 - 784 2019.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00092673

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A variety of organic and inorganic layered compounds are exfoliated into 2D nanomaterials in liquid phase. Improvement of exfoliation yield is a significant challenge for further applications of 2D nanomaterials. However, yield of transition-metal-oxide nanosheets is not so high, such as around 5% for 240 h and 15% for 120 h, in previous exfoliation methods. Here we show a new exfoliation approach to high-yield synthesis of nanosheets. A layered composite of cobalt hydroxide and guest quinone derivative was exfoliated into nanosheets through redox reactions of the interlayer guests in the yield 1657% for 1 h under mild conditions. The redox reactions of the guest molecules on the layer facilitate efficient exfoliation through improvement of the affinity between the guest and dispersion medium. The present redox-mediated exfoliation approach can be applied to efficient synthesis of a variety of 2D nanomaterials from layered composites.

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Materials-informatics-assisted high-yield synthesis of 2D nanomaterials through exfoliation

G. Nakada, Y. Igarashi, H. Imai, Y. Oaki

Advance Theory and Simulations (Advanced Theory and Simulations)  2 ( 4 ) 1800180 2019.01

Research paper (scientific journal), Joint Work, Accepted

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A variety of inorganic and organic nanosheets with characteristic structures and properties can be synthesized through exfoliation of layered materials. However, in general, immense time and efforts are required for exploration of exfoliation conditions and characterization of nanosheets. In addition, it is challenging to improve the yield of nanosheets obtained through exfoliation. Here a materials-informatics-assisted high-yield synthesis of nanosheets is proposed, which does not require experience and intuition. Layered composites containing inorganic layers and interlayer organic guests are delaminated into nanosheets in a variety of dispersion media. First, an experimental screening is performed to find efficient exfoliation conditions and obtain a training dataset for the informatics approach. Sparse modeling is then used facilitating the extraction of important factors predicting the yield of nanosheets. High-yield (up to ≈50%) synthesis of nanosheets is demonstrated in unknown systems in a minimum number of experiments. The yield is higher than those typically reported for layered materials. It is expected that the effective combination has potentials for not only discovery of compounds but also structure control of materials.

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Pyrolytic production of fluorescent pyrone derivatives produced in the confined space of super-microporous silicas

Kosei Hayashi, Shumpei Ogawa, Hiroto Watanabe, Yasuto Fujimaki, Yuya Oaki, Hiroaki Imai

The Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan)  92 ( 7 ) 1170 - 1174 2019.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00092673

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Fluorescent pyrone derivatives were extracted from the pyrolitic product of citric acid confined in supermicroporous silicas (SMPSs). We utilized the tiny spaces of SMPSs to produce fluorescent molecules as small fragments of carbogenic dots. We characterized their optical properties and investigated their structual information. The obtained molecule was determined as a pyrone derivative. The isolated product showed similar optical properties to those of reported carbogenic dots. Therefore, we suggest that the pyrone structure is the key fragment structure of carbogenic dots.

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Supermicroporous silica nanograins: Synthesis and application

Riku Kitamura, Hiroto Watanabe, Yuya Oaki, Hiroaki Imai

Langmuir (Langmuir)  35   5594 - 5598 2019.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  07437463

　View Summary

Supermicroporous silicas having micropores 1-2 nm in diameter were miniaturized to 30-40 nm in diameter using a combination of binary organic agents: cationic surfactant as a porogen and polyethylene glycol as a growth suppressor in a concentrated system. The miniaturized nanograins of the porous silica were effective as a porous and transparent matrix for WO 3 quantum dots that exhibit enhanced photocatalytic activity.

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Enhanced quantum yield of nanographenes incorporated in supermicroporous silicas and the co-adsorption effect of water molecule

H. Watanabe, Y. Fujimaki, K. Hayashi, H. Imai

The Bulletin of the Chemical Society of Japan  2019

Research paper (scientific journal), Joint Work, Accepted

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Highly dispersive mono-sized nanoparticles of Y <inf>2</inf> O <inf>3</inf> -stabilized ZrO <inf>2</inf>

Tsukiyama K., Takasaki M., Oaki Y., Imai H.

Chemistry Letters (Chemistry Letters)  48 ( 4 ) 390 - 393 2019

ISSN  03667022

　View Summary

Uniformly sized nanoparticles 35nm in diameter of Y 2 O 3 - stabilized ZrO 2 (YSZ) were fabricated by a water-toluene twophase solvothermal method. The nanoparticles that were covered with oleic acid were highly dispersed in organic media. The size and doping concentration were tuned by adjusting the preparation conditions. The fabrication of YSZ thin films was achieved through hexagonal arrangement by evaporation-induced selfassembly of highly dispersive mono-sized nanoparticles.

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Biomimetic Macroscopic Mesocrystalline Films Produced by Oriented Assembly of Nanorods under Magnetic Field

M. Takasaki, T. S. Suzuki, Y. Oaki, H. Imai

Nanoscale (Nanoscale)  10 ( 47 ) 22161 - 22165 2018.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  20403364

　View Summary

Millimeter-scale mesocrystals and cross-lamellae mimicking the nanostructure of seashells were produced on a substrate through the three-dimensionally oriented assembly of c-axis-elongated calcite nanorods ∼50 nm wide and ∼500-1000 nm long by combining arrangement with evaporation-driven capillary force and alignment under an intense magnetic field.

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Tunable Stimuli-Responsive Color-Change Properties of Layered Organic Composite

M. Takeuchi, K. Gnanasekaran, H. Friedrich, H. Imai, N. A. J. M. Sommerdijk, Y. Oaki

Advanced Functional Materials (Advanced Functional Materials)  28 ( 45 ) 1804906 2018.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1616301X

　View Summary

Stimuli-responsive properties of soft materials originate from dynamic structure changes. Layered polydiacetylene (PDA) shows color-change properties with the application of external stimuli, such as thermal and mechanical stresses. Layered organic materials possessing intercalation capabilities and dynamic properties have potentials for tuning their structures and properties by the intercalated guests. A variety of sensing and imaging devices can be developed by control of the stimuli responsivity. Here, the key structures, processes, and mechanisms for tuning the stimuli-responsive color-change properties of layered PDA are studied by in situ analyses with heating and cooling. The in situ analyses indicate that heating initiates thermal motion of the alkyl side chains of the PDA main chain in the host layers around 60 °C, regardless of the type of intercalated guests. Further heating induces torsion of the PDA main chain leading to color changes at different temperatures, depending on the types of the intercalated guest. Then, the layered structure is irreversibly deformed with lowering the crystallinity. The results indicate that the stimuli-responsive color-change properties are controlled by the rigidity of the layered structures consisting of the host layers and guests. The control strategy based on rigidity tuning can be applied to a variety of soft materials with stimuli responsivity.

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Enhanced detection of methylmercaptan gas using proton containing layered manganese oxide nanosheets coated on quartz crystal microbalance

Kawamura, N; Tokura, Y; Nakada, G; Oaki, Y; Imai, H; Shiratori, S

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 256 2018.08

ISSN  0065-7727

Manganese oxide nanosheets on quartz crystal microbalance for detection of methylmercaptan gas

Tokura, Y; Nakada, G; Oaki, Y; Imai, H; Shiratori, S

ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 256 2018.08

ISSN  0065-7727

Highly Porous Polymer Dendrites of Pyrrole Derivatives Synthesized through Rapid Oxidative Polymerization

K. Ishii, K. Sato, Y. Oaki, H. Imai

Polymer Journal (Polymer Journal)  51 ( 1 ) 11 - 18 2018.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00323896

　View Summary

Highly porous organic structures are synthesized by the oxidative polymerization of pyrrole derivatives in a concentrated monomer and oxidant solution. The rapid polymerization of pyrrole by oxidation with FeCl3 in CHCl3 as a cosolvent for the monomer and the oxidant leads to nanometer-scale branching morphologies that have a specific surface area of ~200 m2 g−1. The polymerization of pyrrole derivatives, such as 1-methylpyrrole and 1-ethylpyrrole, produced intragranular micropores of ~1 nm in diameter in the polymer grains of nanoscale dendrites. We obtained highly porous polymers of polypyrrole derivatives that have high specific surface areas (~900 m2 g−1) with bimodal pore-size distribution. The enhanced adsorbability of porous polymer dendrites for aromatic molecules was confirmed, in comparison with that of conventional polystyrene adsorbents.

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Layer-by-Layer Manipulation of Heterogeneous Rectangular Nanoblocks: Brick Work for Multilayered Structures with Specific Heterojunction

R. Matsumoto, M. Takasaki, K. Tsukiyama, Y. Oaki, H. Imai

Inorganic Chemistry (Inorganic Chemistry)  57 ( 18 ) 11655 - 11661 2018.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00201669

　View Summary

The combination of heterogeneous inorganic nanocrystals provides novel nanometer-scale architectures for exploration of novel functions. In the present study, heterogeneous bilayers, such as BaTiO3-Fe3O4 and Mn3O4-CeO2, are fabricated via layer-by-layer stacking of several rectangular nanoblocks 5-23 nm in size by evaporation-driven self-assembly. Specific heterojunctions between inorganic crystals are constructed by nanoscale simple brick work through spontaneous adjustment of the crystallographic orientations of the nanoblocks in the lower and upper layers.

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Two-dimensional Conductive and Redox-Active Nanostructures Synthesized by Crystal-Controlled Polymerization for Electrochemical Applications

K. Sato, H. Imai, Y. Oaki

ACS Applied Nano Materials (ACS Applied Nano Materials)  1 ( 8 ) 4218 - 4226 2018.07

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Two-dimensional nanomaterials have attracted much interest for their anisotropic structures and emergent properties. Whereas a variety of inorganic nanosheets are prepared by exfoliation, design and synthetic strategies of organic nanosheets are still developing. Here we report on crystal-controlled synthesis of conductive and redox-active organic polymer nanosheets with tunable thickness and lateral size. Although the nanosheets consist of classical conductive polymers, such as polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT), a new crystal-controlled polymerization approach provides 2D nanomaterials with enhanced and characteristic properties. Oxidative polymerization proceeds on the crystal surface of organic oxidants, such as quinone derivatives, with diffusion of the monomer vapor at low temperature under ambient pressure. The present method affords the control of lateral size and thickness of the nanosheets. The resultant nanosheets show the characteristic and enhanced properties originating from a 2D nature, such as the high structure anisotropy with aspect ratio around 104, enhanced conductivity 287 S cm-1, and specific charge-discharge capacitance 523 F g-1 at the current density of 18 A g-1. The organic nanosheets with conductivity and redox activity can be used as a building block for development of functional materials and devices. ©

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Multistage redox reactions of conductive-polymer nanostructures with lithium ions: potential for high-performance organic anodes

Numazawa H., Sato K., Imai H., Oaki Y.

NPG Asia Materials (NPG Asia Materials)  10 ( 5 ) 397 - 405 2018.05

ISSN  18844049

　View Summary

Conducive polymers have a wide range of applications originating from their π-conjugated systems. The redox reactions of conductive polymers with doping and dedoping of anions have been applied to cathodes for charge storage. In contrast, the redox reactions with cations have not been fully studied in anodes for charge storage. Here, we found that the nanostructures of conductive polymers, such as polypyrrole (PPy) and polythiophene (PTp) derivatives, have reversible redox reactions with cations. The PPy and PTp nanostructures acted as anodes with specific capacities of 157 and 44.4 mA h g–1, respectively, at a current density of 20 mA g–1. The introduction of a carboxy group to the pyrrole and thiophene rings enhanced the specific capacities up to 730 and 963 mAh g–1, respectively. The enhanced electrochemical properties were not observed in the bulk-size conductive polymers. The results suggest that conductive-polymer nanostructures have potential for developing metal-free, high-performance charge storage devices.

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Layer-by-Layer Manipulation of Anisotropic Nanoblocks: Orientation-Switched Superlattices through Orthogonal Stacking of a and c Directions

Y. Nakagawa, R. Matsumoto, H. Kageyama, Y. Oaki, H. Imai

Nanoscale (Nanoscale)  10 ( 27 ) 12957 - 12962 2018.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  20403364

　View Summary

Nanometer-scale switching of the crystallographic orientation enables production of novel superlattices for exploration of new functions. Elaborate multilayered architectures of Mn3O4 nanocuboids were constructed by a convective self-assembly process. The nanometric cuboids were accumulated into orientation-switched superlattices on micrometric scales by controlling the a and c directions of the tetragonal crystal periodically. The orthogonal stacking of the tetragonal nanoblocks was achieved through the layer-by-layer manipulation process of two types of 2D arrays with different orientations.

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Nanoscale Mosaic Works: Tetragonal Lattices of Iso-Oriented Heterogeneous Nanocubes

R. Matsumoto, H. Yamazaki, M. Takasaki,Y. Oaki, T. Sato, H. Imai

Langmuir (Langmuir)  34 ( 13 ) 4031 - 4035 2018.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  07437463

　View Summary

Tetragonal 2D lattices are spontaneously formed by the self-assembly of homogeneous nanocubes. However, ordered arrays consisting of differently sized rectangular nanoblocks have not been achieved because the regulation of the assembly is weakened by the combination of binary units. In the present work, ordered arrays comprising binary nanocubes were investigated using the combination of 10 nm Pt nanocubes and 20 nm BaTiO3 nanocubes. Heterogeneous but ordered 2D tetragonal lattices were successfully produced using differently sized rectangular nanoblocks. The highly ordered self-assembly in the heterogeneous system requires the matching of the size ratio of binary nanocubes with the buffer effect of oleic acid covering the building units.

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Enhanced electrochemical properties of MgCo<inf>2</inf>O<inf>4</inf> mesocrystals as a positive electrode active material for Mg batteries

Kotani Y., Ise R., Ishii K., Mandai T., Oaki Y., Yagi S., Imai H.

Journal of Alloys and Compounds (Journal of Alloys and Compounds)  739   793 - 798 2018.03

ISSN  09258388

　View Summary

Mesocrystals of MgCo2O4 spinel oxide exhibiting porous and single-crystalline structures were synthesized by the reaction of magnesium ions with calcite-type CoCO3 mesocrystal precursors grown in micrometer-sized agar gels. The mesocrystals consisted of single-crystalline porous grains measuring 200–300 nm in diameter with iso-oriented subunits of approximately 10 nm. The single-crystalline porous framework structure of the MgCo2O4 mesocrystals enhanced the discharge capacity and positively shifted the discharge potential compared with MgCo2O4 nanoparticles prepared by the inverse co-precipitation method. These enhancements were attributed to a combination of the high specific surface areas of the mesocrystals and the high connectivity of the magnesium ion diffusion paths in the solid-phase.

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Enhanced Electrochemical Properties of MgCo2O4 Mesocrystals as a Positive Electrode Active Material for Mg Batteries

Y. Kotani, R. Ise, K. Ishii, T. Mandai, Y. Oaki, S. Yagi, H. Imai

Journal of Alloys and Compounds 739   793 - 798 2018.03

Research paper (scientific journal), Joint Work, Accepted

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Artificial Mineral Films Similar to Biogenic Calcareous Shells: Oriented Calcite Nanorods on a Self-Standing Polymer Sheet

Y. Nagai, Y. Oaki, H. Imai

CrystEngComm (CrystEngComm)  20 ( 12 ) 1656 - 1661 2018.01

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Micrometre-thick calcareous shells consisting of c-axis-oriented calcite nanorods are produced on an organic sheet as foraminiferal tests and isopod cornea cuticles. Here, we produced mineral films similar to biogenic calcareous shells on a self-standing polymer sheet in a supersaturated solution system by multistep crystal growth with the adjustment of the concentration ratio of poly(acrylic acid) (PAA) as a soluble controlling agent. In the initial stage, selective high-density nucleation was achieved at a relatively low PAA to calcium ion ratio (R = 1.0-1.2) to form of a calcite seed layer on the surface of conventional polyvinyl alcohol. Calcite nanorods elongated in the c direction were then grown perpendicularly to the seed layer in the progressive stages at a relatively high PAA ratio (R = 1.5-2.0). The artificial mineral films consisting of c-axis-oriented nanorods are suggested to exhibit mechanical properties similar to those of biogenic calcareous shells.

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Crystal-controlled polymerization: recent advances in morphology design and control of organic polymer materials

Oaki Y., Sato K.

Journal of Materials Chemistry A (Journal of Materials Chemistry A)  6 ( 46 ) 23197 - 23219 2018

ISSN  20507488

　View Summary

Morphologies are important in chemistry and materials science. A wide variety of functional molecules and their assemblies are synthesized on the basis of molecular design. These morphologies, from molecular to nanometer scales, have been summarized in previous nice reviews. Here we focus on recent advances in morphology design and control of organic polymer materials from nanoscopic to macroscopic scales, which are larger than the molecular scale, for which general strategies are now being developed. This review summarizes crystal-controlled polymerization from a new perspective for the morphology design and control of organic polymer materials. Characteristic structures, surfaces, and morphologies of solid crystals are employed for morphology control of organic polymer materials. Morphology control contributes to the emergence and/or improvement of the properties.

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Evolution of Calcite Nanocrystals through Oriented Attachment and Fragmentation: Multi-Step Pathway Involving Bottom-Up and Break-Down Stages

M. Takasaki, Y. Kezuka, M. Tajika, Y. Oaki, H. Imai

ACS Omega 2 ( 12 ) 8997 - 9001 2017.12

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2470-1343

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Spatial Control of Crystallographic Direction in 2D Microarrays of Anisotropic Nanoblocks on Trenched Substrates

R. Matsumoto, Y. Nakagawa, K. Kato, Y. Oaki, H. Imai

Langmuir 33 ( 48 ) 13805 - 13810 2017.12

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0743-7463

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Hierarchical Textures on Aragonitic Shells of a Hyaline Radial Foraminifer Hoeglundina elegans

K. Nakajima, M. Suzuki, Y. Nagai, K. Izumida, Y. Oaki, T. Toyofuku, J. Bijma, G. Nehrke, M. Raitzsch, K. Tani, H. Imai

CrystEngComm 19 ( 47 ) 7191 - 7196 2017.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1466-8033

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Enhanced quantum yield of fluorophores in confined spaces of supermicroporous silicas

S. Ogawa, T. Wakayama, H. Watanabe, K. Hayashi, S. Ogata, Y. Oaki, M. Hasegawa, H. Imai

The Bulletin of the Chemical Society of Japan (Bulletin of the Chemical Society of Japan)  91 ( 1 ) 87 - 91 2017.10

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00092673

　View Summary

The optical properties of polycyclic aromatic hydrocarbon fluorophores, such as pyrene and perylene, are controlled by confined spaces of meso- and supermicropores in a silica matrix. The quantum yield of fluorescence from monodispersed pyrene and perylene increases with limitation of the excimer formation in 1 nm supermicropores. When the pore diameter is close to the molecular size, solid-state fluorescence having a high quantum yield is achieved via the fluorophores in the confined spaces by suppressing the aggregation, the interaction with charge-transfer sites and the stabilization of the excited state.

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Polymer-Assisted Shapeable Synthesis of Porous Frameworks Consisting of Silica Nanoparticles with Mechanical Property Tuning

K. Sato, K. Ishii, Y. Oaki, K. Nakanishi, H. Imai

Polymer Journal 49 ( 12 ) 825 - 830 2017.10

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0032-3896

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Ultrasensitive Detection of Methylmercaptan Gas Using Layered Manganese Oxide Nanosheets with a Quartz Crystal Microbalance Sensor

Y. Tokura, G. Nakada, Y. Moriyama, Y. Oaki, H. Imai, S. Shiratori

Analytical Chemistry 89 ( 22 ) 12123 - 12130 2017.10

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0003-2700

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Evolution analysis of V2O5·nH2O gels for preparation of xerogels having a high specific surface area and their replicas

K. Ishii, Y. Kimura, T. Yamazaki, Y. Oaki, H. Imai

RSC Advances 7   35711 - 35716 2017.07

Research paper (scientific journal), Joint Work, Accepted

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Substrate coating by conductive polymers through spontaneous oxidation and polymerization

Kuwabara Kento, Masaki Hirotaka, Imai Hiroaki, Oaki Yuya

NANOSCALE 9 ( 23 ) 7895 - 7900 2017.06

ISSN  2040-3364

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Self-organized Formation of Parallel-banded Structures through Synchronization of Twisted Growth

S. Mizue, S. Ibaraki, R. Ise, G. Sazaki, Y. Oaki, H. Imai

Crystal Growth and Design 17 ( 7 ) 3694 - 3699 2017.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1528-7483

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Synthesis of poly(amidoamine) dendrimer having a 1,10-bis(decyloxy)decane core and its use in fabrication of carbon nanotubes/calcium carbonate hybrids through biomimetic mineralization

S. Nishimura, T. Tajima, T. Hasegawa, T. Tanaka, Y. Takaguchi, Y. Oaki, H. Imai

Canadian Journal of Chemistry 2017 ( 9 ) 935 - 941 2017.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0008-4042

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Synthesis of dispersible nanosheets based on monolayer clays with imidazolium and ammonium ations aving long-chain alkyl groups

A. Suzuki, Y. Oaki, H. Imai

Journal of the Ceramics Society of Japan 125 ( 4 ) 353 - 356 2017.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1882-0743

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Significant increase in bandgap and emission efficiency of In2O3 quantum dots by size-tuning around 1 nm in supermicroporous silicas

T. Suzuki, H. Watanabe, T. Ueno, Y. Oaki, H. Imai

Langmuir 33 ( 12 ) 3014 - 3017 2017.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0743-7463

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Oriented Attachment of Calcite Nanocrystals: Formation of Single-Crystalline Configurations as 3D Bundles via Lateral Stacking of 1D Chains

M. Takasaki, Y. Oaki, H. Imai

Langmuir 33 ( 6 ) 1516 - 1520 2017.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0743-7463

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Effects of Nanostructured Biosilica in Rice Plant Mechanics, RSC Advances

K. Sato, N. Ozaki, K. Nakanishi, Y. Sugahara, Y. Oaki, C. Salinas, S. Herrera, D. Kisailus, H. Imai

RSC Advances 7 ( 22 ) 13065 - 13071 2017.02

Research paper (scientific journal), Joint Work, Accepted

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Stepwise Rotation of Nanometric Building Blocks in Aragonite Helix of a Pteropod Shell

M. Suzuki, T. Sasaki, Y. Oaki, H. Imai

Crystal Growth and Design 17 ( 1 ) 191 - 196 2017.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1528-7483

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Multistep Crystal Growth of Oriented Fluorapatite Nanorod Arrays for Fabrication of Enamel-Like Architectures on a Polymer Sheet

K. Nakamura, Y. Oaki, H. Imai

CrystEngComm 19 ( 4 ) 669 - 674 2017.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1466-8033

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Crystal-Induced Nanoarchitectonics of Organic Polymer Materials

Oaki Y.

SUPRA-MATERIALS NANOARCHITECTONICS    221 - 246 2017

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Bio-inspired synthesis of xLi₂MnO₃-(1-x) LiNi_0.33Co_0.33Mn_0.33O₂ lithium-rich layered cathode materials

Hou, CX; Oaki, Y; Hosono, E; Lin, H; Imai, H; Fan, YQ; Dang, F

MATERIALS & DESIGN 109   718 - 725 2016.11

ISSN  0264-1275

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Orientation-Selective Alignments of Hydroxyapatite Nanoblocks through Epitaxial Attachment in <i>a</i> and <i>c</i> Directions

Nakamura, K; Nakagawa, Y; Kageyama, H; Oaki, Y; Imai, H

LANGMUIR 32 ( 16 ) 4066 - 4070 2016.04

ISSN  0743-7463

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UV-induced Epitaxial Attachment of TiO2 Nanocrystals in Molecularly Mediated 1D and 2D Alignments

T. Hiraide, H. Kageyama, Y. Nakagawa, Y. Oaki, H. Imai

Chemical Communications 52   7545 - 7548 2016

Research paper (scientific journal), Joint Work, Accepted

Selectively Assembled 2D Microarrays from Binary Nanocrystals

C. Hou, T. Liua, Y. Fan, H. Imai, R. Fan, H. Lin, Q. He, N. Wang, F. Dang, Z. Guo

CrystEngComm 18   3008 - 3014 2016

Research paper (scientific journal), Joint Work, Accepted

Orientation-Selective Alignments of Nanoblocks in a and c Directions of Tetragonal System through Molecularly Mediated Manipulation

Y. Nakagawa, H. Kageyama, Y. Oaki, H. Imai

Chemical Communications 52   5597 - 5600 2016

Research paper (scientific journal), Joint Work, Accepted

Orientation-Selective Alignments of Hydroxyapatite Nanoblocks through Epitaxial Attachment in a and c Directions

K. Nakamura, Y. Nakagawa, H. Kageyama, Y. Oaki, H. Imai

Langmuir 32   4066 - 4070 2016

Research paper (scientific journal), Joint Work, Accepted

Tuning of photocatalytic reduction by conduction band engineering of semiconductor quantum dots with experimental evaluation of band edge potential

T. Suzuki, H. Watanabe, Y. Oaki, H. Imai

Chemical Communications 52   6185 - 6188 2016

Research paper (scientific journal), Joint Work, Accepted

Optical Properties of Biosilicas in Rice Plants

K. Sato, A. Yamauchi, N. Ozaki, T. Ishigure, Y. Oaki, H. Imai

RSC Advances 6 ( 110 ) 109168 - 109173 2016

Research paper (scientific journal), Joint Work, Accepted

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Switchable Oriented Attachment and Detachment of Calcite Nanocrystal

M. Takasaki, Y. Oaki, H. Imai

CrystEngComm 18   8999 - 9002 2016

Research paper (scientific journal), Joint Work, Accepted

Bio-inspired synthesis of xLi2MnO3-(1−x) LiNi0.33Co0.33Mn0.33O2 lithium-rich layered cathode materials

C. Hou, Y. Oaki, E. Hosono, H. Lin, H. Imai, Y. Fan, F. Dang

Materials and Design 109   718 - 725 2016

Research paper (scientific journal), Joint Work, Accepted

Mesoscopic Crystallographic Textures on Shells of a Hyaline Radial Foraminifer Ammonia beccarii

K. Nakajima, Y. Nagai, M. Suzuki, Y. Oaki, K. Naito, Y. Tanaka, T. Toyofuku, H. Imai

CrystEngComm 18   7135 - 7139 2016

Research paper (scientific journal), Joint Work, Accepted

Evaporation-Driven Regularization of Crystallographically Ordered Arrangements of Truncated Nanoblocks: From 1D Chains to 2D Rhombic Superlattices

R. Matsumoto, Y. Nakagawa, H. Kageyama, Y. Oaki, H. Imai

CrystEngComm 18 ( 33 ) 6138 - 6142 2016

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1466-8033

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Dendritic Growth of NaCl Crystals in a Gel Matrix: Variation of Branching and Control of Bending

M. Goto, Y. Oaki, H. Imai

Crystal Growth and Design 16 ( 8 ) 4278 - 4284 2016

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1528-7483

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1D Oriented Attachment of Calcite Nanocrystals: Formation of Single-Crystalline Rods through Collision

M. Takasaki, Y. Kimura, Y. Yamazaki, Y. Oaki, H. Imai

RSC Advances 6 ( 66 ) 61346 - 61350 2016

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2046-2069

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Aragonite Nanorod Arrays through Molecular Controlled Growth on Single-Crystalline Substrate and Polysaccharide Surface

M. Suzuki, Y. Oaki, H. Imai

Crystal Growth and Design 16 ( 7 ) 3741 - 3747 2016

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1528-7483

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UV-induced epitaxial attachment of TiO₂ nanocrystals in molecularly mediated 1D and 2D alignments

Hiraide, T; Kageyama, H; Nakagawa, Y; Oaki, Y; Imai, H

CHEMICAL COMMUNICATIONS 52 ( 48 ) 7545 - 7548 2016

ISSN  1359-7345

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Tuning of photocatalytic reduction by conduction band engineering of semiconductor quantum dots with experimental evaluation of the band edge potential

Suzuki, T; Watanabe, H; Oaki, Y; Imai, H

CHEMICAL COMMUNICATIONS 52 ( 36 ) 6185 - 6188 2016

ISSN  1359-7345

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Surface-functionalized hydrophilic monolayer of titanate and its application for dopamine detection

Matsui Hiroshi, Oaki Yuya, Imai Hiroaki

CHEMICAL COMMUNICATIONS 52 ( 60 ) 9466 - 9469 2016

ISSN  1359-7345

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Switchable oriented attachment and detachment of calcite nanocrystals

Takasaki, M; Oaki, Y; Imai, H

CRYSTENGCOMM 18 ( 47 ) 8999 - 9002 2016

ISSN  1466-8033

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Mesoscopic crystallographic textures on shells of a hyaline radial foraminifer <i>Ammonia beccarii</i>

Nakajima, K; Nagai, Y; Suzuki, M; Oaki, Y; Naito, K; Tanaka, Y; Toyofuku, T; Imai, H

CRYSTENGCOMM 18 ( 37 ) 7135 - 7139 2016

ISSN  1466-8033

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Orientation-selective alignments of nanoblocks in a and <i>c</i> directions of a tetragonal system through molecularly mediated manipulation

Nakagawa, Y; Kageyama, H; Oaki, Y; Imai, H

CHEMICAL COMMUNICATIONS 52 ( 32 ) 5597 - 5600 2016

ISSN  1359-7345

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VOC decomposition over a wide range of temperatures using thermally stable Cr<SUP>6+</SUP> sites in a porous silica matrix

Somekawa, S; Watanabe, H; Oaki, Y; Imai, H

CATALYSIS COMMUNICATIONS 72   161 - 164 2015.12

ISSN  1566-7367

• Access to Document (DOI)

Inverse pH-response of Temperature-sensitive Copolymers by Combination with Porous CaCO₃ Framework

Tamagawa, H; Kageyama, H; Oaki, Y; Hoshino, Y; Miura, Y; Imai, H

CHEMISTRY LETTERS 44 ( 10 ) 1425 - 1427 2015.10

ISSN  0366-7022

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Formation of Monocrystalline 1D and 2D Architectures via Epitaxial Attachment: Bottom-Up Routes through Surfactant-Mediated Arrays of Oriented Nanocrystals

Nakagawa, Y; Kageyama, H; Oaki, Y; Imai, H

LANGMUIR 31 ( 22 ) 6197 - 6201 2015.06

ISSN  0743-7463

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Advanced Biominnetic Approach for Crystal Growth in Nonaqueous Media: Morphology and Orientation Control of Pentacosadiynoic Add and Applications

Okaniwa Mamoru, Oaki Yuya, Kaneko Soichiro, Ishida Kazuki, Maki Hideyuki, Imai Hiroaki

CHEMISTRY OF MATERIALS 27 ( 7 ) 2627 - 2632 2015.04

ISSN  0897-4756

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Hierarchical CaCO₃ Chromatography: A Stationary Phase Based on Biominerals

Sato, K; Oaki, Y; Takahashi, D; Toshima, K; Imai, H

CHEMISTRY-A EUROPEAN JOURNAL 21 ( 13 ) 5034 - 5040 2015.03

ISSN  0947-6539

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Microwave-assisted rapid synthesis of anatase TiO₂ nanosized particles in an ionic liquid-water system

Suzuki, A; Yamaguchi, H; Kageyama, H; Oaki, Y; Imai, H

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 123 ( 1434 ) 79 - 82 2015.02

ISSN  1882-0743

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Hierarchical CaCO3 Chromatography: A Stationary Phase Based on Biominerals

Kosuke Sato, *Yuya Oaki, Daisuke Takahashi, Kazunobu Toshima, *Hiroaki Imai

Chem. Eur. J. 21   5034 - 5040 2015

Research paper (scientific journal), Joint Work, Accepted

Polymer-mediated dendritic growth of a transition metal salt crystal as a template for morphogenesis

Y. Oaki, R. Muramatsu, H. Imai

Polymer Journal 47 ( 2 ) 183 - 189 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0032-3896

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Microwave-assisted rapid synthesis of anatase TiO2 nanosized particles in an ionic liquid-water system

A. Suzuki, H. Yamaguchi, H. Kageyama, Y. Oaki, H. Imai

Journal of the Ceramic Society of Japan 123   79 - 82 2015

Research paper (scientific journal), Joint Work, Accepted

Switchable Dispersivity and Molecular-Trapping Performance of Mesostructured CaCO3/Thermosensitive Polymer Composite Microspheres

A. Inoue, H. Tamagawa, S.Aoshima, Y. Oaki, H. Imai

Journal of Materials Chemistry B 3   3604 - 3608 2015

Research paper (scientific journal), Joint Work, Accepted

Oscillatory Growth for Twisting Crystal

S. Ibaraki, R. Ise, K. Ishimori, Y. Oaki, G. Sazaki, E. Yokoyama, K. Tsukamoto, H. Imai

Chemical Communications 51   8516 - 8519 2015

Research paper (scientific journal), Joint Work, Accepted

Dynamic Adsorption of Toluene on Pore-Size Tuned Supermicroporous Silicas

H. Watanabe, K. Fujikata, Y. Oaki, H. Imai

Microporous & Mesoporous Materials 214   41 - 44 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1387-1811

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Formation of Monocrystalline 1D and 2D Architectures via Epitaxial Attachment: Bottom-Up Routes through Surfactant-Mediated Arrays of Oriented Nanocrystal

Y. Nakagawa, H. Kageyama, Y. Oaki, H. Imai

Langmuir 31   6197 - 6201 2015

Research paper (scientific journal), Joint Work, Accepted

Controlled Radical Polymerization of Styrene with Magnetic Iron Oxides Prepared through Hydrothermal, Bioinspired, and Bacterial Processes

A. Kanazawa, K. Satoh, S. Kanaoka, M. Kakihana, M. Kobayashi, J. Sato, H. Imai, Y. Oaki, A. Arakaki, K. Katagiri, M. Kamigaito, S. Aoshima

RSC Advances 5 ( 63 ) 51122 - 51129 2015

Research paper (scientific journal), Joint Work, Accepted

• Access to Document (DOI)

Fabrication of nanocellulose/hydroxyapatite composites and their application as water-resistant transparent coatings

M. Ishikawa, Y. Oaki, Y. Tanaka, H. Kakisawa, G. Salazar-Alvarez, H. Imai

Journal of Materials Chemistry B 3 ( 28 ) 5858 - 5863 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  2050-750X

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Fabrication of Self-Standing Films Consisting of Enamel-Like Oriented Nanorods Using Artificial Peptide

K. Aita, Y. Oaki, C. Ohtsuki, H. Imai

CrystEngComm 17 ( 29 ) 5551 - 5555 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1466-8033

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Fabrication of Transparent ZnO Thick Film with Unusual Orientation by the Chemical Bath Deposition

T. Morita, S. Ueno, T. Tokunaga, E. Hosono, Y. Oaki, H. Imai, H. Matsuda, H. Zhou, M. Hagiwara, S. Fujihara

Crystal Growth and Design 15 ( 7 ) 3150 - 3156 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1528-7483

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Morphology and Orientation Control of Organic Crystals in Organic Media through Advanced Biomimetic Approach

M. Okaniwa, H. Kageyama, Y. Oaki, H. Imai

Bulletin of the Chemical Society of Japan 88 ( 10 ) 1459 - 1465 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0009-2673

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Variation in Mesoscopic Textures of Biogenic and Biomimetic Calcite Crystals

R. Miyajima, Y. Oaki, T. Kogure, H. Imai

Crystal Growth and Design 15 ( 8 ) 3755 - 3761 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1528-7483

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Application of Biogenic Iron Phosphate for Lithium-Ion Battery

H. Kageyama, Y. Hashimoto, S. Saito, Y. Konishi, Y. Oaki, H. Imai

RSC Advances 5   68751 - 68757 2015

Research paper (scientific journal), Joint Work, Accepted

Inverse pH-Response of Temperature-Sensitive Copolymers by Combination with Porous CaCO3 Framework

H. Tamagawa, H. Kageyama, Y. Oaki, Y. Hoshino, Y. Miura, H. Imai

Chemistry Letters 44   1425 - 1427 2015

Research paper (scientific journal), Joint Work, Accepted

Formation of Uniformly Sized Metal Oxide Nanocuboids in the Presence of Precursor Grains in an Apolar Medium

Y. Nakagawa, H. Kageyama, R. Matsumoto, Y. Oaki, H. Imai

CrystEngComm 17 ( 39 ) 7477 - 7481 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1466-8033

• Access to Document (DOI)

VOC decomposition over a wide range of temperatures using thermally stable Cr6+ sites in a porous silica matrix

S. Somekawa, H. Watanabe, Y. Oaki, H. Imai

Catalysis Communications 72   161 - 164 2015

Research paper (scientific journal), Joint Work, Accepted

Six-Armed Twin Crystals Composed of Lithium Iron Silicate Nanoplates and Their Electrochemical Properties

H. Kageyama, Y. Hashimoto, Y. Oaki, H. Imai

CrystEngComm 17 ( 44 ) 8486 - 8491 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1466-8033

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Conductive polymer-mediated 2D and 3D arrays of Mn3O4 nanoblocks and mesoporous conductive polymers as their replicas

Y. Nakagawa, H. Kageyama, R. Matsumoto, Y. Oaki, H. Imai

Nanoscale 7   18471 - 18476 2015

Research paper (scientific journal), Joint Work, Accepted

Surface-functionalized monolayered nanodots of a transition metal oxide and their properties

M. Honda, Y. Oaki, H. Imai

Physical Chemistry Chemical Physics 17 ( 48 ) 32498 - 32504 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1463-9076

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Plant Opal-Mimetic Bunching Silica Nanoparticles Mediated by Long-Chain Polyethyleneimine

T. Hoshino, K. Sato, Y. Oaki, A. Sugawara-Narutaki, K. Shimizu, N. Ozaki, H. Imai

RSC Advances 6 ( 2 ) 1301 - 1306 2015

Research paper (scientific journal), Joint Work, Accepted

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Incorporation of Redox-Active Guest in Conductive and Redox-Active Host: Hierarchically Structured Composite of a Conductive Polymer and Quinone Derivative

K. Sato, Y. Oaki, H. Imai

Chemistry Letters 45 ( 3 ) 324 - 326 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0366-7022

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Incorporation of organic crystals into the interspace of oriented nanocrystals: morphologies and properties

Munekawa Yurika, Oaki Yuya, Sato Kosuke, Imai Hiroaki

NANOSCALE 7 ( 8 ) 3466 - 3473 2015

ISSN  2040-3364

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Application of biogenic iron phosphate for lithiumion batteries

Kageyama, H; Hashimoto, Y; Oaki, Y; Saito, S; Konishi, Y; Imai, H

RSC ADVANCES 5 ( 84 ) 68751 - 68757 2015

ISSN  2046-2069

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Switchable dispersivity and molecular-trapping performance of mesostructured CaCO₃-thermosensitive polymer composite microspheres

Inoue, A; Tamagawa, H; Oaki, Y; Aoshima, S; Imai, H

JOURNAL OF MATERIALS CHEMISTRY B 3 ( 17 ) 3604 - 3608 2015

ISSN  2050-750X

• Access to Document (DOI)

Oscillatory growth for twisting crystals

Ibaraki, S; Ise, R; Ishimori, K; Oaki, Y; Sazaki, G; Yokoyama, E; Tsukamoto, K; Imai, H

CHEMICAL COMMUNICATIONS 51 ( 40 ) 8516 - 8519 2015

ISSN  1359-7345

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Conductive polymer-mediated 2D and 3D arrays of Mn₃O₄ nanoblocks and mesoporous conductive polymers as their replicas

Nakagawa, Y; Kageyama, H; Matsumoto, R; Oaki, Y; Imai, H

NANOSCALE 7 ( 44 ) 18471 - 18476 2015

ISSN  2040-3364

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Size-Dependent Thermochromism through Enhanced Electron-Phonon Coupling in 1 nm Quantum Dots

Tamaki, H; Watanabe, H; Kamiyama, S; Oaki, Y; Imai, H

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 53 ( 40 ) 10706 - 10709 2014.09

ISSN  1433-7851

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Hydrophobic Inorganic-Organic Composite Nanosheets Based on Monolayers of Transition Metal Oxides

Honda Masashi, Oaki Yuya, Imai Hiroaki

CHEMISTRY OF MATERIALS 26 ( 11 ) 3579 - 3585 2014.06

ISSN  0897-4756

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Direction Control of Oriented Self-Assembly for 1D, 2D, and 3D Microarrays of Anisotropic Rectangular Nanoblocks

Nakagawa, Y; Kageyama, H; Oaki, Y; Imai, H

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 136 ( 10 ) 3716 - 3719 2014.03

ISSN  0002-7863

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鉄酸化細菌を模倣したプロセスによる多様な酸化鉄の合成と応用

OAKI Yuya

セラミックス 49   446 - 449 2014

Joint Work, Accepted

バイオミネラリゼーションを応用した有機／無機複合材料の開発とこれからの研究開発テーマ

OAKI Yuya

研究開発リーダー 1   8 - 12 2014

Research paper (scientific journal), Joint Work, Accepted

Basicity-controlled synthesis of Li₄Ti₅O₁₂ nanocrystals by a solvothermal method

Kageyama, H; Oaki, Y; Imai, H

RSC ADVANCES 4 ( 83 ) 44124 - 44129 2014

ISSN  2046-2069

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Syntheses of LiCoO₂ Mesocrystals by Topotactic Transformation and Their Electrochemical Properties

Nakajima, K; Oaki, Y; Imai, H

CHEMPLUSCHEM 78 ( 11 ) 1379 - 1383 2013.11

ISSN  2192-6506

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Thin Films that Consist of CuO Mesocrystal Nanosheets: An Application of Microbial-Mineralization-Inspired Approaches to Thin-Film Formation

Ikeda, T; Oaki, Y; Imai, H

CHEMISTRY-AN ASIAN JOURNAL 8 ( 9 ) 2064 - 2069 2013.09

ISSN  1861-4728

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Formation of trigonal microarrays with cubic Ba(NO₃)₂ in a polymer matrix

Ise, R; Oaki, Y; Imai, H

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 121 ( 1415 ) 555 - 558 2013.07

ISSN  1882-0743

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Spontaneous Formation of Two-Dimensional Micropatterns with Straight and/or Curving Dendrites through Crystal Growth of Ba(NO₃)₂ in Polymer Matrix

Tokutomi, D; Ise, R; Oaki, Y; Imai, H

CRYSTAL GROWTH & DESIGN 13 ( 7 ) 3011 - 3017 2013.07

ISSN  1528-7483

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Formation of Nanostructured MnO/Co/SolidElectrolyte Interphase Ternary Composites as a Durable Anode Material for Lithium-Ion Batteries

Dang, F; Oaki, Y; Kokubu, T; Hosono, E; Zhou, HS; Imai, H

CHEMISTRY-AN ASIAN JOURNAL 8 ( 4 ) 760 - 764 2013.04

ISSN  1861-4728

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Low-temperature syntheses of cubic BaTiO₃ nanoparticles in highly basic aqueous solution

Kageyama, H; Oaki, Y; Takezawa, Y; Suzuki, T; Imai, H

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 121 ( 1412 ) 388 - 392 2013.04

ISSN  1882-0743

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Monolayered Nanodots of Transition Metal Oxides

Keisuke Nakamura, Yuya Oaki and Hiroaki Imai

J. Am. Chem. Soc 135   4501 - 4508 2013

Research paper (scientific journal), Joint Work, Accepted

Monolayered Nanodots of Transition Metal Oxides

Keisuke Nakamura, *Yuya Oaki, and *Hiroaki Imai

Journal of the American Chemical Society 135   4501-4508 2013

Research paper (scientific journal), Joint Work, Accepted

A Microbial-Mineralization Approach for Syntheses of Iron Oxides with a High Specific Surface Area

Naoki Yagita, *Yuya Oaki, and *Hiroaki Imai

Chemistry–A European Journal 19   4419-4422 2013

Research paper (scientific journal), Joint Work, Accepted

Low-temperature syntheses of cubic BaTiO3 nanoparticles in highly basic aqueous solution

Hiroyuki Kageyama, Yuya Oaki, Yoko Takezawa, Toshimasa Suzuki and *Hiroaki Imai

Journal of the Ceramic Society of Japan 121   388-392 2013

Research paper (scientific journal), Joint Work, Accepted

Synthesis of Li–Mn–O Mesocrystals with Controlled Crystal Phases through Topotactic Transformation of MnCO3

Feng Dang, Tatsuhiko Hoshino, Yuya Oaki, *Eiji Hosono, *Haoshen Zhou, and *Hiroaki Imai

Nanoscale  2013

Research paper (scientific journal), Joint Work, Accepted

Formation of Nanostructured MnO/Co/Solid–Electrolyte Interphase Ternary Composites as a Durable Anode Material for Lithium-Ion Batteries

Feng Dang, Yuya Oaki, Takao Kokubu, *Eiji Hosono, *Haoshen Zhou, and *Hiroaki Imai

Chemistry–An Asian Journal  2013

Research paper (scientific journal), Joint Work, Accepted

バイオミネラルにまなぶ材料化学

OAKI Yuuya

農業機械学会誌 75 ( 1 ) 4-10 2013

Research paper (scientific journal), Joint Work, Accepted

Formation of Nanostructured MnO/Co/Solid–Electrolyte Interphase Ternary Composites as a Durable Anode Material for Lithium-Ion Batteries

Feng Dang, Yuya Oaki, Takao Kokubu, Eiji Hosono, Haoshen Zhou, and Hiroaki Imai

Chemistry–An Asian Journal 8   760 - 764 2013

Research paper (scientific journal), Joint Work, Accepted

A Microbial-Mineralization Approach for Syntheses of Iron Oxides with a High Specific Surface Area

Naoki Yagita, Yuya Oaki and Hiroaki Imai

Chemistry–A European Journal 19   4419 - 4422 2013

Research paper (scientific journal), Joint Work, Accepted

Thin Film of CuO Mesocrystal Nanosheets: Microbial-Mineralization-Inspired Approaches Applied to Formation of Thin Films

Tatsuya Ikeda, Yuya Oaki and Hiroaki Imai,

Chem. Asian J 8   2064 - 2069 2013

Research paper (scientific journal), Accepted

A Microbial-Mineralization-Inspired Approach for Systematic Syntheses of Copper Oxides with Controlled Morphologies in an Aqueous Solution at Room Temperature

Yuya Oaki, Tatsuya Ikeda and Hiroaki Imai

Bull. Chem. Soc. Jpn. 86 ( 7 ) 821 - 828 2013

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0009-2673

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Synthesis of Li-Mn-O mesocrystals with controlled crystal phases through topotactic transformation of MnCO₃

Dang, F; Hoshino, T; Oaki, Y; Hosono, E; Zhou, HS; Imai, H

NANOSCALE 5 ( 6 ) 2352 - 2357 2013

ISSN  2040-3364

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Artificial peptides binding to the <i>c</i> face of hydroxyapatite obtained by molecular display technology

Ono, S; Tsuji, T; Oaki, Y; Imai, H

RSC ADVANCES 3 ( 6 ) 1885 - 1889 2013

ISSN  2046-2069

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Recent advances in mesocrystals and their related structures

Oaki, Y; Imai, H

NANOSCIENCE, VOL 1: NANOSTRUCTURES THROUGH CHEMISTRY 1   1 - 28 2013

ISSN  2049-3541

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Microscale pin holders of β-Co(OH)₂ and LiCoO₂ having a single-crystalline feature

Nakajima, K; Oaki, Y; Imai, H

CRYSTENGCOMM 15 ( 33 ) 6465 - 6468 2013

ISSN  1466-8033

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Band-gap expansion of tungsten oxide quantum dots synthesized in sub-nano porous silica

Watanabe, H; Fujikata, K; Oaki, Y; Imai, H

CHEMICAL COMMUNICATIONS 49 ( 76 ) 8477 - 8479 2013

ISSN  1359-7345

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Spontaneous Formation of Sinuous and Wavy Micropatterns with Helical Growth of CuSO₄•5H₂O in Polymer Matrix

Ise, R; Oaki, Y; Imai, H

CRYSTAL GROWTH & DESIGN 12 ( 9 ) 4397 - 4402 2012.09

ISSN  1528-7483

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Self-organization of hollow-cone carbonate crystals through molecular control with an acid organic polymer

Oaki, Y; Adachi, R; Imai, H

POLYMER JOURNAL 44 ( 6 ) 612 - 619 2012.06

ISSN  0032-3896

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Versatile Modification for Highly Dispersive and Functionalized Mesoporous Silica Nanoparticles

Ukigaya, K; Oaki, Y; Imai, H

CHEMISTRY LETTERS 41 ( 5 ) 507 - 509 2012.05

ISSN  0366-7022

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Electrically Guided Microweb Formation with Ag Nanofibers under UV Irradiation and Its Application to Electrochemical and Plasmonic Devices

Takeji, M; Oaki, Y; Imai, H

JOURNAL OF PHYSICAL CHEMISTRY C 116 ( 10 ) 6103 - 6107 2012.03

ISSN  1932-7447

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Homogeneous and Disordered Assembly of Densely Packed Titanium Oxide Nanocrystals: An Approach to Coupled Synthesis and Assembly in Aqueous Solution

Oaki Yuya, Nakamura Keisuke, Imai Hiroaki

CHEMISTRY-A EUROPEAN JOURNAL 18 ( 10 ) 2825 - 2831 2012.03

ISSN  0947-6539

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Oriented Nanocrystal Mosaic in Monodispersed CaCO₃ Microspheres with Functional Organic Molecules

Imai, H; Tochimoto, N; Nishino, Y; Takezawa, Y; Oaki, Y

CRYSTAL GROWTH & DESIGN 12 ( 2 ) 876 - 882 2012.02

ISSN  1528-7483

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One-Pot Aqueous Solution Syntheses of Iron Oxide Nanostructures with Controlled Crystal Phases through a Microbial-Mineralization-Inspired Approach

Oaki Yuya, Yagita Naoki, Imai Hiroaki

CHEMISTRY-A EUROPEAN JOURNAL 18 ( 1 ) 110 - 116 2012.01

ISSN  0947-6539

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バイオミネラリゼーションにならう無機結晶の合成―分子制御による構造構築―

OAKI Yuuya

高分子 62 ( 2月 ) 79-81 2012

Research paper (scientific journal), Joint Work, Accepted

Self-Organization of Hollow-Coned Carbonate Crystals through Molecular Control by Using an Acid Organic Polymer

Yuya Oaki, Ryota Adachi, and *Hiroaki Imai

Polymer Journal 44   612-619 2012

Research paper (scientific journal), Joint Work, Accepted

Synthesis and Morphogenesis of Organic and Inorganic Polymers by Means of Biominerals and Biomimetic Materials

Misako Kijima, *Yuya Oaki, Yurika Munekawa, and *Hiroaki Imai

Chemistry–A European Journal 19 ( 7 ) 2284–2293 - 2293 2012

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0947-6539

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Biologically Synthesized or Bioinspired Process-Derived Iron Oxides as Catalysts for Living Cationic Polymerization of Vinyl Ether

Arihiro Kanazawa, Shokyoku Kanaoka, Naoki Yagita, Yuya Oaki, *Hiroaki Imai, Mayumi Oda, *Atsushi Arakaki, Tadashi Matsunaga, and *Sadahito Aoshima

Chemical Communications 48   10904–10906 2012

Research paper (scientific journal), Joint Work, Accepted

Enhanced Photoconductive Properties on a Simple Composite Coaxial Nanostructure of Zinc Oxide and Polypyrrole

*Yuya Oaki, Takahiro Oki, and *Hiroaki Imai

Journal of Materials Chemistry 22   21195–21200 2012

Research paper (scientific journal), Joint Work, Accepted

Morphology and Orientation Control of Guanine Crystals: A Biogenic Architecture and Its Structure Mimetics

*Yuya Oaki, Soichiro Kaneko, and *Hiroaki Imai

Journal of Materials Chemistry 22 ( 42 ) 22686–22691 - 22691 2012

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0959-9428

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ZnO nano-rectangular framework-like structure from zinc hydroxide acetate plates

Eiji Hosono, Takashi Tokunaga, Shintaro Ueno, Yuya Oaki, Hiroaki Imai, *Haoshen Zhou, and *Sinobu Fujihara,

Journal of the Ceramics Society of Japan 120 ( 1401 ) 171-174 - 174 2012

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1882-0743

• Access to Document (DOI)

Crystal-Growth Process of Single-Crystal-like Mesoporous ZnO through a Competitive Reaction in Solution

Eiji Hosono, Takashi Tokunaga, Shintaro Ueno, Yuya Oaki, Hiroaki Imai, *Haoshen Zhou, and *Sinobu Fujihara

Crystal Growth & Design 12 ( 6 ) 2923-2931 - 2931 2012

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1528-7483

• Access to Document (DOI)

Spontaneous Formation of Sinuous and Wavy Micropatterns with Helical Growth of CuSO4•5H2O in Polymer Matrix

Ryuta Ise, Yuya Oaki, and *Hiroaki Imai

Crystal Growth & Design 12   4397-4402 2012

Research paper (scientific journal), Joint Work, Accepted

Twisted growth of organic crystal in a polymer matrix: sigmoidal and helical morphologies of pyrene

Soichiro Ibe, Ryuta Ise, Yuya Oaki, and *Hiroaki Imai

CrystEngComm 14 ( 21 ) 7444-7449 - 7449 2012

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1466-8033

• Access to Document (DOI)

Artificial peptides binding to the c face of hydroxyapatite obtained by molecular display

Shohei Ono, Toru Tsuji, Yuya Oaki, and *Hiroaki Imai

RSC Advances 3   1885-1889 2012

Research paper (scientific journal), Joint Work, Accepted

バイオミネラリゼーションにならう酸化物合成プロセス

OAKI Yuuya

機能材料 32   48-55 2012

Research paper (scientific journal), Joint Work, Accepted

Enhanced photoconductive properties of a simple composite coaxial nanostructure of zinc oxide and polypyrrole

Oaki Yuya, Oki Takahiro, Imai Hiroaki

JOURNAL OF MATERIALS CHEMISTRY 22 ( 39 ) 21195 - 21200 2012

ISSN  0959-9428

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Biologically synthesized or bioinspired process-derived iron oxides as catalysts for living cationic polymerization of a vinyl ether

Kanazawa, A; Kanaoka, S; Yagita, N; Oaki, Y; Imai, H; Oda, M; Arakaki, A; Matsunaga, T; Aoshima, S

CHEMICAL COMMUNICATIONS 48 ( 88 ) 10904 - 10906 2012

ISSN  1359-7345

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Morphological variation of hydroxyapatite grown in aqueous solution based on simulated body fluid

Kobayashi, T; Ono, S; Hirakura, S; Oaki, Y; Imai, H

CRYSTENGCOMM 14 ( 3 ) 1143 - 1149 2012

ISSN  1466-8033

• Access to Document (DOI)

Mesocrystal nanosheet of rutile TiO₂ and its reaction selectivity as a photocatalyst

Aoyama, Y; Oaki, Y; Ise, R; Imai, H

CRYSTENGCOMM 14 ( 4 ) 1405 - 1411 2012

ISSN  1466-8033

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Biomimetic Solid-Solution Precursors of Metal Carbonate for Nanostructured Metal Oxides: MnO/Co and MnO-CoO Nanostructures and Their Electrochemical Properties

Kokubu, T; Oaki, Y; Hosono, E; Zhou, HS; Imai, H

ADVANCED FUNCTIONAL MATERIALS 21 ( 19 ) 3673 - 3680 2011.10

ISSN  1616-301X

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Control of cellular activity of osteoblastic cells with microtopography of biphasic calcium phosphate scaffolds

Okada, S; Oaki, Y; Komotori, J; Imai, H

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 119 ( 1392 ) 635 - 639 2011.08

ISSN  1882-0743

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Synthesis and Morphogenesis of Organic Polymer Materials with Hierarchical Structures in Biominerals

Oaki Yuya, Kijima Misako, Imai Hiroaki

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 ( 22 ) 8594 - 8599 2011.06

ISSN  0002-7863

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Control of cellular activity of fibroblasts on size-tuned fibrous hydroxyapatite nanocrystals

Okada, S; Nagai, A; Oaki, Y; Komotori, J; Imai, H

ACTA BIOMATERIALIA 7 ( 3 ) 1290 - 1297 2011.03

ISSN  1742-7061

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In Vitro Repair of a Biomineral with a Mesocrystal Structure

Kijima, M; Oaki, Y; Imai, H

CHEMISTRY-A EUROPEAN JOURNAL 17 ( 10 ) 2828 - 2832 2011.03

ISSN  0947-6539

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A Microbial-Mineralization-Inspired Approach for Synthesis of Manganese Oxide Nanostructures with Controlled Oxidation States and Morphologies

Oba, M; Oaki, Y; Imai, H

ADVANCED FUNCTIONAL MATERIALS 20 ( 24 ) 4279 - 4286 2010.12

ISSN  1616-301X

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Homogeneous and Disordered Assembly of Densely Packed Nanocrystals

Oaki, Y; Anzai, T; Imai, H

ADVANCED FUNCTIONAL MATERIALS 20 ( 23 ) 4127 - 4132 2010.12

ISSN  1616-301X

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Fibrous nanocrystals of hydroxyapatite loaded with TiO₂ nanoparticles for the capture and photocatalytic decomposition of specific proteins

Hirakura, S; Kobayashi, T; Ono, S; Oaki, Y; Imai, H

COLLOIDS AND SURFACES B-BIOINTERFACES 79 ( 1 ) 131 - 135 2010.08

ISSN  0927-7765

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Synthesis and Applications of SnO Nanosheets: Parallel Control of Oxidation State and Nanostructure Through an Aqueous Solution Route

Sakaushi, K; Oaki, Y; Uchiyama, H; Hosono, E; Zhou, HS; Imai, H

SMALL 6 ( 6 ) 776 - 781 2010.03

ISSN  1613-6810

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Specific Photocatalytic Performance of Nanostructured Rutile-Type TiO₂: Selective Oxidation of Thiazin Dye with a Bundled Architecture Consisting of Oriented Nanoneedles

Tokunaga, Y; Uchiyama, H; Oaki, Y; Imai, H

SCIENCE OF ADVANCED MATERIALS 2 ( 1 ) 69 - 73 2010.03

ISSN  1947-2935

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Aqueous solution synthesis of SnO nanostructures with tuned optical absorption behavior and photoelectrochemical properties through morphological evolution

Sakaushi, K; Oaki, Y; Uchiyama, H; Hosono, E; Zhou, HS; Imai, H

NANOSCALE 2 ( 11 ) 2424 - 2430 2010

ISSN  2040-3364

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Enhanced photocatalytic activity of quantum-confined tungsten trioxide nanoparticles in mesoporous silica

Tanaka, D; Oaki, Y; Imai, H

CHEMICAL COMMUNICATIONS 46 ( 29 ) 5286 - 5288 2010

ISSN  1359-7345

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Emergence of helical morphologies with crystals: twisted growth under diffusion-limited conditions and chirality control with molecular recognition

Imai, H; Oaki, Y

CRYSTENGCOMM 12 ( 6 ) 1679 - 1687 2010

ISSN  1466-8033

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Biomimetic Synthesis of Metal Ion-Doped Hierarchical Crystals Using a Gel Matrix: Formation of Cobalt-Doped LiMn₂O₄ with Improved Electrochemical Properties through a Cobalt-Doped MnCO₃ Precursor

Kokubu, T; Oaki, Y; Uchiyama, H; Hosono, E; Zhou, HS; Imai, H

CHEMISTRY-AN ASIAN JOURNAL 5 ( 4 ) 792 - 798 2010

ISSN  1861-4728

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Photochemical Reactions in Nanoscopic Organic Domains Generated from Oriented Crystals with Polymers: Nanocrystalline Mosaics as a New Family of Host Materials

Oaki Yuya, Imai Hiroaki

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 82 ( 5 ) 613 - 617 2009.05

ISSN  0009-2673

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Magnesium-Mediated Nanocrystalline Mosaics of Calcite

Nishino, Y; Oaki, Y; Imai, H

CRYSTAL GROWTH & DESIGN 9 ( 1 ) 223 - 226 2009.01

ISSN  1528-7483

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Nanosegregated Amorphous Composites of Calcium Carbonate and an Organic Polymer

Oaki Yuya, Kajiyama Satoshi, Nishimura Tatsuya, Imai Hiroaki, Kato Takashi

ADVANCED MATERIALS 20 ( 19 ) 3633 - + 2008.10

ISSN  0935-9648

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Formation of ε-Fe₂O₃ nanocrystals through segregation in mesoporous silica particles

Mori, K; Oaki, Y; Suda, M; Einaga, Y; Imai, H

CHEMISTRY LETTERS 37 ( 8 ) 814 - 815 2008.08

ISSN  0366-7022

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Selective synthesis of various nanoscale morphologies of hydroxyapatite via an intermediate phase

Ito, H; Oaki, Y; Imai, H

CRYSTAL GROWTH & DESIGN 8 ( 3 ) 1055 - 1059 2008.03

ISSN  1528-7483

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Stereospecific morphogenesis of aspartic acid helical crystals through molecular recognition

Oaki, Y; Imai, H

LANGMUIR 23 ( 10 ) 5466 - 5470 2007.05

ISSN  0743-7463

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A hierarchical self-similar structure of oriented calcite with association of an agar gel matrix: inheritance of crystal habit from nanoscale

Oaki Yuya, Hayashi Shinichiro, Imai Hiroaki

CHEMICAL COMMUNICATIONS  ( 27 ) 2841 - 2843 2007

ISSN  1359-7345

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One-pot synthesis of manganese oxide nanosheets in aqueous solution: Chelation-mediated parallel control of reaction and morphology

Oaki Yuya, Imai Hiroaki

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 46 ( 26 ) 4951 - 4955 2007

ISSN  1433-7851

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Chelation-mediated aqueous synthesis of metal oxyhydroxide and oxide nanostructures: Combination of ligand-controlled oxidation and ligandcooperative morphogenesis

Oaki Yuya, Imai Hiroaki

CHEMISTRY-A EUROPEAN JOURNAL 13 ( 30 ) 8564 - 8571 2007

ISSN  0947-6539

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Biomimetic morphological design for manganese oxide and cobalt hydroxide nanoflakes with a mosaic interior

Oaki, Y; Imai, H

JOURNAL OF MATERIALS CHEMISTRY 17 ( 4 ) 316 - 321 2007

ISSN  0959-9428

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A biomimetic approach for hierarchically structured inorganic crystals through self-organization

Imai, H; Oaki, Y; Kotachi, A

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 79 ( 12 ) 1834 - 1851 2006.12

ISSN  0009-2673

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Biomimetic synthesis of wurtzite ZnO nanowires possessing a mosaic structure

Yahiro, J; Oaki, Y; Imai, H

SMALL 2 ( 10 ) 1183 - 1187 2006.10

ISSN  1613-6810

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Incorporation of dyes into silica-surfactant mesostructured nanoparticles as a nanoscale host material for organic molecules

Muto, S; Oaki, Y; Imai, H

CHEMISTRY LETTERS 35 ( 8 ) 880 - 881 2006.08

ISSN  0366-7022

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Bridged nanocrystals in biominerals and their biomimetics: Classical yet modern crystal growth on the nanoscale

Oaki, Y; Kotachi, A; Miura, T; Imai, H

ADVANCED FUNCTIONAL MATERIALS 16 ( 12 ) 1633 - 1639 2006.08

ISSN  1616-301X

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Room-temperature aqueous synthesis of highly luminescent BaWO4-polymer nanohybrids and their spontaneous conversion to hexagonal WO3 nanosheets

Oaki Yuya, Imai Hiroaki

ADVANCED MATERIALS 18 ( 14 ) 1807 - + 2006.07

ISSN  0935-9648

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Preparation of hierarchically organized calcium phosphate-organic polymer composites by calcification of hydrogel

Furuichi, K; Oaki, Y; Ichimiya, H; Komotori, J; Imai, H

SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 7 ( 2 ) 219 - 225 2006.03

ISSN  1468-6996

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Emergence of acute morphologies consisting of iso-oriented calcite nanobricks in a binary poly(acrylic acid) system

Miura, T; Kotachi, A; Oaki, Y; Imai, H

CRYSTAL GROWTH & DESIGN 6 ( 2 ) 612 - 615 2006.02

ISSN  1528-7483

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Preparation of nanotextured and nanoribrous hydroxyapatite through dicalcium phosphate with gelatin

Furuichi, K; Oaki, Y; Imai, H

CHEMISTRY OF MATERIALS 18 ( 1 ) 229 - 234 2006.01

ISSN  0897-4756

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Nanoengineering in echinoderms: The emergence of morphology from nanobricks

Oaki, Y; Imai, H

SMALL 2 ( 1 ) 66 - 70 2006.01

ISSN  1613-6810

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A novel adsorbent photocatalyst consisting of titania and mesoporous silica nanoparticles

Uchiyama, H; Suzuki, K; Oaki, Y; Imai, H

MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY 123 ( 3 ) 248 - 251 2005.11

ISSN  0921-5107

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Hierarchically organized superstructure emerging from the exquisite association of inorganic crystals, organic polymers, and dyes: A model approach towards suprabiomineral materials

Oaki, Y; Imai, H

ADVANCED FUNCTIONAL MATERIALS 15 ( 9 ) 1407 - 1414 2005.09

ISSN  1616-301X

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Morphological evolution of inorganic crystal into zigzag and helical architectures with an exquisite association of polymer: A novel approach for morphological complexity

Oaki, Y; Imai, H

LANGMUIR 21 ( 3 ) 863 - 869 2005.02

ISSN  0743-7463

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Hierarchically organized architecture of potassium hydrogen phthalate and poly(acrylic acid): toward a general strategy for biomimetic crystal design

Oaki, Y; Imai, H

CHEMICAL COMMUNICATIONS  ( 48 ) 6011 - 6013 2005

ISSN  1359-7345

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Amplification of chirality from molecules into morphology of crystals through molecular recognition

Oaki Y, Imai H

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 126 ( 30 ) 9271 - 9275 2004.08

ISSN  0002-7863

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Emergence of morphological chirality from twinned crystals

Imai, H; Oaki, Y

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 43 ( 11 ) 1363 - 1368 2004

ISSN  1433-7851

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Experimental demonstration for the morphological evolution of crystals grown in gel media

Oaki, Y; Imai, H

CRYSTAL GROWTH & DESIGN 3 ( 5 ) 711 - 716 2003.09

ISSN  1528-7483

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Formation of calcium phosphate having a hierarchically laminated architecture through periodic precipitation in organic gel

Imai, H; Tatara, S; Furuichi, K; Oaki, Y

CHEMICAL COMMUNICATIONS  ( 15 ) 1952 - 1953 2003

ISSN  1359-7345

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