Details of a Researcher

Papers - Oaki, Yuya

Division display 61 - 80 of about 302 ／ All the affair displays >>

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

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.

Access to Document (DOI)

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) 11 ( 2 ) 2023

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.

Access to Document (DOI)

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) 10 ( 34 ) 2023

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.

Access to Document (DOI)

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) 39 ( 42 ) 14984 - 14995 2023

ISSN 07437463

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

Access to Document (DOI)

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

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.

Access to Document (DOI)

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

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

Access to Document (DOI)

　 Previous page - Next page 　