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Papers - Oaki, Yuya

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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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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