Papers - Oaki, Yuya

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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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