Papers - Imai, Hiroaki

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 ) 319 - 326 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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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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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   8997 - 9001 2017.12

Research paper (scientific journal), Joint Work, Accepted

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

今井 宏明

R. Matsumoto, Y. Nakagawa, K. Kato, Y. Oaki, H. Imai (Langmuir)  33   13805 - 13810 2017.12

Research paper (scientific journal), Joint Work, Accepted

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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   7191 - 7196 2017.11

Research paper (scientific journal), Joint Work, Accepted

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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   825 - 830 2017.10

Research paper (scientific journal), Joint Work, Accepted

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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   12123 - 12130 2017.10

Research paper (scientific journal), Joint Work, Accepted

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

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

Chemical Science 8   647 - 653 2017.08

Research paper (scientific journal), Joint Work, Accepted

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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   8250 - 8255 2017.07

Research paper (scientific journal), Joint Work, Accepted

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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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Dispersion of Hydroxyapatite Nanocrystals Stabilized by Polymeric Molecules Bearing Carboxy and SulfoGroups

K. Watanabe, I. Nishida, H. Imai

Colloid and Polymer Science 295   1491 - 1498 2017.06

Research paper (scientific journal), Joint Work, Accepted

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   7329 - 7332 2017.05

Research paper (scientific journal), Joint Work, Accepted

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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   3694 - 3699 2017.05

Research paper (scientific journal), Joint Work, Accepted

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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 2017.04

Research paper (scientific journal), Joint Work, Accepted

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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   16546 - 16552 2017.04

Research paper (scientific journal), Joint Work, Accepted

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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. Ima

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

Research paper (scientific journal), Joint Work, Accepted

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Phase separation through simultaneous polymerization and crystallization for composite materials, Asian Materials

K. Sato, Y. Oaki, H. Imai

MPG Asia Materials 9   e377 2017.04

Research paper (scientific journal), Joint Work, Accepted

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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    935 - 941 2017.04

Joint Work, Accepted

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