Updated on 2024/09/30

Information

 

写真a

 
HIGUCHI YUJI
 
Organization
Research Institute for Information Technology Associate Professor
Title
Associate Professor
Profile
To realize a new data-driven material design based on statistical physics, it is necessary to understand the structure and dynamics of materials from a molecular theory. Through molecular simulations and large-scale calculations, I have studied the physical properties and structures of polymers, biomolecules, biomaterials, ceramic materials, etc. For soft matter materials, it was difficult to model the complex structure of the actual material, and the elucidation of the physical properties on the molecular scale was delayed compared to the macroscopic experimental facts. Since soft matter is a collection of molecules that express structures and functions and has a hierarchically ordered structure, it is necessary to understand the structure and physical properties widely from the molecular level to the mesoscale. Furthermore, many components determine the system. Therefore, clarifying which component is important and at which scale, is essential to understand the phenomenon. In actual materials, I think that considering the detailed structure of the atomic scale, the difference in composition, and the electronic states are needed to understand the structure and physical properties of molecular aggregates. Thus, I have performed multi-scale modeling and simulation using quantum chemistry calculations, all-atom simulations, and coarse-grained simulations based on chemistry, engineering, physics, and information science.

Degree

  • Ph.D. (Science)

Research History

  • 2011年4月-2015年3月 東北大学大学院工学研究科 助教 2015年4月-2017年3月 東北大学金属材料研究所 助教 2013年10月-2017年3月 科学技術振興機構さきがけ研究員・兼任 2017年4月- 2022年3月 東京大学物性研究所 助教   

Research Interests・Research Keywords

  • Research theme: Molecular simulations and large-scale calculations on soft matter

    Keyword: Polymer, Soft matter, Molecular simulations, Large-scale calculation

    Research period: 2022.4

Awards

  • 第18回(2024年)日本物理学会若手奨励賞(領域12)

    2024.3   日本物理学会   Young Scientist Award of the Physical Society of Japan

  • Young Scientist Award of the Physical Society of Japan

    2024.3   The Physical Society of Japan   分子シミュレーションによるソフトマターの構造・物性の理解

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  • 第36回計算力学講演会(CMD2023)優秀講演表彰

    2023.12   日本機械学会   高分子材料の変形・破壊に関する粗視化分子動力学シミュレーション

  • Outstanding Presentation Award

    2021.11   日本シミュレーション学会   Outstanding Presentation Award

  • 2021年度分子シミュレーション学会学術賞

    2021.11   分子シミュレーション学会   The Molecular Simulation Society of Japan Award

Papers

  • Reversibility of Semicrystalline Polymers in Creep Testing by Coarse‐Grained Molecular Dynamics Simulations Reviewed

    Yuji Higuchi, Go Matsuba

    Macromolecular Chemistry and Physics   2024.7   ISSN:1022-1352 eISSN:1521-3935

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    Publishing type:Research paper (scientific journal)   Publisher:Wiley  

    Abstract

    Unraveling the deformation processes of semicrystalline polymers is essential for improving their durability. Owing to their hierarchical structures composed of lamellae and spherulites, many aspects of these deformation processes remain unclear at the molecular scale, such as the differences in molecular structure changes in the elastic and plastic regions and the molecular‐scale structural changes during reversible and irreversible processes. Herein, simulated creep tests of the lamellar structure of polyethylene under a constant load are performed using the coarse‐grained molecular dynamics method. Typical creep curves are observed, confirming the validity of the simulation results. During the recovery process after stretching, the reversible and irreversible processes are distinguished by a strain of approximately 0.4 at the boundary of the elastic and plastic regions. Interestingly, during recovery, the interfaces between the amorphous and crystalline layers are highly oriented, which may inhibit strain relaxation. In terms of the molecular structure changes in the elastic region, the number of tie chains remains constant, whereas the numbers of chain ends and loops in the amorphous layers decrease. These simulation results advance current understanding of the molecular‐scale deformation processes of semicrystalline polymers, which contribute to the improvement of long‐term durability and reliability.

    This article is protected by copyright. All rights reserved

    DOI: 10.1002/macp.202400076

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  • Rotational Dynamics of Water near Osmolytes by Molecular Dynamics Simulations Reviewed

    Yuji Higuchi, Md. Abu Saleh, Takahisa Anada, Masaru Tanaka, Mafumi Hishida

    The Journal of Physical Chemistry B   128 ( 20 )   5008 - 5017   2024.5   ISSN:1520-6106 eISSN:1520-5207

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    The behavior of water molecules around organic molecules has attracted considerable attention as a crucial factor influencing the properties and functions of soft matter and biomolecules. Recently, it has been suggested that the change in protein stability upon the addition of small organic molecules (osmolytes) is dominated by the change in the water dynamics caused by the osmolyte, where the dynamics of not only the directly interacting water molecules but also the long-range hydration layer affect the protein stability. However, the relation between the long-range structure of hydration water in various solutions and the water dynamics remains unclear at the molecular level. We performed density-functional tight-binding molecular dynamics simulations to elucidate the varying rotational dynamics of water molecules in 15 osmolyte solutions. A positive correlation was observed between the rotational relaxation time and our proposed normalized parameter obtained by dividing the number of hydrogen bonds between water molecules by the number of nearest-neighbor water molecules. For the 15 osmolyte solutions, an increase or a decrease in the value of the normalized parameter for the second hydration shell tended to result in water molecules with slow and fast rotational dynamics, respectively, thus illustrating the importance of the second hydration shell for the rotational dynamics of water molecules. Our simulation results are anticipated to advance the current understanding of water dynamics around organic molecules and the long-range structure of water molecules.

    DOI: 10.1021/acs.jpcb.3c08470

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  • Absorption of water molecules on the surface of stereocomplex-crystal spherulites of polylactides: An in-situ FT-IR spectroscopy investigation Reviewed

    Tomoka Kokuzawa, Shunryu Hirabayashi, Yuka Ikemoto, Junsu Park, Ryohei Ikura, Yoshinori Takashima, Yuji Higuchi, Go Matsuba

    Polymer   298   126922 - 126922   2024.4   ISSN:0032-3861 eISSN:1873-2291

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    Language:Others   Publishing type:Research paper (scientific journal)   Publisher:Elsevier BV  

    The correlation between water molecules and polylactide was clarified. The crystallinity in stereocomplex (SC) crystal spherulites was investigated using microbeam wide-angle X-ray diffraction. The crystallinity was higher in the central region, and edge-on lamellae grew in a twisted manner. The hydrogen bonding in SC-crystal spherulites was evaluated via microbeam FT-IR spectroscopy in a humidity-controlled cell. The water-derived bands corresponding to OH vibration and HOH bending increased with increasing humidity. Microbeam FT-IR spectroscopy was used to evaluate the water absorption behavior of crystalline films depending on their position. Coarse-grained molecular dynamics simulations indicated that the number of adsorbed water molecules increased with decreasing crystallinity. In SC-crystal spherulites, water molecules are absorbed in both amorphous and crystalline regions but with greater difficulty in the crystalline regions. These insights into water molecule absorption on SC-crystal spherulite can facilitate the development of polylactide materials with controlled biodegradability for advanced medical and optical applications.

    DOI: 10.1016/j.polymer.2024.126922

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  • Tribological Simulation of Polymer Materials Using Molecular Dynamics Method

    HIGUCHI Yuji, TAKAKUWA Ryo, OOTANI Yusuke, KUBO Momoji

    JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS   69 ( 3 )   195 - 202   2024.3   ISSN:09151168 eISSN:21899967

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    Authorship:Lead author   Language:Japanese   Publisher:Japanese Society of Tribologists  

    <p>With the development of high-performance computers, the importance of computer simulation is growing in tribology. In this article, we introduce the molecular dynamics-based tribology simulation method for polymer materials with our tribology simulation results for polymer brush.</p>

    DOI: 10.18914/tribologist.69.03_195

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  • Model Amphiphilic Polymer Conetworks in the Bulk: Dissipative Particle Dynamics Simulations of Their Self-Assembly and Mechanical Properties Reviewed

    Dimitrios G. Tsalikis, Mihai Ciobanu, Costas S. Patrickios, Yuji Higuchi

    Macromolecules   56 ( 23 )   9299 - 9311   2023.11   ISSN:0024-9297 eISSN:1520-5835

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    Model Amphiphilic Polymer Conetworks in the Bulk: Dissipative Particle Dynamics Simulations of Their Self-Assembly and Mechanical Properties

    DOI: 10.1021/acs.macromol.3c01392

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  • Lateral Transport of Domains in Anionic Lipid Bilayer Membranes under DC Electric Fields: A Coarse-Grained Molecular Dynamics Study Reviewed

    Hiroaki Ito, Naofumi Shimokawa, Yuji Higuchi

    The Journal of Physical Chemistry B   127 ( 41 )   8860 - 8868   2023.10   ISSN:1520-6106 eISSN:1520-5207

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    Dynamic lateral transport of lipids, proteins, and self-assembled structures in biomembranes plays a crucial role in diverse cellular processes. In this study, we perform coarse-grained molecular dynamics simulations on a vesicle composed of a binary mixture of neutral and anionic lipids to investigate the lateral transport of individual lipid molecules and the self-assembled lipid domains upon an applied direct current (DC) electric field. Under the potential force of the electric field, a phase-separated domain rich in anionic lipids is trapped in the opposite direction of the electric field. The subsequent reversal of the electric field induces unidirectional domain motion. During the domain motion, the domain size remains constant, but a considerable amount of the anionic lipids is exchanged between the anionic-lipid-rich domain and the surrounding bulk. While the speed of the domain motion (collective lipid motion) shows a significant positive correlation with the electric field strength, the exchange of anionic lipids between the domain and bulk (individual lipid motion) exhibits no clear correlation with the field strength. The mean velocity field of the lipids surrounding the domain displays a two-dimensional (2D) source dipole. We revealed that the balance between the potential force of the applied electric field and the quasi-2D hydrodynamic frictional force well explains the dependence of the domain motions on the electric field strengths. The present results provide insight into the hierarchical dynamic responses of self-assembled lipid domains to the applied electric field and contribute to controlling the lateral transportation of lipids and membrane inclusions.

    DOI: 10.1021/acs.jpcb.3c04351

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  • Organocatalyzed ring-opening reactions of γ-carbonyl-substituted ε-caprolactones Reviewed

    Takayuki Ota, Valentina Montagna, Yuji Higuchi, Takashi Kato, Masaru Tanaka, Haritz Sardon, Kazuki Fukushima

    RSC Advances   13 ( 40 )   27764 - 27771   2023.9   eISSN:2046-2069

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    γ-Carbonyl-substituted ε-caprolactones were found to predominantly isomerize to five-membered lactones rather than to form desired linear polyesters in ring-opening polymerization.

    DOI: 10.1039/d3ra01025b

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  • Quasi-elastic neutron scattering reveals the relationship between the dynamical behavior of phospholipid headgroups and hydration water Reviewed

    Md. Khalidur Rahman, Takeshi Yamada, Norifumi L. Yamada, Mafumi Hishida, Yuji Higuchi, Hideki Seto

    Structural Dynamics   10 ( 4 )   044701   2023.7   ISSN:2329-7778 eISSN:2329-7778

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    The dynamics of hydration water (HW) in 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) was investigated by means of quasi-elastic neutron scattering (QENS) and compared with those observed in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The headgroup dynamics of DMPE was investigated using a mixture of tail-deuterated DMPE and D2O, and the QENS profiles were interpreted as consisting of three modes. The fast mode comprised the rotation of hydrogen atoms in –NH3+ and –CH2– groups in the headgroup of DMPE, the medium-speed mode comprised fluctuations in the entire DMPE molecule, and the slow mode comprised fluctuations in the membrane. These interpretations were confirmed using molecular dynamics (MD) simulations. The HW dynamics analysis was performed on a tail-deuterated DMPE and H2O mixture. The QENS profiles were analyzed in terms of three modes: (1) a slow mode, identified as loosely bound HW in the DMPC membrane; (2) a medium-speed mode similar to free HW in the DMPC membrane; and (3) a fast mode, identified as rotational motion. The relaxation time for the fast mode was approximately six times shorter than that of rotational water in DMPC, consistent with the results of terahertz time-domain spectroscopy. The activation energy of medium-speed HW in DMPE differed from that of free HW in DMPC, suggesting the presence of different hydration states or hydrogen-bonded networks around the phosphocholine and phosphoethanolamine headgroups.

    DOI: 10.1063/4.0000184

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  • Coarse-grained molecular dynamics simulation of cation distribution profiles on negatively charged lipid membranes during phase separation Reviewed

    Yuji Higuchi, Klemen Bohinc, Jurij Reščič, Naofumi Shimokawa, Hiroaki Ito

    Soft Matter   19 ( 20 )   3640 - 3651   2023.5   ISSN:1744-683X eISSN:1744-6848

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    Correlation between the phase separation of membranes consisting of negatively charged and neutral phospholipids and cation distribution in aqueous solutions is presented.

    DOI: 10.1039/d3sm00222e

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  • Endocytosis-Like Vesicle Fission Mediated by a Membrane-Expanding Molecular Machine Enables Virus Encapsulation for In Vivo Delivery Reviewed

    Noriyuki Uchida, Yunosuke Ryu, Yuichiro Takagi, Ken Yoshizawa, Kotono Suzuki, Yasutaka Anraku, Itsuki Ajioka, Naofumi Shimokawa, Masahiro Takagi, Norihisa Hoshino, Tomoyuki Akutagawa, Teruhiko Matsubara, Toshinori Sato, Yuji Higuchi, Hiroaki Ito, Masamune Morita, Takahiro Muraoka

    Journal of the American Chemical Society   145 ( 11 )   6210 - 6220   2023.2   ISSN:0002-7863 eISSN:1520-5126

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    Biological membranes are functionalized by membrane-associated protein machinery. Membrane-associated transport processes, such as endocytosis, represent a fundamental and universal function mediated by membrane-deforming protein machines, by which small biomolecules and even micrometer-size substances can be transported via encapsulation into membrane vesicles. Although synthetic molecules that induce dynamic membrane deformation have been reported, a molecular approach enabling membrane transport in which membrane deformation is coupled with substance binding and transport remains critically lacking. Here, we developed an amphiphilic molecular machine containing a photoresponsive diazocine core (AzoMEx) that localizes in a phospholipid membrane. Upon photoirradiation, AzoMEx expands the liposomal membrane to bias vesicles toward outside-in fission in the membrane deformation process. Cargo components, including micrometer-size M13 bacteriophages that interact with AzoMEx, are efficiently incorporated into the vesicles through the outside-in fission. Encapsulated M13 bacteriophages are transiently protected from the external environment and therefore retain biological activity during distribution throughout the body via the blood following administration. This research developed a molecular approach using synthetic molecular machinery for membrane functionalization to transport micrometer-size substances and objects via vesicle encapsulation. The molecular design demonstrated in this study to expand the membrane for deformation and binding to a cargo component can lead to the development of drug delivery materials and chemical tools for controlling cellular activities.

    DOI: 10.1021/jacs.2c12348

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  • Anisotropic, Degradable Polymer Assemblies Driven by a Rigid Hydrogen-Bonding Motif That Induce Shape-Specific Cell Responses Reviewed

    Kazuki Fukushima, Kodai Matsuzaki, Masashi Oji, Yuji Higuchi, Go Watanabe, Yuki Suzuki, Moriya Kikuchi, Nozomi Fujimura, Naofumi Shimokawa, Hiroaki Ito, Takashi Kato, Seigou Kawaguchi, Masaru Tanaka

    Macromolecules   55 ( 1 )   15 - 25   2022.1   ISSN:0024-9297 eISSN:1520-5835

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    Poly(ethylene glycol)-conjugated amphiphilic block copolymers, which contain degradable hydrophobic blocks connected by a rigid hydrogen-bonding motif (RHM), are developed to yield anisotropic nanoassemblies in a manner independent of the crystalline nature of the hydrophobic block. The all-atom and coarse-grained molecular dynamics simulations suggest that the anisotropic alignment of the block copolymers can be attributed to the π-πinteractions of the RHM and the crystallizable hydrophobic blocks help maintain the aligned structure. Light scattering analysis of the polymer assemblies demonstrates the formation of nonspherical assemblies by the RHM-containing block copolymers with an amorphous hydrophobic block; this indicates the strong contribution of the RHM to the directed assembly of the block copolymers, unlike crystallization-driven self-assembly. Enhanced cell proliferation is observed in cell cultures containing normal human fibroblasts in the presence of the anisotropic polymer assemblies with aspect ratios greater than 12 or lengths greater than 310 nm.

    DOI: 10.1021/acs.macromol.1c01894

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  • Hydrophobic immiscibility controls self-sorting or co-assembly of peptide amphiphiles Reviewed

    Rie Wakabayashi, Rino Imatani, Mutsuhiro Katsuya, Yuji Higuchi, Hiroshi Noguchi, Noriho Kamiya, Masahiro Goto

    Chemical Communications   58 ( 4 )   585 - 588   2022.1   ISSN:1359-7345 eISSN:1364-548X

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    Self-sorting and co-assembly of aqueous supramolecular fibres were formed using peptide amphiphiles having immiscible hydrophobic tails.

    DOI: 10.1039/d1cc05560g

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  • Atom-by-Atom and Sheet-by-Sheet Chemical Mechanical Polishing of Diamond Assisted by OH Radicals: A Tight-Binding Quantum Chemical Molecular Dynamics Simulation Study Reviewed

    Kentaro Kawaguchi, Yang Wang, Jingxiang Xu, Yusuke Ootani, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    ACS Applied Materials & Interfaces   13 ( 34 )   41231 - 41237   2021.9

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    DOI: 10.1021/acsami.1c09468

  • Three-Phase Coexistence in Binary Charged Lipid Membranes in a Hypotonic Solution Reviewed

    Jingyu Guo, Hiroaki Ito, Yuji Higuchi, Klemen Bohinc, Naofumi Shimokawa, Masahiro Takagi

    Langmuir   37 ( 32 )   9683 - 9693   2021.8

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    DOI: 10.1021/acs.langmuir.1c00967

  • Role of OH Termination in Mitigating Friction of Diamond-like Carbon under High Load: A Joint Simulation and Experimental Study Reviewed

    Yang Wang, Kentaro Hayashi, Yusuke Ootani, Shandan Bai, Tomomi Shimazaki, Yuji Higuchi, Nobuki Ozawa, Koshi Adachi, Maria-Isabel De Barros Bouchet, Jean Michel Martin, Momoji Kubo

    Langmuir   37 ( 20 )   6292 - 6300   2021.5

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    Diamond-like carbon (DLC) has recently attracted much attention as a promising solid-state lubricant because it exhibits low friction, low abrasion, and high wear resistance. Although we previously reported the reason why H-terminated DLC exhibits low friction based on a tight-binding quantum chemical molecular dynamics (TB-QCMD) simulation, experimentally, the low-friction state of H-terminated DLC is not stable, limiting its application. In the present work, our TB-QCMD simulations suggest that H/OH-terminated DLC could give low friction even under high loads, whereas H-terminated DLC could not. By using gas-phase friction experiments, we confirm that OH termination can indeed provide much more stable lubricity than H termination, validating the predictions from simulations. We conclude that H/OH-terminated DLC is a new low-friction material with high load capacity and high stable lubricity that may be suitable for practical use in industrial applications.

    DOI: 10.1021/acs.langmuir.1c00727

  • Rotational Dynamics of Water at the Phospholipid Bilayer Depending on the Head Groups Studied by Molecular Dynamics Simulations Reviewed

    Yuji Higuchi, Yuta Asano, Takuya Kuwahara, Mafumi Hishida

    Langmuir   37 ( 17 )   5329 - 5338   2021.5

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    Hydration states are a crucial factor that affect the self-assembly and properties of soft materials and biomolecules. Although previous experiments have revealed that the hydration state strongly depends on the chemical structure of lipid molecules, the mechanisms at the molecular level remain unknown. Classical and density-functional tight-binding (DFTB) molecular dynamics (MD) simulations are employed to determine the mechanisms underlying dissimilar water dynamics between lipid membranes with phosphatidylcholine (PC) and phosphatidylethanolamine (PE) head groups. The classical MD simulation shows that rotational relaxations of water are faster on the PE lipid than on the PC lipid, which is consistent with a previous experimental study using terahertz spectroscopy. Furthermore, DFTB-MD simulation of N(CH3)(4)(+) and NH4+ ions, which correspond to the different head groups in PC and PE, respectively, shows qualitative agreement with the classical MD simulation. Remarkably, the PE lipids and the NH4(+) ions break hydrogen bonds between water molecules in the secondary hydration shell. In contrast, the PC lipids and the N(CH3)(4)(+) ions bind water molecules weakly in both the primary and secondary hydration shells and increase hydrogen bonds between water. Our atomistic simulations show that these changes in the hydrogen-bond network of water molecules cause the different rotational relaxation of water molecules between the two lipids.

    DOI: 10.1021/acs.langmuir.1c00417

  • Coarse-grained molecular dynamics simulations of void generation and growth processes in the fracture of the lamellar structure of polyethylene Reviewed

    Yuji Higuchi

    Physical Review E   103 ( 4 )   2021.4

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    DOI: 10.1103/physreve.103.042502

  • Cooperative roles of chemical reactions and mechanical friction in chemical mechanical polishing of gallium nitride assisted by OH radicals: tight-binding quantum chemical molecular dynamics simulations Reviewed

    Kentaro Kawaguchi, Yang Wang, Jingxiang Xu, Yusuke Ootani, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    Physical Chemistry Chemical Physics   23 ( 7 )   4075 - 4084   2021.1

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    <p>Chemical mechanical polishing (CMP) of Ga-face GaN is accelerated by the chemical reactions with OH radicals.</p>

    DOI: 10.1039/d0cp05826b

  • Generation of “Graphene Arch-Bridge” on a Diamond Surface by Si Doping: A First-Principles Computational Study Reviewed

    Bai, Sh, an, Xu, Jingxiang, Wang, Yang, Zhang, Qi, Tsuruda, Takeshi, Higuchi, Yuji, Ozawa, Nobuki, Adachi, Koshi, Martin, Jean Michel, Kubo, Momoji

    J. Phys. Chem. C   124 ( 48 )   26379 - 26386   2020.12

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    We reveal the generation of the "Graphene Arch-Bridge"on a diamond (111) surface by Si doping via first-principles calculations. The "Graphene Arch-Bridge"is different from a simple graphene structure because both its ends are pinned to the diamond surface, and it has an interesting arched-type curved structure. The large stress around the doped Si atom leads to the transition of the six-membered C ring to a five-membered C ring. The C atom excluded from the ring by this transition changes from an sp3 carbon to an sp2 carbon and generates the "Graphene Arch-Bridge"on the diamond (111) surface. These results suggest that the generation of the five-membered C ring by stress due to the Si doping is the reason why the "Graphene Arch-Bridge"is generated. Finally, we propose that the "Graphene Arch-Bridge"is the origin of the experimentally observed super-low friction of Si-doped diamond-like carbon (DLC). Furthermore, we suggest that the "Graphene Arch-Bridge"leads to the lower wear properties of Si-doped DLC compared with nondoped DLC because its ends of the bridge are pinned to the DLC surface.

    DOI: 10.1021/acs.jpcc.0c09716

  • Coarse-grained Molecular Dynamics Simulation of the Wear Mechanism of Cyclic Polymer Brushes Reviewed

    Liu, Zhongmin, Ootani, Yusuke, Uehara, Shuichi, Xu, Jingxiang, Wang, Yang, Miyazaki, Narumasa, Higuchi, Yuji, Ozawa, Nobuki, Kubo, Momoji

    Chemistry Letters   49 ( 10 )   1185 - 1188   2020.9

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    DOI: 10.1246/cl.200323

  • Supramolecular biocomposite hydrogels formed by cellulose and host-guest polymers assisted by calcium ion complexes Reviewed International journal

    Tsuchiya, Hinako, Sinawang, Garry, Asoh, Taka-aki, Osaki, Motofumi, Ikemoto, Yuka, Higuchi, Yuji, Yamaguchi, Hiroyasu, Harada, Akira, Uyama, Hiroshi, Takashima, Yoshinori

    Biomacromolecules   21 ( 9 )   3936 - 3944   2020.9

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    Hydrogels are biocompatible polymer networks; however, they have the disadvantage of having poor mechanical properties. Herein, the mechanical properties of host-guest hydrogels were increased by adding a filler and incorporating other noncovalent interactions. Cellulose was added as a filler to the hydrogels to afford a composite. Citric acid-modified cellulose (CAC) with many carboxyl groups was used instead of conventional cellulose. The preparation began with mixing an acrylamide-based αCD host polymer (p-αCD) and a dodecanoic acid guest polymer (p-AADA) to form supramolecular hydrogels (p-αCD/p-AADA). However, when CAC was directly added to p-αCD/p-AADA to form biocomposite hydrogels (p-αCD/p-AADA/CAC), it showed weaker mechanical properties than p-αCD/p-AADA itself. This was caused by the strong intramolecular hydrogen bonding (H-bonding) within the CAC, which prevented the CAC reinforcing p-αCD/p-AADA in p-αCD/p-AADA/CAC. Then, calcium chloride solution (CaCl2) was used to form calcium ion (Ca2+) complexes between the CAC and p-αCD/p-AADA. This approach successfully created supramolecular biocomposite hydrogels assisted by Ca2+ complexes (p-αCD/p-AADA/CAC/Ca2+) with improved mechanical properties relative to p-αCD/p-AADA hydrogels; the toughness was increased 6-fold, from 1 to 6 MJ/m3. The mechanical properties were improved because of the disruption of the intramolecular H-bonding within the CAC by Ca2+ and subsequent complex formation between the carboxyl groups of CAC and p-AADA. This mechanism is a new approach for improving the mechanical properties of hydrogels that can be broadly applied as biomaterials.

    DOI: 10.1021/acs.biomac.0c01095

  • Triboemission of hydrocarbon molecules from diamond-like carbon friction interface induces atomic-scale wear Reviewed

    Yang Wang, Naohiro Yamada, Jingxiang Xu, Jing Zhang, Qian Chen, Yusuke Ootani, Yuji Higuchi, Nobuki Ozawa, Maria-Isabel De Barros Bouchet, Jean Michel Martin, Shigeyuki Mori, Koshi Adachi, Momoji Kubo

    SCIENCE ADVANCES   5 ( 11 )   eaax9301   2019.11

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    Understanding atomic-scale wear is crucial to avoid device failure. Atomic-scale wear differs from macroscale wear because chemical reactions and interactions at the friction interface are dominant in atomic-scale tribological behaviors, instead of macroscale properties, such as material strength and hardness. It is particularly challenging to reveal interfacial reactions and atomic-scale wear mechanisms. Here, our operando friction experiments with hydrogenated diamond-like carbon ( DLC) in vacuum demonstrate the triboemission of various hydrocarbon molecules from the DLC friction interface, indicating its atomic-scale chemical wear. Furthermore, our reactive molecular dynamics simulations reveal that this triboemission of hydrocarbon molecules induces the atomic-scale mechanical wear of DLC. As the hydrogen concentration in hydrogenated DLC increases, the chemical wear increases while mechanical wear decreases, indicating an opposite effect of hydrogen concentration on chemical and mechanical wear. Consequently, the total wear shows a concave hydrogen concentration dependence, with an optimal hydrogen concentration for wear reduction of around 20%.

    DOI: 10.1126/sciadv.aax9301

  • Stress Transmitters at the Molecular Level in the Deformation and Fracture Processes of the Lamellar Structure of Polyethylene via Coarse-Grained Molecular Dynamics Simulations Reviewed

    Yuji Higuchi

    Macromolecules   52   6201 - 6212   2019.8

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    Stress Transmitters at the Molecular Level in the Deformation and Fracture Processes of the Lamellar Structure of Polyethylene via Coarse-Grained Molecular Dynamics Simulations

    DOI: 10.1021/acs.macromol.9b00636

  • Coarse-grained molecular dynamics simulation for uptake of nanoparticles into a charged lipid vesicle dominated by electrostatic interaction Reviewed

    Naofumi Shimokawa, Hiroaki Ito, Yuji Higuchi

    Phys. Rev. E   100   012407   2019.7

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    Coarse-grained molecular dynamics simulation for uptake of nanoparticles into a charged lipid vesicle dominated by electrostatic interaction

    DOI: 10.1103/PhysRevE.100.012407

  • Ionic Conductivity in Ionic Liquid Nano Thin Films Reviewed

    Maruyama Shingo, Prastiawan Ida, Bagus Hendra, Toyabe Kaho, Higuchi Yuji, Koganezawa Tomoyuki, Kubo Momoji, Matsumoto Yuji

    ACS Nano   12   10509 - 10517   2018.10

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    Ionic Conductivity in Ionic Liquid Nano Thin Films
    PMID: 30199622

    DOI: 10.1021/acsnano.8b06386

  • Molecular Interactions between Pentacene and Imidazolium Ionic Liquids: A Molecular Dynamics Study Reviewed

    Ida Bagus Hendra Prastiawan, Jingxiang Xu, Yusuke Ootani, Yuji Higuchi, Nobuki Ozawa, Shingo Maruyama, Yuji Matsumoto, Momoji Kubo

    Chemistry Letters   47 ( 9 )   1154 - 1157   2018.9

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    DOI: 10.1246/cl.180450

  • Tribochemical reactions and graphitization of diamond-like carbon against alumina give volcano-type temperature dependence of friction coefficients: A tight-binding quantum chemical molecular dynamics simulation Reviewed

    Yang Wang, Jingxiang Xu, Jing Zhang, Qian Chen, Yusuke Ootani, Yuji Higuchi, Nobuki Ozawa, Jean Michel Martin, Koshi Adachi, Momoji Kubo

    Carbon   133   350 - 357   2018.7

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    Diamond-like carbon (DLC) is a promising solid lubricant used as a protective coating to reduce friction against alumina. Friction properties of DLC/alumina are strongly affected by temperature. To improve the friction performance of DLC, we investigate the friction behaviors of DLC/alumina at various temperatures and reveal the mechanisms by using our tight-binding quantum chemical molecular dynamics method. We observe an interesting volcano-type temperature dependence of friction coefficients in our friction simulations. Friction coefficients of DLC/alumina are low and show little change at 300–600 K because no tribochemical reactions occur at the interface. However, as the temperature increases, friction coefficients increase at 600–800 K and subsequently decrease at 800–1000 K. At 600–800 K, interfacial C-O and C-Al bonds between two substrates are formed during friction, leading to a high friction coefficient. Interestingly, further increment of temperature to 800–1000 K induces the graphitization of DLC. The graphite-like surface suppresses the interfacial bond formation, reducing the friction coefficient. We reveal that the volcano-type temperature dependence of friction coefficients is due to the tribochemical reactions generating interfacial bonds at 600–800 K and the graphitization of DLC reducing the number of interfacial bonds at 800–1000 K.

    DOI: 10.1016/j.carbon.2018.03.034

  • First-principles calculation of activity and selectivity of the partial oxidation of ethylene glycol on Fe(0 0 1), Co(0 0 0 1), and Ni(1 1 1) Reviewed

    Nobuki Ozawa, Shigeki Chieda, Yuji Higuchi, Tatsuya Takeguchi, Miho Yamauchi, Momoji Kubo

    Journal of Catalysis   361   361 - 369   2018.5

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    First-principles calculation of activity and selectivity of the partial oxidation of ethylene glycol on Fe(0 0 1), Co(0 0 0 1), and Ni(1 1 1)
    To recycle ethylene glycol (HOCH2CH2OH) fuel in alkaline fuel cells, active and selective catalysts for partially oxidizing HOCH2CH2OH to glycolic acid (HOCH2COOH) and oxalic acid ((COOH)2) are required at the anode
    in other words, complete oxidation of HOCH2CH2OH to CO2 prevents ethylene glycol recycling. We investigate catalyst activity and selectivity for oxidizing HOCH2CH2OH to HOCH2COOH on Fe(0 0 1), Co(0 001), and Ni(1 1 1) via first-principles calculations. We calculate the oxidation reaction path from HOCH2CH2OH to HOCH2COOH without C–C bond dissociation to avoid CO2 generation. Partial oxidation of HOCH2CH2OH to HOCH2COOH without C–C bond dissociation proceeds as follows: O–H bond dissociation of HOCH2CH2OH to generate HOCH2CH2O
    C–H bond dissociation of HOCH2CH2O to generate HOCH2CHO
    C–H bond dissociation of HOCH2CHO to generate HOCH2CO
    and OH addition to HOCH2CO to generate HOCH2COOH. The activation energies for O–H bond dissociation of HOCH2CH2OH and C–H bond dissociation of HOCH2CH2O and HOCH2CHO on Fe(0 0 1) are 20.2, 22.8, and 35.2 kcal/mol, respectively, which are the lowest of the three surfaces. Thus, Fe(0 0 1) is most active. To determine the selectivity, we compare the bond dissociation activation energies. The activation energies for C–C bond dissociation of HOCH2CH2OH and HOCH2CH2O on Fe(0 0 1) (66.7 and 39.5 kcal/mol, respectively) are higher than those for O–H bond dissociation of HOCH2CH2OH (20.2 kcal/mol) and C–H bond dissociation of HOCH2CH2O (22.8 kcal/mol), implying that the O–H bond of HOCH2CH2OH and C–H bond of HOCH2CH2O dissociate before the C–C bond dissociation during oxidation on Fe(0 0 1). In contrast, the activation energies for C–H and C–C bond dissociation of HOCH2CHO (35.2 and 32.8 kcal/mol, respectively) are similar. The C–H and C–C bonds therefore dissociate during HOCH2CHO oxidation. On Co(0 0 0 1) and Ni(1 1 1), the activation energies for C–C bond dissociation of HOCH2CH2O and HOCH2CHO are lower than those for their C–H bond dissociation. Therefore, Fe(0 0 1) is more active and selective than Co(0 0 0 1) and Ni(1 1 1) for the partial oxidation of HOCH2CH2OH to HOCH2COOH.

    DOI: 10.1016/j.jcat.2018.03.017

  • Fracture processes of crystalline polymers using coarse-grained molecular dynamics simulations Reviewed

    Yuji Higuchi

    Polymer Journal   50   1 - 10   2018.5

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    Molecular simulations are powerful tools for revealing the properties of polymers at the molecular level. In particular, coarse-grained molecular dynamics simulations are useful for elucidating the deformation and fracture processes of polymers. However, in the case of crystalline polymers, it is difficult to reproduce experimentally observed structures and mechanical properties using these models. This review describes our recent investigations into the deformation and fracture processes of crystalline polymers using coarse-grained molecular dynamics simulations. We were able to successfully reproduce the lamellar structure of polyethylene, which is a fundamental structural feature of this polymer, and obtain a stress–strain curve that exhibited good consistency with that observed experimentally. The molecular dynamics simulations revealed that void generation in the amorphous layers was caused by the movement of the chain ends, which is difficult to observe through experiments. The conditions required to reproduce the experimentally observed structure and mechanical properties using molecular simulations are also discussed.

    DOI: 10.1038/s41428-018-0067-1

  • Fracture Process of Double-Network Gels by Coarse-Grained Molecular Dynamics Simulation Reviewed

    Yuji Higuchi, Keisuke Saito, Takamasa Sakai, Jian Ping Gong, Momoji Kubo

    MACROMOLECULES   51 ( 8 )   3075 - 3087   2018.4

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    Double-network (DN) gels consisting of highly and slightly cross linked networks exhibit good mechanical properties, complicated deformation behavior, and fracture processes owing to the existence of a large number of influential parameters. To determine the effects of these factors at the molecular level to improve the mechanical properties further, we studied the fracture processes of DN gels using a coarse-grained molecular dynamics simulation. First, we propose a modeling method for DN gels consisting of highly (first) and slightly (second) cross-linked networks. Then, we stretch the DN gels and investigate the effects of the network ratio, chain length, and first- and second-network structures on the mechanical properties. During the stretching, the stress increases with the bond breaking in the first network. Then, the stress further increases with the simultaneous bond breaking in the first and second networks when they are entangled with one another. Finally, the bond breaking in the first network stops, and only the bond breaking in the second network occurs. The second network remains at a high strain, which prevents rupture of the gel. We find that (i) a low concentration of the first network is necessary for the gel to exhibit the properties of both the first and second networks, (ii) a tense first network increases the Young's modulus, and (iii) the second network with a long chain length and separated cross linking points increases the peak stress and ductility. We have therefore successfully elucidated the effects of the network structures on the mechanical properties of DN gels.

    DOI: 10.1021/acs.macromol.8b00124

  • Tight-Binding Quantum Chemical Molecular Dynamics Study on the Friction and Wear Processes of Diamond-Like Carbon Coatings: Effect of Tensile Stress Reviewed

    Yang Wang, Jingxiang Xu, Yusuke Ootani, Shandan Bai, Yuji Higuchi, Nobuki Ozawa, Koshi Adachi, Jean Michel Martin, Momoji Kubo

    ACS APPLIED MATERIALS & INTERFACES   9 ( 39 )   34396 - 34404   2017.10

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    Diamond-like carbon (DLC) coatings have attracted much attention as an excellent solid lubricant due to their low-friction properties. However, wear is still a problem for the durability of DLC coatings. Tensile stress on the surface of DLC coatings has an important effect on the wear behavior during friction. To improve the tribological properties of DLC coatings, we investigate the friction process and wear mechanism under various tensile stresses by using our tight-binding quantum chemical molecular dynamics method. We observe the formation of C-C bonds between two DLC substrates under high tensile stress during friction, leading to a high friction coefficient. Furthermore, under high tensile stress, C-C bond dissociation in the DLC substrates is observed during friction, indicating the atomic-level wear. These dissociations of C-C bonds are caused by the transfer of surface hydrogen atoms during friction. This work provides atomic-scale insights into the friction process and the wear mechanism of DLC coatings during friction under tensile stress.

    DOI: 10.1021/acsami.7b07551

  • Parallel Large-Scale Molecular Dynamics Simulation Opens New Perspective to Clarify the Effect of a Porous Structure on the Sintering Process of Ni/YSZ Multiparticles Reviewed

    Jingxiang Xu, Yuji Higuchi, Nobuki Ozawa, Kazuhisa Sato, Toshiyuki Hashida, Momoji Kubo

    ACS APPLIED MATERIALS & INTERFACES   9 ( 37 )   31816 - 31824   2017.9

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    Ni sintering in the Ni/YSZ porous anode of a solid oxide fuel cell changes the porous structure, leading to degradation. Preventing sintering and degradation during operation is a great challenge. Usually, a sintering molecular dynamics (MD) simulation model consisting of two particles on a substrate is used; however, the model cannot reflect the porous structure effect on sintering. In our previous study, a multi-nanoparticle sintering modeling method with tens of thousands of atoms revealed the effect of the particle framework and porosity on sintering. However, the method cannot reveal the effect of the particle size on sintering and the effect of sintering on the change in the porous structure. In the present study, we report a strategy to reveal them in the porous structure by using our multi-nanoparticle modeling method and a parallel large-scale multimillion-atom MD simulator. We used this method to investigate the effect of YSZ particle size and tortuosity on sintering and degradation in the Ni/YSZ anodes. Our parallel large-scale MD simulation showed that the sintering degree decreased as the YSZ particle size decreased. The gas fuel diffusion path, which reflects the overpotential, was blocked by pore coalescence during sintering. The degradation of gas diffusion performance increased as the YSZ particle size increased. Furthermore, the gas diffusion performance was quantified by a tortuosity parameter and an optimal YSZ particle size, which is equal to that of Ni, was found for good diffusion after sintering. These findings cannot be obtained by previous MD sintering studies with tens of thousands of atoms. The present parallel large-scale multimillion-atom MD simulation makes it possible to clarify the effects of the particle size and tortuosity on sintering and degradation.

    DOI: 10.1021/acsami.7b07737

  • Deformation and Fracture Processes of a Lamellar Structure in Polyethylene at the Molecular Level by a Coarse-Grained Molecular Dynamics Simulation Reviewed

    Yuji Higuchi, Momoji Kubo

    MACROMOLECULES   50 ( 9 )   3690 - 3702   2017.5

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    Coarse-grained molecular dynamics simulations can model the deformation and fracture processes of the lamellar structure in polyethylene on a molecular scale; however, the simulations have not been performed due to the difficulty in building the structure and the limitations of small-scale simulations on the order of 104 beads. Thus, we propose a crystallization method for a large-scale lamellar structure on the order of 106 beads. The highly oriented lamellar structure is stretched in a coarse-grained molecular dynamics simulation. The stress and variation of crystallinity during stretching parallel and perpendicular to the crystal direction agree with experimental results, confirming the validity of our simulation results. During stretching parallel to the crystal direction, the amorphous layers crystallize and the crystalline layers fragment. We also find that the movement of the polymer chain ends from amorphous to crystalline layers, which is difficult to observe experimentally, increases the compression and generation of voids in the amorphous layers.

    DOI: 10.1021/acs.macromol.6b02613

  • Diamond-like carbon coating under oleic acid lubrication: Evidence for graphene oxide formation in superlow friction Reviewed

    Maria Isabel De Barros Bouchet, Jean Michel Martin, Jose Avila, Makoto Kano, Kentaro Yoshida, Takeshi Tsuruda, Shandan Bai, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo, Maria C. Asensio

    SCIENTIFIC REPORTS   7   2017.4

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    The achievement of the superlubricity regime, with a friction coefficient below 0.01, is the Holy Grail of many tribological applications, with the potential to have a remarkable impact on economic and environmental issues. Based on a combined high-resolution photoemission and soft X-ray absorption study, we report that superlubricity can be realized for engineering applications in bearing steel coated with ultra-smooth tetrahedral amorphous carbon (ta-C) under oleic acid lubrication. The results show that tribochemical reactions promoted by the oil lubrication generate strong structural changes in the carbon hybridization of the ta-C hydrogen-free carbon, with initially high sp(3) content. Interestingly, the macroscopic superlow friction regime of moving mechanical assemblies coated with ta-C can be attributed to a few partially oxidized graphene-like sheets, with a thickness of not more than 1 nm, formed at the surface inside the wear scar. The sp(2) planar carbon and oxygen-derived species are the hallmark of these mesoscopic surface structures created on top of colliding asperities as a result of the tribochemical reactions induced by the oleic acid lubrication. Atomistic simulations elucidate the tribo-formation of such graphene-like structures, providing the link between the overall atomistic mechanism and the macroscopic experimental observations of green superlubricity in the investigated ta-C/oleic acid tribological systems.

    DOI: 10.1038/srep46394

  • Effect of Polarity of a Substrate on ZnO Crystal Growth Process by Molecular Dynamics Simulation Reviewed

    Shunsuke KAWAGISHI, Jingxiang XU, Yusuke OOTANI, Takeshi NISHIMATSU, Yuji HIGUCHI, Nobuki OZAWA, Momoji KUBO

    Journal of Computer Chemistry, Japan   15 ( 6 )   244 - 245   2017.2

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    Effect of Polarity of a Substrate on ZnO Crystal Growth Process by Molecular Dynamics Simulation

    DOI: 10.2477/jccj.2016-0056

  • Computational Study on Low Friction Mechanism of Diamond-like Carbon Induced by Oxidation Reaction Reviewed

    Shandan Bai, Jingxiang Xu, Yuji Higuchi, Nobuki Ozawa, Koshi Adachi, Shigeyuki Mori, Kazue Kurihara, Momoji Kubo

    2016 IEEE 16TH INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO)   941 - 943   2016.11

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    Water lubrication has been attracting attention for environment-friendly society due to low CO2 emission. Furthermore, carbon-based materials such as diamond-like carbon (DLC) show the low friction properties in water lubrication due to the oxidation reaction on the surface in pre-sliding. However, the influence of oxidation reactions on low friction mechanism is still unclear. In this study, we clarify the structure change of DLC with the oxidation reaction in the pre-sliding using first-principles calculation, which suggests the low friction mechanism of DLC in water lubrication. The results show the structure change from sp(3) carbon (Csp(3)) to sp(2) carbon (Csp(2)) by the oxidation reaction on the surface. Furthermore, the Csp(2) rich surface in water lubrication indicates the smooth sliding. We suggest that the structure change from Csp(3) to Csp(2) would affect low friction properties of DLC in water lubrication.

  • Theoretical Study on Sintering of Ni Nanoparticles in the Anode of Solid Oxide Fuel Cell under Water Vapor Environment Reviewed

    Jingxiang Xu, Shandan Bai, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    2016 IEEE 16TH INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO)   884 - 887   2016.11

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    Sintering of Ni particles in the Ni-based anode is a major obstacle to the widespread use of solid oxide fuel cell because the sintering induces the degradation in the anode. The large amount of water vapor in the fuel is known to accelerate the degradation during the operation. However, the detailed accelerated sintering mechanism is unclear. In this study, to clear the accelerated sintering mechanism during the initial stage of the sintering by water vapor, we investigated the adsorption and dissociation of water molecules on the Ni surface as well as the effect of the terminations of O, H, and OH on the interaction between the Ni clusters by density functional theory because the sintering of Ni particles is started by the Ni particles approaching each other due to the attractive interaction between Ni particles at the initial stage. In our adsorption and dissociation calculations, increasing the amount of water vapor facilitates the adsorption of H2O molecule on the Ni surface due to the H-bond interaction. Meanwhile, the activation energy for the dissociation of H2O molecules on the Ni surface is also lowered with increasing the amount of H2O molecules. Then, we calculated the interaction between Ni cluster, and O terminated, OH terminated, and H terminated Ni clusters. We observed that the attractive interaction between Ni cluster and O terminated Ni cluster is larger than that between two Ni clusters in vacuum. Enhancing the attractive interaction is not observed in the H terminated and OH terminated Ni clusters. It indicates that two Ni clusters approaching each other is faster under the water vapor environment than that in vacuum due to the strong attractive interaction caused by the termination of O. Thus, we suggest that the generation of O termination plays an important role in the sintering at the initial stage under the water vapor environment.

  • Coarse-grained molecular dynamics simulation of binary charged lipid membranes: Phase separation and morphological dynamics Reviewed

    Hiroaki Ito, Yuji Higuchi, Naofumi Shimokawa

    PHYSICAL REVIEW E   94 ( 4 )   2016.10

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    Biomembranes, which are mainly composed of neutral and charged lipids, exhibit a large variety of functional structures and dynamics. Here, we report a coarse-grained molecular dynamics (MD) simulation of the phase separation and morphological dynamics in charged lipid bilayer vesicles. The screened long-range electrostatic repulsion among charged head groups delays or inhibits the lateral phase separation in charged vesicles compared with neutral vesicles, suggesting the transition of the phase-separationmechanism from spinodal decomposition to nucleation or homogeneous dispersion. Moreover, the electrostatic repulsion causes morphological changes, such as pore formation, and further transformations into disk, string, and bicelle structures, which are spatiotemporally coupled to the lateral segregation of charged lipids. Based on our coarse-grained MD simulation, we propose a plausible mechanism of pore formation at the molecular level. The pore formation in a charged-lipid-rich domain is initiated by the prior disturbance of the local molecular orientation in the domain.

    DOI: 10.1103/PhysRevE.94.042611

  • Coarse-grained molecular dynamics simulation of the void growth process in the block structure of semicrystalline polymers Reviewed

    Yuji Higuchi, Momoji Kubo

    MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING   24 ( 5 )   2016.6

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    We study fracture processes of amorphous and semicrystalline polymers with a coarse-grained molecular dynamics simulation. In the amorphous state, the stress caused by strain mainly arises from the loss of the attractive interaction in the voids. However, in semicrystalline polymers, the elongation of bonding is the dominant factor and it causes much more stress than that in an amorphous state. This is because growth of the voids is prevented by the amorphous regions and it is difficult to relax the folded polymers.

    DOI: 10.1088/0965-0393/24/5/055006

  • MPI並列による大規模粗視化分子動力学シミュレーション: 分子スケールにおける高分子材料の機械的特性の解明 Reviewed

    樋口 祐次, 久保 百司

    HPCS2016論文集   2016.6

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    Large-scale coarse-grained molecular dynamics simulation based on MPI parallel computing: Mechanical property of polymers in molecular scale

  • Atomistic Mechanisms of Chemical Mechanical Polishing of a Cu Surface in Aqueous H2O2: Tight-Binding Quantum Chemical Molecular Dynamics Simulations Reviewed

    Kentaro Kawaguchi, Hiroshi Ito, Takuya Kuwahara, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    ACS APPLIED MATERIALS & INTERFACES   8 ( 18 )   11830 - 11841   2016.5

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    We applied our original chemical mechanical polishing (CMP) simulator based on the tight-binding quantum chemical molecular dynamics (TB-QCMD) method to clarify the atomistic mechanism of CMP processes on a Cu(111) surface polished with a SiO2 abrasive grain in aqueous H2O2. We reveal that the oxidation of the Cu(111) surface mechanically induced at the friction interface is a key process in CMP. In aqueous H2O2, in the first step, OH groups and O atoms adsorbed on a nascent Cu surface are generated by the chemical reactions of H2O2 molecules. In the second step, at the friction interface between the Cu surface and the abrasive grain, the surface-adsorbed O atom intrudes into the Cu bulk and dissociates the Cu Cu bonds. The dissociation of the Cu Cu back bonds raises a Cu atom from the surface that is mechanically sheared by the abrasive grain. In the third step, the raised Cu atom bound to the surface-adsorbed OH groups is removed from the surface by the generation and desorption of a Cu(OH)(2) molecule. In contrast, in pure water, there are no geometrical changes in the Cu surface because the H2O molecules do not react with the Cu surface, and the abrasive grain slides smoothly on the planar Cu surface. The comparison between the CMP simulations in aqueous H2O2 and pure water indicates that the intrusion of a surface-adsorbed O atom into the Cu bulk is the most important process for the efficient polishing of the Cu surface because it induces the dissociation of the Cu Cu bonds and generates raised Cu atoms that are sheared off by the abrasive grain. Furthermore, density functional theory calculations show that the intrusion of the surface-adsorbed O atoms into the Cu bulk has a high activation energy of 28.2 kcal/mol, which is difficult to overcome at 300 K. Thus, we suggest that the intrusion of surface-adsorbed O atoms into the Cu bulk induced by abrasive grains at the friction interface is a rate-determining step in the Cu CMP process.

    DOI: 10.1021/acsami.5b11910

  • Tight-binding quantum chemical molecular dynamics simulations for the elucidation of chemical reaction dynamics in SiC etching with SF6/O-2 plasma Reviewed

    Hiroshi Ito, Takuya Kuwahara, Kentaro Kawaguchi, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   18 ( 11 )   7808 - 7819   2016.3

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    We used our etching simulator [H. Ito et al., J. Phys. Chem. C, 2014, 118, 21580-21588] based on tight-binding quantum chemical molecular dynamics (TB-QCMD) to elucidate SiC etching mechanisms. First, the SiC surface is irradiated with SF5 radicals, which are the dominant etchant species in experiments, with the irradiation energy of 300 eV. After SF5 radicals bombard the SiC surface, Si-C bonds dissociate, generating Si-F, C-F, Si-S, and C-S bonds. Then, etching products, such as SiS, CS, SiFx, and CFx (x = 1-4) molecules, are generated and evaporated. In particular, SiFx is the main generated species, and Si atoms are more likely to vaporize than C atoms. The remaining C atoms on SiC generate C-C bonds that may decrease the etching rate. Interestingly, far fewer Si-Si bonds than C-C bonds are generated. We also simulated SiC etching with SF3 radicals. Although the chemical reaction dynamics are similar to etching with SF5 radicals, the etching rate is lower. Next, to clarify the effect of O atom addition on the etching mechanism, we also simulated SiC etching with SF5 and O radicals/atoms. After bombardment with SF5 radicals, Si-C bonds dissociate in a similar way to the etching without O atoms. In addition, O atoms generate many C-O bonds and COy (y = 1-2) molecules, inhibiting the generation of C-C bonds. This indicates that O atom addition improves the removal of C atoms from SiC. However, for a high O concentration, many C-C and Si-Si bonds are generated. When the O atoms dissociate the Si-C bonds and generate dangling bonds, the O atoms terminate only one or two dangling bonds. Moreover, at high O concentrations there are fewer S and F atoms to terminate the dangling bonds than at low O concentration. Therefore, few dangling bonds of dissociated Si and C atoms are terminated, and they form many Si-Si and C-C bonds. Furthermore, we propose that the optimal O concentration is 50-60% because both Si and C atoms generate many etching products producing fewer C-C and Si-Si bonds are generated. Finally, we conclude that our TB-QCMD etching simulator is effective for designing the optimal conditions for etching processes in which chemical reactions play a significant role.

    DOI: 10.1039/c5cp06515a

  • Origin of Chemical Order in a-SixCyHz: Density-Functional Tight-Binding Molecular Dynamics and Statistical Thermodynamics Calculations Reviewed

    Takuya Kuwahara, Hiroshi Ito, Kentaro Kawaguchi, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    JOURNAL OF PHYSICAL CHEMISTRY C   120 ( 5 )   2615 - 2627   2016.2

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    We investigate the growth mechanisms and structures of hydrogenated amorphous silicon carbide (a-SixCyHz during chemical vapor deposition (CVD) by using density-functional tight-binding molecular dynamics (DFTB MD) and statistical thermodynamics (ST) calculations. Our multiscale modeling from an atomic to an experimental scale allows us to bridge the gap between micro- and macroscopic knowledge. As in any compound, the degree of chemical order in a-SixCyHz is of practical importance. However, the origin of chemical order and effects of composition on the degree of chemical order remain unknown. First, CVD simulations are performed by the impingement of CH3 and SiH3 radicals on a Si(001)-(2 X 1):H surface with DFTB MD. The initial growth process consists of an abstraction-adsorption mechanism, where a CH3 or SiH3 radical abstracts a H atom and forms a dangling bond (DB) on the surface, and a subsequent CH3 or SiH3 radical is adsorbed on the DB. A surface-adsorbed CH2 species with a DB is inserted into a neighboring Si-Si bond converting it to a Si-C bond. The bond rearrangement simultaneously transfers the DB from the C to Si atoms. A CH3 radical is then adsorbed on the Si atom, forming a Si-C bond. The absence of DBs on C atoms reduces the opportunity for forming C-C bonds. Therefore, the bond-rearrangement and DB transfer mechanism explain why Si C bonds are preferentially formed instead of Si-Si and C-C bonds. Second, to model CVD growth of a-SixCyHz on a macroscopic scale, we develop a ST model for a-SixCyHz, calculating the bonding fractions. Importantly, we show that the degree of chemical order depends on the H atom fraction. The bonding fractions obtained by ST results show excellent agreement with those obtained by DFTB MD calculations. Our DFTB MD and ST models predict the relationship between the composition and the degree of chemical order, and bridge a gap between micro- and macroscopic observations. The models can be used for designing materials for other covalent and ionic compounds at micro- to macroscales.

    DOI: 10.1021/acs.jpcc.5b08561

  • Coupling between pore formation and phase separation in charged lipid membranes Reviewed

    Hiroki Himeno, Hiroaki Ito, Yuji Higuchi, Tsutomu Hamada, Naofumi Shimokawa, Masahiro Takagi

    PHYSICAL REVIEW E   92 ( 6 )   2015.12

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    We investigated the effect of charge on the membrane morphology of giant unilamellar vesicles (GUVs) composed of various mixtures containing charged lipids. We observed the membrane morphologies by fluorescent and confocal laser microscopy in lipid mixtures consisting of a neutral unsaturated lipid [dioleoylphosphatidylcholine (DOPC)], a neutral saturated lipid [dipalmitoylphosphatidylcholine (DPPC)], a charged unsaturated lipid [dioleoylphosphatidylglycerol (DOPG((-)))], a charged saturated lipid [dipalmitoylphosphatidylglycerol (DPPG((-)))], and cholesterol (Chol). In binary mixtures of neutral DOPC-DPPC and charged DOPC-DPPG((-)), spherical vesicles were formed. On the other hand, pore formation was often observed with GUVs consisting of DOPG((-)) and DPPC. In a DPPC-DPPG((-)-)Chol ternary mixture, pore-formed vesicles were also frequently observed. The percentage of pore-formed vesicles increased with the DPPG((-)) concentration. Moreover, when the head group charges of charged lipids were screened by the addition of salt, pore-formed vesicles were suppressed in both the binary and ternary charged lipid mixtures. We discuss the mechanisms of pore formation in charged lipid mixtures and the relationship between phase separation and the membrane morphology. Finally, we reproduce the results seen in experimental systems by using coarse-grained molecular dynamics simulations.

    DOI: 10.1103/PhysRevE.92.062713

  • Development and application of a double-network gel modeling method for fracture processes using a coarse-grained molecular dynamics simulation Reviewed

    Saito Keisuke, Higuchi Yuji, Ozawa Nobuki, Kubo Momoji

    Journal of Computer Chemistry, Japan   14 ( 3 )   94 - 95   2015.10

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    Development and application of a double-network gel modeling method for fracture processes using a coarse-grained molecular dynamics simulation
    We examine the mechanism of fracture processes in a double-network (DN) gel model by using a coarse-grained molecular dynamics simulation. Initially, we develop a modeling method for DN gel containing both slightly and highly cross-linked networks, and then stretch the DN gel model. During stretching, the highly cross-linked network begins to dissociate at a strain of 1.0, increasing the stress. At strains from 4.0 to 5.0, the slightly and highly cross-linked networks simultaneously dissociate and the stress decreases. Then, the dissociation of the highly cross-linked network stops and only the slightly cross-linked network dissociates at a strain of 12.0, while the stress remains almost the same. We reveal that characteristics of each type of network gradually appear in the DN gel. Next, we change the polymer chain length to reveal its influence on the mechanical properties of the gel. An increase in the length of the slightly cross-linked network chains improves the strength of the DN gel, whereas that of the highly cross-linked network chains does not affect its strength. An increase in the slightly cross-linked network chain length increases the number of entanglements, leading to the increase in strength.

    DOI: 10.2477/jccj.2015-0053

  • Different dynamic behaviors of the dissociation and recombination reactions in a model calculation of polyethylene by first-principles steered molecular dynamics simulation Reviewed

    Yuji Higuchi, Takeshi Ishikawa, Nobuki Ozawa, Laurent Chazeau, Jean-Yves Cavaille, Momoji Kubo

    CHEMICAL PHYSICS   459   96 - 101   2015.9

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    We investigate the different dynamics of the stress-induced dissociation and recombination reactions in a model of polyethylene by a first-principles molecular dynamics simulation at the B3LYP/6-31g(d) level. The dissociation under external forces acting on the chemical reaction site at 300 K follows the same pathway as the one calculated by the static first-principles method because it has a similar activation barrier to that of the static first-principles calculation. On the other hand, in the recombination process, thermal fluctuations causes collisions between hydrogen atoms at the chain ends. Furthermore, when external forces do not directly act on the chemical reaction site, two different dissociation processes are observed. On the other hand, recombination process is not observed due to rarely contact of the radical carbon. These results indicate that dissociation and recombination dynamics are very different, showing the importance of the dynamic calculation. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.chemphys.2015.08.007

  • Multi-nanoparticle model simulations of the porosity effect on sintering processes in Ni/YSZ and Ni/ScSZ by the molecular dynamics method

    Jingxiang Xu, Shandan Bai, Yuji Higuchi, Nobuki Ozawa, Kazuhisa Sato, Toshiyuki Hashida, Momoji Kubo

    Journal of Materials Chemistry A   3 ( 43 )   21518 - 21527   2015.9

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    <p>The effects of the ceramic type and porosity on the sintering and degradation in Ni/YSZ and Ni/ScSZ anodes are unveiled by a recently developed multi-nanoparticle sintering simulation method based on molecular dynamics simulation.</p>

    DOI: 10.1039/c5ta05575j

  • Tribocatalytic Reaction of Polytetrafluoroethylene Sliding on an Aluminum Surface Reviewed

    Tasuku Onodera, Kenji Kawasaki, Takayuki Nakakawaji, Yuji Higuchi, Nobuki Ozawa, Kazue Kurihara, Momoji Kubo

    JOURNAL OF PHYSICAL CHEMISTRY C   119 ( 28 )   15954 - 15962   2015.7

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    To improve the tribological performance of polytetrafluoroethylene (PTFE) resin sliding against a metallic surface, it is important to understand the chemical behavior of PTFE in this sliding system. The tribochemical reaction of PTFE on an aluminum surface has been strenuously studied by a series of computational chemistry methods [Onodera, T., et al. J. Phys. Chem. C 2014, 118, 5390-5396, and Onodera, T., et al. J. Phys. Chem. C 2014, 118, 11820-11826]. One of the most important insights was that PTFE reacted tribochemically with the oxidized surface of aluminum as a Lewis acid catalyst, forming a fluoride on the aluminum surface. The aluminum fluoride formed was a cause of decreasing tribological performance of PTFE because of less formation of a transfer film. In regard to this tribochemical reaction, it was suggested that preventing the fluoride formation is a key to improving the tribological performance of PTFE sliding against an aluminum surface. In this study, to investigate fluoride formation by a tribochemical reaction, the catalytic effect Of an oxidized aluminum surface was investigated experimentally and theoretically. Two phases of an oxidized aluminum surface, namely, the alpha and gamma phases of alumina, were chosen for investigating the catalytic tribochemistry of PTFE. A thermogravimetric analysis showed that the gamma-alumina surface potentially exhibited a stronger catalytic effect in regard to PTFE since the reaction took place at lower temperature. The effect of the catalytic reaction on the tribological performance of PTFE was then investigated by a pin-on-disk tribometer. The results of this investigation show that the amount of wear of PTFE on the gamma-alumina surface was higher than that on the a-alumina surface. By observing the wear scar on alumina surfaces by a scanning electron microscope (SEM) combined with energy-dispersive X-ray spectroscopy (EDX), it was clarified that the transfer film formed on the gamma-alumina surface was less abundant, while it was regularly formed and more abundant on the a-alumina surface. In other words, the antiwear performance of PTFE was decreased because a lower amount of transfer film was formed by the catalytic effect during friction. In addition, a density-functional-theory (DFT) calculation also showed a stronger catalytic effect on the gamma-alumina surface because the energy barrier for the chemical reaction producing fluoride was lower than that on the a-alumina surface. On the basis of these results, it was suggested that controlling the catalytic reaction of PTFE on the sliding surface is one of the ways to improve the antiwear performance of PTFE.

    DOI: 10.1021/acs.jpcc.5b01370

  • Density functional theory study of dopant effect on sintering in the anode of solid oxide fuel cell Reviewed

    Jingxiang Xu, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    ECS Transactions   68 ( 1 )   3187 - 3193   2015.6

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    Sintering of Ni particles in the Ni/Y-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    anode is a major obstacle to the widespread use of solid oxide fuel cell. In this study, we investigated the dopant effect on the diffusion of a Ni atom on the ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface with dopants (Y and Al) by density functional theory calculations in order to inhibit the sintering. The most stable adsorption sites of the Ni atom on the Al-doped and Y-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surfaces are the vicinity of the twofold-coordination oxygen atom and the vicinity of an oxygen vacancy, respectively. It is found that the most stable adsorption energy on the Al-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface is larger than that on the Y-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface. The analysis of diffusion path based on the potential energy surfaces of the Ni atom on the two surfaces shows that the energy barrier for the diffusion of the Ni atom on the Al-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface is larger than that on the Y-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface. The diffusion of the Ni atom on the Al-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface is more difficult than that on the Y-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface. This is because the Ni atom strongly bound to the twofold-coordination oxygen atom and the Ni atom is constrained in the Al-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface. Thus, the Ni sintering on the Al-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface is inhibited compared to that on the Y-doped ZrO&lt
    inf&gt
    2&lt
    /inf&gt
    surface.

    DOI: 10.1149/06801.3187ecst

  • The reason why thin-film silicon grows layer by layer in plasma-enhanced chemical vapor deposition Reviewed

    Takuya Kuwahara, Hiroshi Ito, Kentaro Kawaguchi, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    SCIENTIFIC REPORTS   5   2015.3

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    Thin-film Si grows layer by layer on Si(001)-(2x1):H in plasma-enhanced chemical vapor deposition. Here we investigate the reason why this occurs by using quantum chemical molecular dynamics and density functional theory calculations. We propose a dangling bond (DB) diffusion model as an alternative to the SiH3 diffusion model, which is in conflict with first-principles calculation results and does not match the experimental evidence. In our model, DBs diffuse rapidly along an upper layer consisting of Si-H-3 sites, and then migrate from the upper layer to a lower layer consisting of Si-H sites. The subsequently incident SiH3 radical is then adsorbed onto the DB in the lower layer, producing two-dimensional growth. We find that DB diffusion appears analogous to H diffusion and can explain the reason why the layer-by-layer growth occurs.

    DOI: 10.1038/srep09052

  • Chemical Mechanical Properties of Perovskite Oxide Abrasive Grain: First-Principles Approach Reviewed

    Nobuki Ozawa, Yuji Higuchi, Momoji Kubo

    2014 INTERNATIONAL CONFERENCE ON PLANARIZATION/CMP TECHNOLOGY (ICPT)   203 - 204   2014.11

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    To elucidate the chemical mechanical polishing (CMP) performance of perovskite oxide abrasive grain for glass, we investigated electronic states of CaZrO3 and SrFeO3 by the first-principles calculation. The calculation results show that the Zr and Fe atoms in CaZrO3 and SrFeO3 take low valence states. We suggest that the metal atoms in perovskite oxide are effective for the glass polishing since low-valent metal atoms can weaken the Si-O bond of the glass surface by electron donation based on our reported CMP mechanism of glass by CeO2 abrasive grains.

  • Chemical Mechanical Polishing Mechanisms for Gallium Nitride: Quantum Chemical Molecular Dynamics Simulations Reviewed

    Kentaro Kawaguchi, Takehiro Aizawa, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    2014 INTERNATIONAL CONFERENCE ON PLANARIZATION/CMP TECHNOLOGY (ICPT)   39 - 41   2014.11

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    We developed a chemical mechanical polishing (CMP) simulator based on tight-binding quantum chemical molecular dynamics method and applied it to gallium nitride (GaN) CMP process. We successfully clarified the chemical reaction dynamics at the friction interface between the GaN substrate and an abrasive grain in pure water; surface-adsorbed H2O molecules, OH groups, and H atoms are generated by the adsorption and dissociation of water on the GaN surface. Our developed CMP simulator is capable of predicting the CMP processes controlled by chemical reactions.

  • Tight-Binding Quantum Chemical Molecular Dynamics Simulations of Mechanisms of SiO2 Etching Processes for CF2 and CF3 Radicals Reviewed

    Hiroshi Ito, Takuya Kuwahara, Kentaro Kawaguchi, Yuji Higuchi, Nobuki Ozawa, Seiji Samukawa, Momoji Kubo

    JOURNAL OF PHYSICAL CHEMISTRY C   118 ( 37 )   21580 - 21588   2014.9

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    The plasma etching of SiO2 by CF2 and CF3 radicals is investigated by using our etching simulator based on tight-binding quantum chemical molecular dynamics method. During etching simulations, C-F and Si-O bonds dissociate and C-O and Si F bonds are generated. Moreover, CO, CO2, COF, and COF2 molecules form, which is consistent with previous experimental studies. We also examine the dependence of the etching mechanism of CF2 and CF3 radicals on the kinetic energy of irradiation. At a low kinetic energy of 10 eV, a CF2 radical dissociates more Si-O bonds than a CF3 radical does. This is because the high chemical reactivity of the CF2 diradical accelerates the etching process. At a high kinetic energy of 150 eV, a CF3 radical dissociates more Si-O bonds than a CF2 radical does. This is because a CF3 radical generates a greater number of reactive F atoms than a CF2 radical does and thus forms more Si-F bonds. Thus, we conclude that our etching simulator modeled the different SiO2 etching mechanisms of CF2 and CF3 radicals, which arose from the different chemical reactivities of radicals and F atoms at different kinetic energies. This is the first quantum chemistry study to model complicated chemical reactions, which are induced by the attack of many radical species, and clarify the different SiO2 etching mechanisms for CF2 and CF3 radicals.

    DOI: 10.1021/jp5015252

  • Tribo-Chemical Reaction of Molybdenum Dithiocarbamate on Diamond-Like Carbon Films: Quantum Chemical Molecular Dynamics Simulation Reviewed

    Murabayashi Hiroki, Tsuruda Takeshi, Wang Yang, Kobayashi Yoshihiko, Bai Shandan, Higuchi Yuji, Ozawa Nobuki, Adachi Koshi, Kubo Momoji

    Journal of Computer Chemistry, Japan   13   177 - 178   2014.9

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    Tribo-Chemical Reaction of Molybdenum Dithiocarbamate on Diamond-Like Carbon Films: Quantum Chemical Molecular Dynamics Simulation

    DOI: 10.2477/jccj.2014-0034

  • Tight-binding quantum chemical molecular dynamics simulations of the low friction mechanism of fluorine-terminated diamond-like carbon films Reviewed

    Shandan Bai, Hiroki Murabayashi, Yoshihiko Kobayashi, Yuji Higuchi, Nobuki Ozawa, Koshi Adachi, Jean Michel Martin, Momoji Kubo

    RSC ADVANCES   4 ( 64 )   33739 - 33748   2014.7

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    The super-low friction mechanism of fluorine-terminated diamond-like carbon (F-terminated DLC) is investigated by using our tight-binding quantum molecular dynamics code and compared with that of hydrogen-terminated DLC (H-terminated DLC). Under a contact pressure of 1 GPa, F- and H-terminated DLC show smooth sliding and low friction coefficients of 0.07 and 0.04, respectively. The ion radius of fluorine is larger than that of hydrogen, which leads to the larger asperity of the F-terminated DLC surface. Thus, the friction coefficient of F-terminated DLC is slightly larger than that of H-terminated DLC. We also perform friction simulations under contact pressures of 3 and 7 GPa. Under a contact pressure of 3 GPa, the friction coefficients are 0.09 and 0.13 for F- and H-terminated DLC, respectively. F-terminated DLC shows the same friction behavior as seen under a contact pressure of 1 GPa, whereas the C-C bond formation reaction is observed at the interface of H-terminated DLC under a contact pressure of 3 GPa, leading to a slightly higher friction coefficient than when under a contact pressure of 1 GPa. Thus, under a contact pressure of 3 GPa, F- and H-terminated DLC show different friction behaviors. Furthermore, under a high contact pressure of 7 GPa, bond formation and dissociation are observed at the friction interface in F- and H-terminated DLC. C-C bond formation is observed more frequently in H-terminated DLC than in F-terminated DLC, and the lifetime of C-C bonds in H-terminated DLC is much longer. At this higher pressure, H-terminated DLC shows a high friction coefficient of 0.42 due to strong C-C bonds at the friction surface, whereas F-terminated DLC shows a low friction coefficient of 0.08. The strong repulsive interaction at the interface of F-terminated DLC that arises from the large negative charge and ion size of fluorine maintains the distance between DLC films under a high contact pressure. This prevents strong C-C bond formation at the friction surface, which results in the low friction properties of F-terminated DLC. We suggest that the friction properties of DLC films under a high contact pressure are improved by F termination.

    DOI: 10.1039/c4ra04065a

  • Effect of Tribochemical Reaction on Transfer-Film Formation by Poly(tetrafluoroethylene) Reviewed

    Tasuku Onodera, Kenji Kawasaki, Takayuki Nakakawaji, Yuji Higuchi, Nobuki Ozawa, Kazue Kurihara, Momoji Kubo

    JOURNAL OF PHYSICAL CHEMISTRY C   118 ( 22 )   11820 - 11826   2014.6

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    Understanding tribochemical reaction mechanisms is necessary to develop a novel resin material that can easily slide on metallic parts. For this purpose, the chemical reaction dynamics between poly(tetrafluoroethylene) (PTFE) resin and an aluminum surface were studied by using a quantum chemical molecular dynamics simulation [Onodera, T., et al. J. Phys. Chem. C 2014, 118, 5390-5396]. The study showed that the PTFE tribochemically reacted with the oxidized surface of aluminum, forming two chemical products, namely, aluminum fluoride and depolymerized PTFE with a carbon double bond at the terminus of the PTFE polymer chain. The carbon backbone was exposed by changing to a double bond configuration, although that in genuine PTFE is fully covered by fluorine atoms. The subsequent chemical reaction of the polymer that reacts with gaseous molecules in the atmosphere (i.e., nitrogen, oxygen, and water vapor) was first studied by density functional theory (DFT). The DFT calculation results show that the chemical reaction of PTFE with water vapor was the most likely to occur and that a carboxyl group was finally formed on the terminus of the PTFE chain. The effect of the chemical reaction with water vapor on formation of a PTFE transfer film on which directly affects tribological performance of the focusing system, was then investigated by a classical molecular dynamics method. By forming a carboxyl group as a reaction product with water vapor, the amount of PTFE transfer film on an aluminum fluoride surface (one of the tribochemical reaction products) was increased. On the other hand, less genuine PTFE (without a carboxyl group) was transferred to the aluminum fluoride. This study clarified that the transfer film is formed easily by the reaction of PTFE with atmospheric water vapor, which thereby improves the tribological performance of the PTFE/aluminum lubrication system.

    DOI: 10.1021/jp503331e

  • Chemical Reaction Mechanism of Polytetrafluoroethylene on Aluminum Surface under Friction Condition Reviewed

    Tasuku Onodera, Kenji Kawasaki, Takayuki Nakakawaji, Yuji Higuchi, Nobuki Ozawa, Kazue Kurihara, Momoji Kubo

    JOURNAL OF PHYSICAL CHEMISTRY C   118 ( 10 )   5390 - 5396   2014.3

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    To develop a novel shearing resin material, it is necessary to understand the mechanism of friction-induced chemistry during the friction process. For this purpose, the chemical reaction of the polytetrafluoroethylene (PTFE) resin on an aluminum surface during friction was first focused on and investigated by a quantum chemical molecular dynamics method. From our simulation, an aluminum atom on a native oxide of aluminum surface led to a tribochemical reaction, which included defluorination of PTFE and aluminum fluoride formation. It was inferred that the aluminum surface acted as a catalytic Lewis acid in which the fluorine atom was removed from the PTFE polymer chain. The tribological performance of the investigated system was reduced by the forming of aluminum fluoride since a self-lubrication by PTFE was inhibited by an interfacial electrostatic repulsion. On the basis of our study, it was suggested that the key to increase tribological performance was a chemical reaction between reactive defluorinated PTFE and environmental water vapor to form a novel functional group on the PTFE chain.

    DOI: 10.1021/jp412461q

  • Communication: Different behavior of Young's modulus and fracture strength of CeO2: Density functional theory calculations Reviewed

    Ryota Sakanoi, Tomomi Shimazaki, Jingxiang Xu, Yuji Higuchi, Nobuki Ozawa, Kazuhisa Sato, Toshiyuki Hashida, Momoji Kubo

    JOURNAL OF CHEMICAL PHYSICS   140 ( 12 )   2014.3

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    In this Communication, we use density functional theory (DFT) to examine the fracture properties of ceria (CeO2), which is a promising electrolyte material for lowering the working temperature of solid oxide fuel cells. We estimate the stress-strain curve by fitting the energy density calculated by DFT. The calculated Young's modulus of 221.8 GPa is of the same order as the experimental value, whereas the fracture strength of 22.7 GPa is two orders of magnitude larger than the experimental value. Next, we combine DFT and Griffith theory to estimate the fracture strength as a function of a crack length. This method produces an estimated fracture strength of 0.467 GPa, which is of the same order as the experimental value. Therefore, the fracture strength is very sensitive to the crack length, whereas the Young's modulus is not. (C) 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4869515

  • Theoretical Study on the Effect of Three-Dimensional Porous Structure on the Sintering of Nickel Nanoparticles in the Ni/YSZ Anode Reviewed

    Jingxiang Xu, Yuji Higuchi, Nobuki Ozawa, Kazuhisa Sato, Toshiyuki Hashida, Momoji Kubo

    SOLID OXIDE FUEL CELLS 13 (SOFC-XIII)   57 ( 1 )   2459 - 2464   2013.10

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    Understanding of the sintering mechanism of nickel nanoparticles in the Ni/YSZ anode is requested for long-term durability of solid oxide fuel cell. To elucidate the effects of a porous structure of the Ni/YSZ anode on the sintering, we investigated the sintering process in the Ni/YSZ anodes with different porosities by using our developed multi-nanoparticle molecular dynamics simulation method. We found that the nickel nanoparticle size significantly increased although the YSZ nanoparticles showed little change during the sintering in all the Ni/YSZ models. Since the decrease in the porosity leads to the decrease in the pore size of the YSZ framework, the sintering of the nickel nanoparticles in the Ni/YSZ model with the less porosity is more prevented by suppressing the neck growth in the small pore. On the other hand, the excessively large porosity increases the distance between the nickel nanoparticles and prevents the nickel nanoparticles from contacting.

    DOI: 10.1149/05701.2459ecst

  • Quantum chemical molecular dynamics study on film growth mechanisms of microcrystalline silicon solar cells Reviewed

    Takuya Kuwahara, Hiroshi Ito, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY   246   2013.9

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  • Quantum chemical molecular dynamics simulation on atomistic mechanisms of SiO2 etching process by fluorocarbon radicals Reviewed

    Ito Hiroshi, Kuwahara Takuya, Higuchi Yuji, Ozawa Nobuki, Samukawa Seiji, Kubo Momoji

    Abstracts of Papers of the American Chemical Society   246   2013.9

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    Quantum chemical molecular dynamics simulation on atomistic mechanisms of SiO2 etching process by fluorocarbon radicals

  • Different Crystal Growth Mechanisms of Si(001)-(2 x 1):H during Plasma-Enhanced Chemical Vapor Deposition of SiH3 and SiH2 Radicals: Tight-Binding Quantum Chemical Molecular Dynamics Simulations Reviewed

    Takuya Kuwahara, Hiroshi Ito, Kentaro Kawaguchi, Yuji Higuchi, Nobuld Ozawa, Momoji Kubo

    JOURNAL OF PHYSICAL CHEMISTRY C   117 ( 30 )   15602 - 15614   2013.8

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    We use tight-binding quantum chemical molecular dynamics to investigate the crystal growth mechanisms of H-terminated Si(001)-(2 x 1) during plasma-enhanced chemical vapor deposition of SiH3 and Sill, radicals. We find that crystal growth by SiH3 radical deposition consists of two stages: (1) the first SiH3 radical abstracts a surface-terminating H atom and produces a dangling bond, and (2) a second SiH3 radical is adsorbed on the dangling bond. Thus, at least two SiH3 radicals are required for generating a new Si Si bond. Interestingly, during SiH2 deposition, a SiH2 radical can be directly adsorbed onto a H-terminated site without H abstraction by another SiH2 radical. Thus, one SiH2 radical is sufficient for generating a new Si Si bond. This SiH2 radical crystal growth mechanism is different from the SiH3 radical mechanism. The direct adsorption process consists of a two-step chemical reaction: (1) the SiH2 radical abstracts a surface-terminating H atom and produces a dangling bond and a SiH3 radical, and (2) the SiH3 radical is adsorbed on the dangling bond. In addition, the crystal growth rate for SiH2 radicals is higher than that for SiH3 radicals, because generating one new Si Si bond requires either a single SiH2 radical or two SiH3 radicals. However, our simulations reveal that SiH2 deposition produces defective Si thin films because many dangling bonds are formed during crystal growth. Compared with SiH2 deposition, SiH3 deposition should therefore produce Si thin films of higher quality.

    DOI: 10.1021/jp4021504

  • Molecular Dynamics Simulation of Ni Nanoparticles Sintering Process in Ni/YSZ Multi-Nanoparticle System Reviewed

    Jingxiang Xu, Ryota Sakanoi, Yuji Higuchi, Nobuki Ozawa, Kazuhisa Sato, Toshiyuki Hashida, Momoji Kubo

    JOURNAL OF PHYSICAL CHEMISTRY C   117 ( 19 )   9663 - 9672   2013.5

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    We have developed a molecular dynamics (MD) simulation method to investigate the sintering of nickel nanoparticles in the nickel and yttria-stabilized zirconia (Ni/YSZ) anode of a solid oxide fuel cell (SOFC). The conventional sintering model consists of only two or three nickel nanoparticles. Therefore, it does not reflect the properties of the porous structure of the Ni/YSZ anode or reproduce realistic sintering. Our Ni/YSZ multi-nanoparticle MD simulation method uses a multi-nanoparticle model based on the porosity and are packed randomly in the simulation cell, and compressed to achieve the correct porosity. Furthermore, because the reliable potential parameters for MD simulation between nickel and YSZ have not been reported, we determine reliable interatomic potential parameters between nickel and YSZ by using the nonlinear least-squares method to fit the Morse potential function to interaction energies obtained by density functional theory. The sintering simulation using our Ni/YSZ multi-nanoparticle model and out potential parameters reveal that the YSZ nanoparticle framework suppresses the sintering of nickel nanoparticles by disrupting the growth of the neck between two nickel nanoparticles. The previously reported model of two nickel nanoparticles did not produce these results. Our multi-nanoparticle MD simulation method is effective for investigating the realistic sintering process in the porous structure of the Ni/YSZ anode and for designing durable anode structures for SOFCs.

    DOI: 10.1021/jp310920d

  • Chemical Reaction Dynamics of SiO2 Etching by CF2 Radicals: Tight-Binding Quantum Chemical Molecular Dynamics Simulations Reviewed

    Hiroshi Ito, Takuya Kuwahara, Yuji Higuchi, Nobuki Ozawa, Seiji Samukawa, Momoji Kubo

    JAPANESE JOURNAL OF APPLIED PHYSICS   52 ( 2 )   2013.2

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    The plasma etching of SiO2 by CF2 radicals was investigated using a newly developed etching process simulator based on tight-binding quantum chemical molecular dynamics (TB-QCMD). CF2 radicals were continuously irradiated on the SiO2(001) surface and then the dissociations of the C-F and Si-O bonds were observed. We also observed the generation of CO and CO2 molecules and Si-F bonds, which is in good agreement with previous experiments. The formation of etching holes was realized after the continuous irradiation of CF2 radicals. Furthermore, the effect of radical velocity on etching efficiency was also examined. The ratio of penetration depth to the width of irradiated atoms was examined for the evaluation of etching efficiency. The ratio increases as the irradiation velocity of CF2 radicals increases. Our TB-QCMD etching process simulator is capable of predicting etching rate and aspect ratio depending on the velocity of irradiated radicals. (C) 2013 The Japan Society of Applied Physics

    DOI: 10.7567/JJAP.52.026502

  • Development of Crystal Growth Simulator Based on Tight-Binding Quantum Chemical Molecular Dynamics Method and Its Application to Silicon Chemical Vapor Deposition Processes Reviewed

    Takuya Kuwahara, Hiroshi Ito, Yuji Higuchi, Nobuki Ozawa, Momoji Kubo

    JOURNAL OF PHYSICAL CHEMISTRY C   116 ( 23 )   12525 - 12531   2012.6

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    We have developed a crystal growth simulator based on tight-binding quantum chemical molecular dynamics (TB-QCMD) method and applied it to our crystal growth simulator to plasma-enhanced chemical vapor deposition (PECVD) for silicon thin film growth via SiH3 radicals on hydrogen-terminated Si(001). We successfully simulated the abstraction of a surface hydrogen atom by irradiated SiH3 radical and the formation of a dangling bond on the hydrogen-terminated Si(001) surface. SiH3 radical was subsequently adsorbed on this dangling bond. When these processes were repeated, the thin film grew. Thus, a detailed mechanism was successfully found for the chemical reaction and electron transfer dynamics of silicon thin film growth by PECVD.

    DOI: 10.1021/jp3002542

  • Fate of methanol molecule sandwiched between hydrogen-terminated diamond-like carbon films by tribochemical reactions: tight-binding quantum chemical molecular dynamics study Reviewed

    Kentaro Hayashi, Seiichiro Sato, Shandan Bai, Yuji Higuchi, Nobuki Ozawa, Tomomi Shimazaki, Koshi Adachi, Jean-Michel Martin, Momoji Kubo

    FARADAY DISCUSSIONS   156   137 - 146   2012.4

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    Recently, much attention has been given to diamond-like carbon (DLC) as a solid-state lubricant, because it exhibits high resistance to wear, low friction and low abrasion. Experimentally it is reported that gas environments are very important for improving the tribological characteristics of DLC films. Recently one of the authors in the present paper, J.-M. Martin, experimentally observed that the low friction of DLC films is realized under alcohol environments. In the present paper, we aim to clarify the low-friction mechanism of the DLC films under methanol environments by using our tight-binding quantum chemical molecular dynamics method. We constructed the simulation model in which one methanol molecule is sandwiched between two hydrogen-terminated DLC films. Then, we performed sliding simulations of the DLC films. We observed the chemical reaction of the methanol molecule under sliding conditions. The methanol molecule decomposed and then OH-termination of the DLC was realized and the CH3 species was incorporated into the DLC film. We already reported that the OH-terminated DLC film is very effective to achieve good low-friction properties under high pressure conditions, compared to H-terminated DLC films. Here, we suggest that methanol environments are very effective to realize the OH-termination of DLC films which leads to the good low-friction properties.

    DOI: 10.1039/c2fd00125j

  • Confinement causes opposite effects on the folding transition of a single polymer chain depending on its stiffness Reviewed

    Yuji Higuchi, Kenichi Yoshikawa, Takafumi Iwaki

    PHYSICAL REVIEW E   84 ( 2 )   2011.8

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    We investigated the folding transition between an elongated coil state and a compact state on a single polymer chain confined in a small space with different stiffness with the aid of Monte Carlo simulation. In a flexible polymer, the folding transition is retarded in a confined space. In contrast, the transition is promoted for a semiflexible chain, in which the discontinuity of the volume change occupied by a single chain is diminished by confinement. This unique confinement effect is interpreted in terms of conformational entropy and self-avoiding repulsive interaction.

    DOI: 10.1103/PhysRevE.84.021924

  • Torsional effect on the wrapping transition of a semiflexible polymer around a core as a model of nucleosome Reviewed

    Yuji Higuchi, Takahiro Sakaue, Kenichi Yoshikawa

    PHYSICAL REVIEW E   82 ( 3 )   2010.9

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    We investigated the effect of the torsional rigidity of a semiflexible chain on the wrapping transition around a spherical core, as a model of a nucleosome, the fundamental unit of chromatin. Through molecular dynamics simulation, we show that the torsional effect has a crucial effect on the chain wrapping around the core under the topological constraints. In particular, the torsional stress (i) induces the wrapping/unwrapping transition, and (ii) leads to a unique complex structure with an antagonistic wrapping direction which never appears without the topological constraints. We further examine the effect of the stretching stress for the nucleosome model in relation to the unique characteristic effect of the torsional stress on the manner of wrapping.

    DOI: 10.1103/PhysRevE.82.031909

  • Molecular dynamics of DNA and nucleosomes in solution studied by fast-scanning atomic force microscopy Reviewed

    Yuki Suzuki, Yuji Higuchi, Kohji Hizume, Masatoshi Yokokawa, Shige H. Yoshimura, Kenichi Yoshikawa, Kunio Takeyasu

    ULTRAMICROSCOPY   110 ( 6 )   682 - 688   2010.5

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    Nucleosome is a fundamental structural unit of chromatin, and the exposure from or occlusion into chromatin of genomic DNA is closely related to the regulation of gene expression. In this study, we analyzed the molecular dynamics of poly-nucleosomal arrays in solution by fast-scanning atomic force microscopy (AFM) to obtain a visual glimpse of nucleosome dynamics on chromatin fiber at single molecule level. The influence of the high-speed scanning probe on nucleosome dynamics can be neglected since bending elastic energy of DNA molecule showed similar probability distributions at different scan rates. In the sequential images of poly-nucleosomal arrays, the sliding of the nucleosome core particle and the dissociation of histone particle were visualized. The sliding showed limited fluctuation within similar to 50 nm along the DNA strand. The histone dissociation occurs by at least two distinct ways: a dissociation of histone octamer or sequential dissociations of tetramers. These observations help us to develop the molecular mechanisms of nucleosome dynamics and also demonstrate the ability of fast-scanning AFM for the analysis of dynamic protein-DNA interaction in sub-seconds time scale. (C) 2010 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.ultramic.2010.02.032

  • Chain length dependence of folding transition in a semiflexible homo-polymer chain: Appearance of a core-shell structure Reviewed

    Yuji Higuchi, Takahiro Sakaue, Kenichi Yoshikawa

    CHEMICAL PHYSICS LETTERS   461 ( 1-3 )   42 - 46   2008.8

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    The folding transition of single, long semiflexible polymers was studied with special emphasis on the chain length effect using Monte Carlo simulations. While a relatively short chain (10-25 Kuhn segments) undergoes a large discrete transition between swollen coil and compact toroid conformations, a long chain (50 Kuhn segments) exhibits an intrachain segregated state between the disordered coil and ordered toroid. (C) 2008 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.cplett.2008.06.068

  • Elucidation of conformational hysteresis on a giant DNA Reviewed

    Chwen-Yang Shew, Yuji Higuchi, Kenichi Yoshikawa

    JOURNAL OF CHEMICAL PHYSICS   127 ( 8 )   2007.8

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    The conformational behavior of a giant DNA mediated by condensing agents in the bulk solution has been investigated through experimental and theoretical approaches. Experimentally, a pronounced conformational hysteresis is observed for folding and unfolding processes, by increasing and decreasing the concentration of condensing agent (polyethylene glycol) (PEG), respectively. To elucidate the observed hysteresis, a semiflexible chain model is studied by using Monte Carlo simulations for the coil-globule transition. In the simulations, the hysteresis loop emerges for stiff enough chains, indicating distinct pathways for folding and unfolding processes. Also, our results show that globular state is thermodynamically more stable than coiled state in the hysteresis loop. Our findings suggest that increasing chain stiffness may reduce the chain conformations relevant to the folding pathway, which impedes the folding process.

    DOI: 10.1063/1.2759925

  • Conformational Hysteresis on A Giant DNA Molecule

    Shew Chwen-Yang, Higuchi Yuji

    busseikenkyu   87   127 - 127   2006.10

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    Conformational Hysteresis on A Giant DNA Molecule

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Books

  • 表面・界面技術ハンドブック : 材料創製・分析・評価の最新技術から先端産業への適用、環境配慮まで

    伊藤寿, 桑原卓哉, 樋口祐次, 尾澤伸樹, 久保百司(Role:Joint author)

    エヌ・ティー・エス  2016.4 

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    Responsible for pages:総ページ数:5, 13, 7, 796, 21p, 図版8p   Language:Japanese  

Presentations

  • Large-Scale Molecular Dynamics Simulations for Deformation and Fracture Processes of Crystalline Polyethylene Invited

    Yuji Higuchi

    CIMTEC 2024 - Global Conference “Materials in an Explosively Growing Informatics World”  2024.6 

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    Event date: 2024.6

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  • 水の回転拡散に対する第二水和圏の重要性

    樋口祐次、菱田真史

    第37回分子シミュレーション討論会  2023.12 

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    Event date: 2024.4

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:福井   Country:Japan  

  • 高分子材料の変形・破壊に関する粗視化分子動力学シミュレーション

    樋口祐次

    日本機械学会 第36回計算力学講演会(CMD2023)  2023.10 

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    Event date: 2023.10

    Language:Japanese   Presentation type:Oral presentation (general)  

    Country:Japan  

  • 分子シミュレーションによる分子の水和状態と水の回転拡散

    樋口祐次、菱田真史

    第72回高分子討論会  2023.9 

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    Event date: 2023.9

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:高松   Country:Japan  

  • 荷電リン脂質二重膜の分子シミュレーション

    樋口祐次、伊藤弘明、下川直史

    第71回高分子討論会  2022.9 

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    Event date: 2023.5

    Language:Japanese   Presentation type:Oral presentation (general)  

    Venue:札幌   Country:Japan  

  • Fracture Process of Polymer Materials by Molecular Simulation Invited

    Yuji Higuchi

    The 71st SPSJ Annual Meeting  2022.5 

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    Country:Other  

    Fracture Process of Polymer Materials by Molecular Simulation

  • Fracture Process of Polymer Materials by Molecular Simulation Invited

    Yuji Higuchi

    The 71st SPSJ Annual Meeting  2022.5 

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    Event date: 2022.5

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  • Hydrogen Production Process From Vibrationally-Excited Methane By First-Principles Molecular Dynamics Simulation Invited

    Naoki Yokoyama, Yuji Higuchi, Nobuki Ozawa, Hiroo Yugami, Momoji Kubo

    The Second Working Group Meeting of ACCMS (Asian Consortium on Computational Materials Science) on Computational Design of Materials for Energy Conversation and Storage  2014.6 

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  • First-Principles Molecular Dynamics Simulation on Hydrogen Generation Processes by Vibrationally-Excitation Invited

    Yuji Higuchi, Naoki Yokoyama, Nobuki Ozawa, Hiroo Yugami, Momoji Kubo

    The 9th International Conference on Computational Physics (ICCP9)  2015.1 

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  • 高分子の劣化と破壊:量子化学と統計物理の融合 Invited

    樋口祐次

    第6回CSJ化学フェスタ2016  2016.11 

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  • 分子論的立場からのポリエチレンの破壊シミュレーション Invited

    樋口祐次

    賢材研究会幹事会  2018.8 

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  • 高分子材料の変形・破壊プロセス解明に向けた大規模粗視化分子動力学 シミュレーション Invited

    樋口 祐次

    新化学技術推進協会 先端化学・材料技術部会 コンピュータケミストリ分科会高分子WG 講演会  2018.11 

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  • 分子シミュレーョンによる結晶性高分子の劣化と破壊 Invited

    樋口 祐次

    18-5 ポリマーフロンティア21  2019.1 

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  • Mechanical Properties of Semicrystalline Polymers at the Molecular Level by Coarse-Grained Molecular Dynamics Simulation Invited International conference

    樋口 祐次

    The Second International Conference of Polymeric and Organic Materials in Yamagata University  2019.12 

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    Mechanical Properties of Semicrystalline Polymers at the Molecular Level by Coarse-Grained Molecular Dynamics Simulation

  • 高分子材料の内部構造と破壊メカニズムおよびその解析方法 Invited

    樋口祐次

    株式会社R&D支援センター セミナー  2021.3 

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  • 分子シミュレーションで見る水圏機能材料 Invited

    樋口祐次

    第11回CSJ化学フェスタ2021  2021.10 

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  • 分子シミュレーションによる高分子材料の破壊プロセス Invited

    樋口祐次

    大阪大学工業会 産学高分子塾 10 周年記念公開セミナー2 高分子の架橋・材料設計に限界はあるか?求める機能に応じた設計とその開発動向  2021.12 

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  • リン脂質二重膜上の水分子のダイナミクス Invited

    樋口祐次

    Mini-Symposium on Liquids 2022  2022.7 

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  • 分子シミュレーションによる高分子材料の内部構造と破壊メカニズムの解析 Invited

    樋口祐次

    株式会社R&D支援センター セミナー  2023.1 

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  • ソフトマター材料の変形・破壊・自己組織化に関する分子シミュレーション Invited

    樋口祐次

    日本接着学会 東北・北海道支部講演会  2023.3 

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  • 高分子材料の機能物性に関するシミュレーションの基礎 Invited

    樋口祐次

    第27回高分子計算機科学研究会講座  2023.7 

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  • 分子スケールにおける高分子材料の内部構造と破壊メカニズム Invited

    樋口祐次

    株式会社R&D支援センター セミナー  2024.1 

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  • 結晶性高分子の分子スケールにおける変形・破壊プロセスと低劣化・高耐久に向けた材料設計指針 Invited

    樋口祐次

    サイエンス&テクノロジー株式会社 セミナー  2024.2 

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  • 分子シミュレーションを用いた高分子材料の破壊メカニズムの解析 Invited

    樋口祐次

    株式会社技術情報協会 セミナー  2024.3 

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  • 分子シミュレーションによるソフトマターの構造・物性の理解 Invited

    樋口祐次

    日本物理学会 2024年春季大会  2024.3 

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  • ソフトマター周囲の水分子の回転ダイナミクス Invited

    樋口祐次

    第15回分子集合系計算科学セミナー  2024.3 

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  • 高分子材料の変形・破壊メカニズムと耐久性向上のポイント Invited

    樋口祐次

    株式会社日本テクノセンター セミナー  2024.6 

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MISC

  • 分子動力学法による高分子材料のトライボロジーシミュレーション ―ポリマーブラシの摩耗メカニズムの解析― Reviewed

    樋口 祐次, 高桑 諒, 大谷 優介, 久保 百司

    トライボロジスト   2024.3

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    DOI: https://doi.org/10.18914/tribologist.69.03_195

  • 荷電脂質膜の秩序形成:実験と粗視化分子動力学シミュレーションの融合

    下川 直史, 伊藤 弘明, 樋口祐次

    分子シミュレーション学会誌「アンサンブル」   2021.10

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  • 高分子材料の破壊に関する粗視化シミュレーション

    樋口祐次

    分子シミュレーション学会誌「アンサンブル」   2020.7

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    DOI: 10.11436/mssj.22.216

  • 荷電脂質膜ベシクルの相分離・自発的変形・ナノ粒子の透過 Reviewed

    下川 直史, 伊藤 弘明, 樋口 祐次

    コロイドおよび界面化学部会ニュースレター   2019.12

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    Phase separation, spontaneous deformation, and nanoparticle uptake of charged lipid membranes

  • 8pAQ-12 ポリエチレンの変形による劣化(8pAQ 高分子・ゲル,領域12(ソフトマター物理・化学物理・生物物理))

    樋口 祐次, 尾澤 伸樹, 久保 百司

    日本物理学会講演概要集   2014.8

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    8pAQ-12 Chemical reaction of polyethylene caused by deformation

  • 5PM3-PMN-019 量子分子動力学法と第一原理計算による窒化ガリウムの化学機械研磨プロセスの理論的解明(OS6 マイクロナノトライボロジー,ポスターセッション)

    河口 健太郎, 樋口 祐次, 尾澤 伸樹, 久保 百司

    マイクロ・ナノ工学シンポジウム   2013.11

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    5PM3-PMN-019 Quantum Chemical Molecular Dynamics and First-Principles Study on Chemical Mechanical Polishing of Gallium Nitride
    We performed the chemical mechanical polishing (CMP) process simulations of GaN(0001) by a SiO_2 cluster in aqueous NaOH and H_2O_2 solution. In aqueous NaOH solution, OH" ions adsorbed on the Ga-top site of the GaN surface. In aqueous H_2O_2 solution, OH radicals adsorbed on the hollow site of the GaN surface and weakened the Ga-N back-bond. Therefore, we suggest that the OH radical is effective for GaN-CMP as compared with the OH ion. However, we did not observe the subsequent chemical reactions and the polishing process of the GaN surface in both environments. We performed the CMP process simulation of GaN(0001) by a SiO_2 cluster with many OH radicals produced by a catalyst. After the OH radicals occupied all the hollow sites of the GaN surface, and another OH radical attacked a Ga atom of GaN surface, we observed the diffusion of the OH species adsorbed on the GaN surface into the GaN bulk and generation of gallium oxide and N_2 molecules.

  • 6PM3-PMN-018 計算科学手法を用いた炭化ケイ素の水潤滑における表面特性変化の解明(OS6 マイクロナノトライポロジー,ポスターセッション)

    小林 康彦, 佐藤 誠一亮, 白 珊丹, 樋口 祐次, 尾澤 伸樹, 足立 幸志, 久保 百司

    マイクロ・ナノ工学シンポジウム   2013.11

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    6PM3-PMN-018 Computational Simulation on Change of Surface Property in Water Lubrication of Silicon Carbide
    Friction of silicon carbide (SiC) films under water environment shows a low friction coefficient experimentally. Understanding of the mechanism is essential to improve friction characteristics of the SiC films. However, it is difficult to directly obtain atomic-scale dynamics with chemical reactions by experiments. In this study, our purpose is to reveal the chemical reactions of the SiC surface under water lubrication by our first-principles molecular dynamics (FPMD) and tight-binding quantum chemical molecular dynamics (TB-QCMD) methods. First, we performed the simulation of SiC sliding in water by our FPMD method and then Si-OH and C-H bonds were generated on the surface. Next, we also simulated the larger model of SiC in water environment by our TB-QCMD method. Then, the generation of Si-O-Si bonds and the growth of Si-O-Si bond chains were observed. We suggest that this growth relates to the low friction property of the SiC surface.

  • 6AM2-C-7 計算科学シミュレーションによるSiドープダイヤモンドライクカーボンの構造変化のメカニズム解明(6AM2-C OS6 マイクロナノトライボロジー(1))

    白 珊丹, 小林 康彦, 佐藤 誠一亮, 樋口 祐次, 尾澤 伸樹, 足立 幸志, 久保 百司

    マイクロ・ナノ工学シンポジウム   2013.11

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    6AM2-C-7 The Structure Transition of Si Doped Diamond Like Carbon Using Computational Simulation
    Si doped DLC films as solid lubricant exhibit excellent tribological properties of low friction and high wear resistance. One of the low friction reasons is the structure change from sp^3 carbon to sp^2 carbon on the surface of DLC films by Si doping. In this study, to reveal the mechanism of the structure change of the DLC surface by Si doping, we investigate the surface structure of the Si doped diamond using the first-principles calculation. The results show the structure change from six-membered ring to five-membered ring on the surface of Si doped diamond since a Si atom has larger atomic radius than a C atom. Furthermore, the structure change from sp^3 carbon to sp^2 carbon results in the generation of graphene, which would affect the low friction of Si doped DLC films.

  • 6AM2-C-6 Tight-Binding量子分子動力学法と第一原理分子動力学法による窒化炭素腹界面の低摩擦機構に関する研究(6AM2-C OS6 マイクロナノトライボロジー(1))

    佐藤 誠一亮, 小林 康彦, 白 珊丹, 樋口 祐次, 尾澤 伸樹, 足立 幸志, 久保 百司

    マイクロ・ナノ工学シンポジウム   2013.11

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    6AM2-C-6 Low Friction Mechanism of Carbon Nitride Based on Tight-Binding Quantum Chemical Molecular Dynamics and First-Principles Molecular Dynamics Simulations
    We performed friction simulations of hydrogen terminated carbon nitride (H-CNX) using our first-principles molecular dynamics (FPMD) and tight-binding quantum chemical molecular dynamics (TB-QCMD) simulators. In FPMD simulation, H-CN_X showed low friction coefficient of 0.15 and 0.10 at 5 and 10 GPa, respectively. This is because terminated hydrogen atoms prevented the bond generation at the films interface. In TB-QCMD simulation, under 1 GPa, H-CN_X and H-DLC also showed low friction coefficients of 0.05 because terminated hydrogen atoms prevented the bond generation at the films interface. On the other hand, under 5 GPa, while H-CN_X showed a low friction coefficient of 0.07, a friction coefficient of H-DLC takes a high value of 0.42. Although C-C bonds were generated at the interface of H-DLC films under high pressure, nitrogen atoms of H-CN_X prevented C-C bond generation at the interface. We found that H-CN_X is more stable and shows lower friction than H-DLC under high pressure.

  • 6AM2-C-4 シリカ砥粒によるα-Al_2O_3基板の化学機械研磨プロセスの計算科学手法を用いた解析(6AM2-C OS6 マイクロナノトライボロジー(1))

    尾澤 伸樹, 周 康, 會澤 豪大, 樋口 祐次, 久保 百司

    マイクロ・ナノ工学シンポジウム   2013.11

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    6AM2-C-4 CMP Process Analysis of α-Al_2O_3 Substrate by Silica Abrasive Grain via Computational Method
    In order to reveal a chemical mechanical polishing (CMP) mechanism of a sapphire substrate by a colloidal silica abrasive grain, we investigated a polishing process of an α-Al_2O_3(0001) surface by a SiO_2 cluster under water environment by a first-principles calculation. The results show that the mechanical pressing by the SiO_2 cluster and the chemical reaction with a H_2O molecule introduce the break of the Al-O bond of the α-Al_2O_3(0001) surface. In addition, after the chemical reaction with H_2O, an Al(OH)_3 molecule is generated and desorbs from the α-Al_2O_3 surface in the CMP process.

  • I131 第一原理分子動力学法によるフッ素系高分子電解質の分解メカニズムの解明(OS-5:燃料電池・二次電池関連研究の新展開(3))

    小林 顕, 樋口 祐次, 尾澤 伸樹, 久保 百司

    熱工学コンファレンス講演論文集   2013.10

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    I131 Clarification of Mechanism for Decomposition of Perfluorinated Polymer Electrolyte by First-Principles Molecular Dynamics Method
    To clarify the degradation mechanism of the perfluorinated polymer electrolytes in polymer electrolyte fuel cells, we studied the decomposition process of the end group of these polymers using the first-principles molecular dynamics method. We successfully clarified that the polymer end model of CF_3CF_2CF_2OH reacts with a hydroxyl radical to generate a water molecule and CF_2O. After CF_2O was desorbed, polymer end model became CF_3CF_2・. CF_3CF_2・reacts with another hydroxyl radical to reproduce the hydroxyl end group. Therefore, it was revealed that cyclic degradation reactions like the unzipping mechanism occur when CF_3CF_2CF_2OH reacts with hydroxyl radicals. Furthermore, it was revealed that the CF_2O desorption reaction is inhibited by surrounding water molecules, while the HF desorption reaction from CF_3CF_2CF_2OH is promoted.

  • I132 固体高分子形燃料電池におけるPt-Ru合金ナノ粒子触媒活性の第一原理計算による検討(OS-5:燃料電池・二次電池関連研究の新展開(3))

    尾澤 伸樹, 樋口 祐次, 久保 百司

    熱工学コンファレンス講演論文集   2013.10

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    I132 A First-Principles Investigation on Catalyst Activity of Pt-Ru Alloy Nano Particle in Polymer Electrolyte Fuel Cell
    A PtRu alloy nano-particle attracts attention as an anode catalyst in a polymer electrolyte fuel cell because of its higher tolerability for CO poisoning than a Pt nano-particle. To reveal the mechanism of the high tolerability for CO in the PtRu alloy nano-particle, we investigated adsorption process of a CO molecule on the Pt and PtRu alloy nano-particles by first-principles calculation. The results show that the bond length of the CO molecule adsorbed on the PtRu alloy nano-particle is longer than that on the Pt nano-particle. This indicates that the PtRu alloy nano-particle oxidizes a CO molecule to a CO_2 molecule more easily than the Pt nano-particle. In addition, the CO molecule is more difficult to adsorb on the Pt atom in the PtRu alloy nano-particle than that in the Pt nano-particle.

  • J044013 第一原理計算と粗視化分子動力学法によるポリエチレンの化学劣化が耐久性に与える影響([J044-01]ソフトマター・イノベーション(1))

    樋口 祐次, 尾澤 伸樹, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2013.9

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    J044013 Chemical Aging Effect on Toughness of Polyethylene by First-Principles Calculation and Coarse-Grained Molecular Dynamics Simulation
    We study the degradation process and toughness of polymer composites by first-principles calculation and coarse-grained molecular dynamics simulation. To clarify the effect of water at the filler surface on the degradation of polymers, we calculate H abstraction of polyethylene by OH and H radicals. Activation barriers are 3.2 and 5.0 kcal/mol and these reactions easily occur at room temperature. Therefore, water molecules generate radical and cause degradation. Then, we study the toughness of melt and semicrystalline polymers with filler against the stretching by coarse-grained molecular dynamics simulation. In melt polymer, fillers increase the toughness but the toughness of degraded one decrease more than that without fillers. On the other hand, in semicrystalline polymer, fillers decrease the toughness but the toughness of degraded one decrease less than that without fillers.

  • J061054 量子分子動力学法に基づくリチウムイオン電池の劣化プロセスシミュレーション(〔J061-05〕燃料電池・二次電池におけるナノ・マイクロ現象とマクロ性能(5):各種電池)

    中村 耕輔, 樋口 祐次, 尾澤 伸樹, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2013.9

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    J061054 Degradation Process Simulation of Lithium-Ion Battery by Quantum Chemical Molecular Dynamics Method
    To clarify the degradation mechanism of lithium-ion battery cathode, we studied the degradation process of the cathode caused by a chemical reaction with ethylene carbonate (EC) via our tight-binding quantum chemical molecular dynamics (TB-QCMD) method. We simulated the dynamics of the chemical reaction of LiCoO_2(010) surface and EC. In addition, our calculated atomic bond population revealed that a Co-O bond of the LiCoO_2(010) surface weakened when an O atom bound with a C atom of EC. This weakening of the Co-O bond indicates that the O atom of the surface is easily removed from the surface and the Co atom is reduced. It is known that the structural change of the cathode after the reduction of the Co atom causes the degradation of the lithium-ion battery cathode. Thus, we suggested that the adsorption of EC resulting in the reduction of Co atoms was the initial process of the degradation of the lithium-ion battery cathode.

  • J061033 フッ素系高分子電解質における側鎖分解プロセスの第一原理分子動力学シミュレーション(〔J061-03〕燃料電池・二次電池におけるナノ・マイクロ現象とマクロ性能(3):PEFC電極・電解質膜)

    小林 顕, 樋口 祐次, 尾澤 伸樹, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2013.9

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    J061033 First-Principle Molecular Dynamics Simulation of Decomposition Process in Side Chain of Perfluorosulfonic Acid Polymer Electrolyte
    To clarify the degradation mechanism of perfluorosulfonic acid (PFSA) membranes in polymer electrolyte fuel cells, we studied the decomposition process of PFSA side chain by radical species using the first-principles molecular dynamics method. This approach is possible to simulate real-time reactions from a viewpoint of atomic scale and reveal novel reaction pathways that traditional static methods may overlook. We investigated the reactions of OH and H radicals with the side chain model of CF_3CF_2CF_2SO_3H. In the reaction with a OH radical, a water molecule was generated when the OH radical abstracted the hydrogen atom from the side chain. An analysis of the interatomic distances and potential energy profiles revealed that the hydrogen bond between the OH radical and the oxygen atom in the sulfo group lowered the activation energy for the hydrogen abstraction. On the other hand, a H radical reacted with not the hydrogen atom but the oxygen atom in the sulfo group even though the activation energy for the reaction with the oxygen atom is higher than that with the hydrogen atom. This is because the hydrogen atom can escape from the approach of the H radical due to the small radius and mass, while the oxygen atom reacts with the radical due to the large radius and mass relative to the hydrogen atom. Moreover, this result indicates that it is important for clarification of the degradation mechanism to take account of not only statics but also dynamics.

  • J061012 計算科学シミュレーションによるNi/YSZ電極の劣化プロセスの解明(〔J061-01〕燃料電池・二次電池におけるナノ・マイクロ現象とマクロ性能(1):SOFC内現象)

    許 競翔, 樋口 祐次, 尾澤 伸樹, 佐藤 一永, 橋田 俊之, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2013.9

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    J061012 Investigation of the Degradation Process of the Ni/YSZ Electrode Using Computer Simulation
    Sintering of nickel nanoparticles during the long-term operation leads to the degradation of the Ni/YSZ anode. To prevent the sintering, understanding of the sintering process in the Ni/YSZ anode with a porous structure is needed. In this work, to investigate the effect of porosity of the Ni/YSZ anode on the sintering, we modeled the Ni/YSZ multi-nanoparticle models with the porosity of 0.25 and 0.45 and simulated the sintering in the models by using our developed multi-nanoparticle molecular dynamics simulation method that can consider the effects of the properties of the porous structure such as porosity and YSZ nanoparticle framework, etc. It was revealed that the YSZ framework prevented the sintering of nickel nanoparticles in the small pore of the YSZ framework. Furthermore, it was found that the degree of sintering of nickel nanoparticles in the Ni/YSZ model with the porosity of 0.25 is smaller than that of 0.45, because the decrease in the porosity leads to the decrease in the pore size of the YSZ framework. Thus, we suggest that decreasing the porosity of Ni/YSZ anode can inhibit the sintering of nickel nanoparticles.

  • J061055 エチレングリコールを用いたアルカリ形燃料電池における反応活性の第一原理計算による検討(〔J061-05〕燃料電池・二次電池におけるナノ・マイクロ現象とマクロ性能(5):各種電池)

    千枝 繁樹, 樋口 祐次, 尾澤 伸樹, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2013.9

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    J061055 First-Principles Investigation on Reaction Activity in Alkaline Fuel Cell with Ethylene Glycol
    To develop the inexpensive non-noble highly-active and selective catalyst of the alkaline fuel cell (AFC), we investigated ethylene glycol oxidation on transition metal surfaces such as Fe(001), Co(0001), and Ni(111) based on first principles calculation. To clarity which surface has high activity for ethylene glycol oxidation, we calculate the activation energies for O-H and C-H bond dissociations on all surfaces. Then, we find the lowest activation energies for O-H and C-H bond dissociations on Fe(001). We also calculate the activation energies for C-C bond dissociations on Fe(001) and Ni(111) to reveal the selectivity of the catalyst. The comparison among the activation energies for O-H, C-H, and C-C bond dissociations shows the higher selectivity for the ethylene glycol oxidation on Fe(001) than that on Ni(111). Thus, Fe(001) is expected for the highly-active and selective catalytic material of the AFC.

  • 27pKP-8 フィラーが高分子の劣化と耐久性に与える影響(高分子一般,領域12(ソフトマター物理,化学物理,生物物理))

    樋口 祐次, 尾澤 伸樹, 久保 百司

    日本物理学会講演概要集   2013.8

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    Effect of fillers on the degradation and toughness of polymer composites

  • J056032 第一原理分子動力学法を用いた高分子電解質膜の劣化シミュレーション

    小林 顕, 樋口 祐次, 尾澤 伸樹, 島崎 智実, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2012.9

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    J056032 The Degradation Simulation of the Polymer Electrolyte Membrane Based on First-Principles Molecular Dynamics
    To clarify the degradation mechanism of proton exchange membrane (PEM) in a polymer electrolyte fuel cell (PEFC), we studied the degradation process of Nafion widely used as PEM by the first-principles molecular dynamics (FPMD) method. FPMD calculations were carried out using our "Violet" program, based on density functional theory (DFT) with B3LYP exchange-correlation functional and 6-31G (d) basis sets. We successfully clarified the dynamics of the reactions in which the main chain end was decomposed by OH radicals. Moreover, it was revealed that the reaction pass differs whether there are water molecules or not in the reaction system. In order to elucidate the difference, we calculated activation energies in these reactions by DFT method. The activation energy of the reaction with water molecules is lower than that of without a water molecule. Therefore, we conclude that water molecules work as a catalyst in the degradation reaction.

  • J056046 計算科学シミュレーションを用いた固体酸化物形燃料電池用ガドリニアドープセリア電解質の破壊メカニズムの解明

    坂之井 遼太, 許 競翔, 樋口 祐次, 尾澤 伸樹, 島崎 智実, 佐藤 一永, 橋田 俊之, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2012.9

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    J056046 Computational Simulation on Fracture Properties of Gadolinia Doped Ceria Electrolytes for Solid Oxide Fuel Cell
    In this paper, we discuss the fracture properties of gadolinia doped ceria (GDC) electrolytes for solid oxide fuel cell (SOFC), based on molecular dynamics (MD) simulation and density functional theory (DFT). The ceria based materials like a GDC are expected as electrolytes to lower the operating temperature, however, the short lifetime of GDC prevents their wide applications. Therefore, we executed the tensile test using the MD simulation and DFT calculation and obtained the Young's modulus and the fracture stress of the GDC. Both indicate phase transition where the oxygen coordination number of Ce^<4+> ions changes from eight to six after the yield point. Furthermore, we calculated the Young's modulus and the fracture stress as functions of oxygen concentration. This result shows that the Young's modulus decreases linearly when the oxygen concentration increases, while the fracture stress is insensitive to the changes. This tendency is in good agreement with experimental data qualitatively. We also discuss the effect of steam condition on the fracture properties of GDC, and find the crack advance of GDC is accelerated by the chemical reaction with H_2O molecules.

  • J056045 分子動力学シミュレーションによる固体酸化物形燃料電池アノードのシンタリングに及ぼすドーパントの影響

    許 競翔, 坂之井 遼太, 樋口 祐次, 尾澤 伸樹, 島崎 智実, 佐藤 一永, 橋田 俊之, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2012.9

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    J056045 Molecular Dynamics Simulation of Dopant Effects on Sintering Process in Solid Oxide Fuel Cell Anode
    The dopant effects on the sintering process of nickel nanoparticles in the nickel and doped zirconia cermet anode were investigated by using molecular dynamics (MD) simulation. In this study, we unraveled the differences of the sintering process, the surface area of the nickel nanoparticles, and the triple phase boundary (TPB) length between the Ni/YSZ and the Ni/ScSZ systems. According to the simulation results, we observed that the extent of sintering in the Ni/YSZ is larger than that in the Ni/ScSZ due to the dopant effect. These observations revealed that the sintering on the YSZ surface takes place more easily than that on the ScSZ surface. Then, the mechanism of the dopant effect on the sintering of nickel nanoparticles is investigated by using density functional theory (DFT). It was found that the low adsorption energy between the nickel and the doped zirconia decreases the movement of the nickel nanoparticles and inhibits the sintering of the nickel nanoparticles on the doped zirconia surface.

  • J056034 アルカリ形燃料電池におけるエチレングリコール酸化触媒の計算科学手法による高速スクリーニング

    尾澤 伸樹, 小林 顕, 冨土田 実央, 樋口 祐次, 久保 百司

    年次大会 : Mechanical Engineering Congress, Japan   2012.9

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    J056034 High-Speed Screening of Ethylene Glycol Oxidation Catalyst for Alkaline Fuel Cells via Computational Science Method
    In this study, to elucidate highly-selective catalyst materials for an oxidation reaction of an ethylene glycol (HOCH_2CH_2OH) to an oxalic acid ((COOH)_2), we performed high-speed screening of effective metal catalyst for partial oxidation of HOCH_2CH_2OH via first-principles calculations. Here, to screen effective element for the partial oxidation process, we investigated the oxidation reactivity of the ethylene glycol on the Fe(001), Ni(111), Co(0001), Cu(111), and Pt(111) surfaces. Fe, Ni, and Co are found to be effective for the dissociations of O-H and C-H bonds of HOCH_2CH_2OH, which are elementary reactions process of the above partial oxidation. In addition, the dissociation of the C-H bond is found to require the step structure on the metal catalyst surface. Furthermore, we revealed that Pt completely oxidizes an ethylene glycol to a carbon dioxide since the C-C bond is broken by Pt at the oxidation process. Therefore, we suggest that highly-selective catalyst materials for the partial oxidation of the ethylene glycol consist of Fe, Ni, and Co.

  • 24aAH-4 化学劣化した半結晶高分子の破壊シミュレーション(24aAH 高分子,領域12(ソフトマター物理,化学物理,生物物理))

    樋口 祐次, 尾澤 伸樹, 久保 百司

    日本物理学会講演概要集   2012.3

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    24aAH-4 Chemical Aging Effect on the Fracture Process of Semicrystalline Polymers Studied by Molecular Dynamics Simulation

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Professional Memberships

  • ソフトマター研究会

  • 分子シミュレーション学会

  • 日本化学会

  • 日本物理学会

  • 高分子学会

  • 日本機械学会

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Committee Memberships

  • 分子シミュレーション学会   Organizer   Domestic

    2023.1 - 2024.12   

  • 分子シミュレーション学会   編集幹事   Domestic

    2023.1 - 2024.12   

  • 日本物理学会   Steering committee member   Domestic

    2016.10 - 2017.9   

  • 日本物理学会   領域12運営委員(ソフトマター)   Domestic

    2016.10 - 2017.9   

Academic Activities

  • 分子シミュレーション学会誌「アンサンブル」

    2023.1 - 2024.12

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    Type:Academic society, research group, etc. 

  • Screening of academic papers

    Role(s): Peer review

    2023

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    Type:Peer review 

    Number of peer-reviewed articles in foreign language journals:5

  • 所外組織委員

    物性研究所スパコン共同利用・CCMS合同研究会「計算物質科学の新展開2022」  ( Japan ) 2022.5

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    Type:Competition, symposium, etc. 

  • Screening of academic papers

    Role(s): Peer review

    2022

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    Type:Peer review 

    Number of peer-reviewed articles in foreign language journals:3

  • 学会実行委員

    物性研究所スパコン共同利用・CCMS合同研究会「計算物質科学の新展開2020」  ( Japan ) 2020.12

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    Type:Competition, symposium, etc. 

  • 学会実行委員

    物性研究所スパコン共同利用・CCMS合同研究会「計算物質科学の新展開」  ( Japan ) 2019.4

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    Type:Competition, symposium, etc. 

  • 学会実行委員

    第17回 関東ソフトマター研究会  ( Japan ) 2018.8

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  • 学会実行委員

    物性研究所スパコン共同利用・CCMS合同研究会「計算物質科学の今と未来」  ( Japan ) 2018.4

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    Type:Competition, symposium, etc. 

  • 学会実行委員

    つくばソフトマター研究会2017  ( Japan ) 2017.5

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    Type:Competition, symposium, etc. 

  • 分子シミュレーション学会誌「アンサンブル」

    2017.1 - 2020.12

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    Type:Academic society, research group, etc. 

  • 学会実行委員

    第28回分子シミュレーション討論会  ( Japan ) 2014.11

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  • 学会実行委員

    トライボロジー会議2014秋  ( Japan ) 2014.11

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Research Projects

  • 分子シミュレーションを用いたらせん構造をもつ結晶性高分子の機械的特性の解明と設計指針の提案

    2024

    単年度研究助成

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    Grant type:Contract research

  • 計算科学による水圏機能材料の設計

    Grant number:19H05718  2019 - 2023

    Japan Society for the Promotion of Science・Ministry of Education, Culture, Sports, Science and Technology  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

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    Authorship:Coinvestigator(s)  Grant type:Scientific research funding

  • 分子論的立場からの結晶性高分子の変形・破壊プロセス

    Grant number:17K14534  2017 - 2018

    Grants-in-Aid for Scientific Research  Grant-in-Aid for Young Scientists(A)or(B)

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    Authorship:Principal investigator  Grant type:Scientific research funding

  • 超低摩擦技術開発のための量子化学に基づく「なじみ」と「焼付き」の理論基盤の構築

    Grant number:26249011  2014 - 2016

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research  Grant-in-Aid for Scientific Research (A)

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    Authorship:Coinvestigator(s)  Grant type:Scientific research funding

  • 高分子の劣化と破壊:量子化学と統計物理の融合

    2013 - 2016

    科学技術振興機構 さきがけ

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    Authorship:Principal investigator  Grant type:Contract research

  • 半屈曲高分子鎖の折り畳み転移:実験・理論両面からのアプローチ

    2009 - 2010

    Japan Society for the Promotion of Science  Research Fellowships for Young Scientists

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    Authorship:Principal investigator  Grant type:Joint research

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FD Participation

  • 2022.4   Role:Participation   Title:令和4年度 第1回全学FD(新任教員の研修)The 1st All-University FD (training for new faculty members) in FY2022

    Organizer:University-wide

Outline of Social Contribution and International Cooperation activities

  • 国際交流
    日本学術振興会 二国間交流事業共同研究(スロベニア)
    「荷電脂質膜の相分離と秩序構造:電解質価数の効果」(2021-2022年度)に参画
    (新型コロナウイルス感染症の影響のため一年延長)