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DOI： 10.1039/d3sm00222e

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DOI： 10.1021/jacs.2c12348

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DOI： 10.1021/acs.macromol.1c01894

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DOI： 10.1039/d1cc05560g

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DOI： 10.1021/acsami.1c09468

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DOI： 10.1021/acs.langmuir.1c00967

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DOI： 10.1021/acs.langmuir.1c00727

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DOI： 10.1021/acs.langmuir.1c00417

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DOI： 10.1103/physreve.103.042502

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DOI： 10.1039/d0cp05826b

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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

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DOI： 10.1246/cl.200323

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DOI： 10.1021/acs.biomac.0c01095

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DOI： 10.1126/sciadv.aax9301

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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

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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

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Ionic Conductivity in Ionic Liquid Nano Thin Films
PMID: 30199622

DOI： 10.1021/acsnano.8b06386

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DOI： 10.1246/cl.180450

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DOI： 10.1016/j.carbon.2018.03.034

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DOI： 10.1016/j.jcat.2018.03.017

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DOI： 10.1038/s41428-018-0067-1

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DOI： 10.1021/acs.macromol.8b00124

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DOI： 10.1021/acsami.7b07551

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DOI： 10.1021/acsami.7b07737

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DOI： 10.1021/acs.macromol.6b02613

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DOI： 10.1038/srep46394

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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

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DOI： 10.1103/PhysRevE.94.042611

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DOI： 10.1088/0965-0393/24/5/055006

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DOI： 10.1021/acsami.5b11910

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DOI： 10.1039/c5cp06515a

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DOI： 10.1021/acs.jpcc.5b08561

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DOI： 10.1103/PhysRevE.92.062713

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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

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DOI： 10.1039/c5ta05575j

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DOI： 10.1016/j.chemphys.2015.08.007

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DOI： 10.1021/acs.jpcc.5b01370

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DOI： 10.1149/06801.3187ecst

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DOI： 10.1038/srep09052

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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

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DOI： 10.1021/jp5015252

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DOI： 10.1039/c4ra04065a

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DOI： 10.1021/jp503331e

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DOI： 10.1021/jp412461q

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DOI： 10.1063/1.4869515

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DOI： 10.1149/05701.2459ecst

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

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DOI： 10.1021/jp4021504

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DOI： 10.1021/jp310920d

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DOI： 10.7567/JJAP.52.026502

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DOI： 10.1021/jp3002542

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DOI： 10.1039/c2fd00125j

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DOI： 10.1103/PhysRevE.84.021924

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DOI： 10.1103/PhysRevE.82.031909

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DOI： 10.1016/j.ultramic.2010.02.032

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DOI： 10.1016/j.cplett.2008.06.068

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DOI： 10.1063/1.2759925

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Conformational Hysteresis on A Giant DNA Molecule

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

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Language：Japanese  

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.

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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.

Language：English  

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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

Language：Japanese  

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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.

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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.

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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.

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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.

Language：Japanese  

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Type：Competition, symposium, etc. 

Type：Competition, symposium, etc.