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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.porgcoat.2021.106654

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.polymertesting.2021.107123

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.polymdegradstab.2020.109242

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.polymer.2019.122035

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.polymdegradstab.2019.02.007

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1295/koron.2017-0082

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/fld.5258

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掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal for Numerical Methods in Fluids  

We develop a novel Moving Particle Simulation (MPS) method to reproduce the motion of fibers floating in sheared liquids accurately. In conventional MPS schemes, if a fiber suspended in a liquid is represented by a one-dimensional array of MPS particles, it is entirely aligned to the flow direction due to the lack of shear stress difference between fiber–liquid interfaces. To address this problem, we employ the micropolar fluid model to introduce rotational degrees of freedom into the MPS particles. The translational motion of liquid and solid particles and the rotation of solid particles are calculated with the explicit MPS algorithm. The fiber is modeled as an array of micropolar fluid particles bonded with stretching, bending and torsional potentials. The motion of a single rigid fiber is simulated in a three-dimensional shear flow generated between two moving solid walls. We show that the proposed method is capable of reproducing the fiber motion predicted by Jeffery's theory which is different from the conventional MPS simulations.

DOI： 10.1002/fld.5235

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arXiv

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その他リンク： http://arxiv.org/pdf/2301.03818v1

担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Construction and Building Materials  

This study proposes applying the concept of fluctuating diffusivity (FD) to the diffusion of gas molecules in cementitious materials, mainly through a two-state fluctuating diffusivity (2SFD) model. The 2SFD model was utilized to investigate oxygen diffusion in cement pastes. This analysis provides a reasonable description of the oxygen diffusion coefficient in cement pastes and suggests the presence of non-Gaussian diffusion, which is attributed to the heterogeneous microstructure. The presence of non-Gaussianity in the probability density of the displacement of the molecule, characterized by heavier tails than those of the Gaussian distribution, may significantly impact the durability of concrete structures.

DOI： 10.1016/j.conbuildmat.2023.133411

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Macromolecules  

The influence of node functionality (f) on the fracture of polymer networks remains unclear. While many studies have focused on multifunctional nodes with f > 4, recent research suggests that networks with f = 3 exhibit superior fracture properties compared to those with f = 4. To clarify this discrepancy, we conducted phantom chain simulations for star-polymer networks varying f between 3 and 8. Our simulations utilized equimolar binary mixtures of star branch prepolymers with a uniform arm length. We employed a Brownian dynamics scheme to equilibrate the sols and induce gelation through end-linking reactions. We prevented the formation of odd-order loops algorithmically, owing to the binary reaction and second-order loops. We stored network structures at various conversion ratios (φc) and minimized energy to reduce computation costs induced by structural relaxation. We subjected the networks to stretching until fracture to determine stress and strain at break and work for fractures, ϵb, σb, and Wb. These fracture characteristics are highly dependent on φc for networks with a small f but relatively insensitive for those with a large f. Thus, the networks with small f exhibit greater fracture properties than those with large f at high φc, whereas the opposite relationship occurs at low φc. We analyzed ϵb, σb, and Wb concerning cycle rank ξ and broken strand fraction φbb. We found that ϵb, σb/φbb, and Wb/φbb monotonically decrease with increasing ξ, and the data for various f and φc superpose with each other to draw master curves. These results imply that the mechanical superiority of the networks with small f comes from their smaller ξ that gives higher ϵb, σb/φbb, and Wb/φbb than the networks with large f.

DOI： 10.1021/acs.macromol.3c01291

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arXiv

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その他リンク： http://arxiv.org/pdf/2307.09832v1

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nihon Reoroji Gakkaishi  

In the multi-chain slip-spring, the dynamics of Rouse chains connected by virtual springs called slip-springs that hop along the chain are considered. Although this approach has been proven to reproduce entangled polymer dynamics efficiently, the settings of the artificially introduced slip-springs should be carefully examined. In this study, we discussed the effect of the slip-spring degeneracy by limiting the number of anchored slip-springs on each Rouse bead to zero and one. According to the altered slip-spring statistics, we derived the compensation potential to eliminate the artifact of slip-springs on the chain statistics. With this potential, we performed numerical simulations. The results demonstrated that although we reasonably retain the Gaussian chain statistics, the dynamics deviate from the established entangled polymer dynamics because of the significant slow-down in the chain motion induced by the correlation between different slip-springs. The observed deceleration can be explained by the fact that the movement of slip-springs can be cast into an asymmetric exclusion process.

DOI： 10.1678/rheology.51.211

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Polymer Journal  

Two-dimensional sheet-shaped poly(methyl methacrylate) (2d-PMMA) with crosslinking only in the two-dimensional direction was synthesized via planar polymerization of MMA monomer in montmorillonite (MMT) nanolayers by using γ-ray irradiation, and the samples obtained were characterized. Size-exclusion chromatography with a multi-angle light scattering (SEC-MALS) measurements of the obtained sample showed bimodal peaks: a main peak with a longer elution time and an apparent molecular weight M w,app and radius of gyration R g in tetrahydrofuran (THF) similar to those for linear PMMA samples, and a subpeak with a shorter elution time and M w,app and R g evidently lower than those for the linear PMMA samples. This result indicated that polymers with moderate branching and crosslinking were contained in the subpeak. Atomic force microscopy (AFM) observation of the sample showed the presence of sheet-shaped molecules with a height of ca. 0.6 nm, corresponding to the thickness of one MMA monomer, and a width of several to several tens of nanometers, showing a broad distribution in molecular width. The subpeak portion was isolated via SEC fractionation, and its AFM observation showed thin circular disk-shaped molecules with relatively uniform size (i.e., a width of several tens of nanometers). However, in these molecules, two types of molecular heights (i.e., 0.6 and 1.2 nm) were identified. This result indicated that MMA monomers were filled as two layers within one MMT interlayer, and the polymerization reaction proceeded in that state. The similarity in the molecular size of 2d-PMMA observed via AFM and SEC-MALS was confirmed. These results demonstrated that the desired sheet-shaped polymers were obtained through the above synthesis and fractionation process.

DOI： 10.1038/s41428-023-00795-4

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その他リンク： https://www.nature.com/articles/s41428-023-00795-4

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review E  

Rod-shaped particles embedded in certain matrices have been reported to exhibit an increase in their center of mass diffusivity upon increasing the matrix density. This increase has been considered to be caused by a kinetic constraint in analogy with tube models. We investigate a mobile rodlike particle in a sea of immobile point obstacles using a kinetic Monte Carlo scheme equipped with a Markovian process, that generates gaslike collision statistics, so that such kinetic constraints do essentially not exist. Even in such a system, provided the particle's aspect ratio exceeds a threshold value of about 24, the unusual increase in the rod diffusivity emerges. This result implies that the kinetic constraint is not a necessary condition for the increase in the diffusivity.

DOI： 10.1103/PhysRevE.107.044604

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arXiv

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その他リンク： http://arxiv.org/pdf/2301.02394v2

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Macromolecules  

Effects of branch functionality on mechanical properties of polymer networks are yet to be fully elucidated, although multi-functional approaches have been mainly attempted. For instance, Fujiyabu et al. [Sci. Adv. 2022, 8, abk0010] recently reported that polymer networks made from tri-branch prepolymers exhibit superior mechanical properties to tetra-branch analogues. Although they attribute the difference to stretch-induced crystallization observed in tri-branch poly (ethylene glycol) networks, the mechanism still needs to be clarified. In this study, we performed coarse-grained molecular simulations to extract the effect of branch functionality. The prepolymers were replaced by bead-spring phantom chains, and gelation was simulated by a Brownian dynamics scheme. We subjected the resultant networks to energy minimization and uniaxial stretch by introducing breakage for elongated segments. In the stress-strain relation thus obtained, stress and strain at the break were larger for tri-branch networks than that for tetra-branch analogues, consistent with the experiment. The superiority of tri-branch networks is observed in a wide range of the conversion ratio in gelation, molecular weights of prepolymers, and polymer concentrations. The result implies that the mechanical superiority of tri-branch networks to tetra-branch ones is due to a fundamental structural difference generated during gelation.

DOI： 10.1021/acs.macromol.3c00047

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review E  

Diffusivity in some soft matter and biological systems changes with time, called the fluctuating diffusivity. In this work, we propose a novel origin for fluctuating diffusivity based on stochastic simulations of binary gas mixtures. In this system, the fraction of one component is significantly small, and the mass of the minor component molecule is different from that of the major component. The minor component exhibits fluctuating diffusivity when its mass is sufficiently smaller than that of the major component. We elucidate that this fluctuating diffusivity is caused by the time scale separation between the relaxation of the velocity direction and the speed of the minor component molecule.

DOI： 10.1103/PhysRevE.107.014605

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その他リンク： http://arxiv.org/pdf/2207.05424v2

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nihon Reoroji Gakkaishi  

We derive the stress tensor of a rigid dumbbell by using the virtual work method. In the virtual work method, we virtually apply a small deformation to the system, and relate the change of the energy to the work done by the stress tensor. A rigid dumbbell consists of two particles connected by a rigid bond of which length is constant (the rigid constraint). The energy of the rigid dumbbell consists only on the kinetic energy. Also, only the deformations which do not violate the rigid constraint are allowed. Thus we need the dynamic equations which are consistent with the rigid constraint to apply the virtual deformation. We rewrite the dynamic equations for the underdamped SLLOD-type dynamic equations into the forms which are consistent with the rigid constraint. Then we apply the virtual deformation to a rigid dumbbell based on the obtained dynamic equations. We derive the stress tensor for the rigid dumbbell model from the change of the kinetic energy. Finally, we take the overdamped limit and derive the stress tensor and the dynamic equation for the overdamped rigid dumbbell. We show that the Green-Kubo type linear response formula can be reproduced by combining the stress tensor and the dynamic equation at the overdamped limit.

DOI： 10.1678/rheology.50.313

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arXiv

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その他リンク： http://arxiv.org/pdf/2205.09374v1

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/polym13050820

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：CIMNE  

DOI： 10.23967/dbmc.2020.087

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本塗装技術協会  

CiNii Books

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掲載種別：研究論文（国際会議プロシーディングス）  

Polyurethane composite coatings are frequently applied to strengthen the barrier properties of various construction materials such as wood, metal and concrete. The changes of color and glossiness of the composite coatings for building materials proceeds more slowly than that of polyurethane because of containing fillers and several types of additives. However, the most critical barrier properties have not been studied directly based on the difference from the degradation mechanism of polyurethane coatings. Additionally, the difference in thermal and UV degradation mechanisms of coatings is not clear in the existing studies dealing with conventional accelerated weathering tests and outdoor exposure tests. Therefore, the behavior of the filler contained in the coatings was observed using an oven to accelerate thermal degradation. The chemical analysis of the coating surface by XPS and the analysis of the images and elemental mappings by SEM-EDS were carried out, and the mechanism of degradation progress was investigated. In addition, the temperature dependency of the degradation was studied in changing the heating temperature. It was suggested that polymer and fillers interact in promoting mass transfer at the same time as the thermal degradation reaction consequently.

DOI： 10.23967/dbmc.2020.100

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担当区分：筆頭著者   記述言語：日本語   掲載種別：学位論文（修士）  

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担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本塗装技術協会  

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記述言語：日本語   出版者・発行元：日本建築学会  

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記述言語：日本語   出版者・発行元：日本建築学会  

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J-GLOBAL

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記述言語：日本語   出版者・発行元：日本建築学会  

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記述言語：日本語   出版者・発行元：日本建築学会  

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記述言語：日本語   出版者・発行元：日本建築学会  

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