Faculty Profiles - UNEYAMA Takashi

Papers - UNEYAMA Takashi

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A Multi-Chain Slip-Spring Model without the Slip-Spring Degeneracy Reviewed

Masubuchi Yuichi, Doi Yuya, Ishida Takato, Uneyama Takashi

Nihon Reoroji Gakkaishi Vol. 51 ( 4 ) page： 211 - 217 2023.9

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：The Society of Rheology, Japan

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

CiNii Research

Estimating Relaxation Times from a Single Trajectory Reviewed

Takuma Akimoto, Eiji Yamamoto, and Takashi Uneyama

Journal of Physical Society of Japan Vol. 92 ( 7 ) page： 074005-1 - 074005-8 2023.6

Preparation and characterization of two-dimensional sheet-shaped poly(methyl methacrylate) synthesized via gamma-ray polymerization in nanoclay template Reviewed

Doi Yuya, Hara Mitsuo, Seki Takahiro, Takano Atsushi, Ishida Takato, Uneyama Takashi, Masubuchi Yuichi

Polymer Journal 2023.5

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

Scopus

Increase in rod diffusivity emerges even in Markovian nature Reviewed International coauthorship

Nakai F, Kröger M, Ishida T, Uneyama T, Doi Y, Masubuchi Y

Physical Review E Vol. 107 ( 4 ) page： 044604 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Scopus

PubMed

Fluctuating diffusivity emerges even in binary gas mixtures Reviewed

Nakai F., Masubuchi Y., Doi Y., Ishida T., Uneyama T.

Physical Review E Vol. 107 ( 1 ) page： 014605-1 - 014605-9 2023.1

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：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

Scopus

Phantom Chain Simulations for the Fracture of Energy-Minimized Tetra- and Tri-Branched Networks Reviewed

2023

Effects of attractive inter-particle interaction on cross-transport coefficient between mass and heat in binary fluids Reviewed

Oishi T., Doi Y., Masubuchi Y., Uneyama T.

Molecular Simulation 2023

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Molecular Simulation

In some binary fluids, mass transport is observed under a temperature gradient. This phenomenon is called the Soret effect. In this study, we discuss the influence of inter-particle interaction. We considered equimolar binary Lennard–Jones fluids with a mass contrast, whereas the interaction was common for all the particle pairs with various cut-off lengths. We performed molecular dynamics simulations of such fluids under equilibrium to obtain the cross-transport coefficients (Formula presented.) between the fluxes of mass and heat. The simulation revealed that this quantity strongly depends on the cut-off length. Further, we decomposed the heat flux into kinetic and potential contributions and calculated the cross-correlations between decomposed fluxes and the mass flux. The result indicates that the potential contribution dominates (Formula presented.), implying that the Soret coefficient is altered by the inter-particle interaction.

DOI： 10.1080/08927022.2023.2268730

Scopus

Primitive Chain Network Simulations for Shear Rheology of Poly (propylene carbonate) Melts Reviewed

Y. Masubuchi and L. Yang and T. Uneyama and Y. Doi

Nihon Reoroji Gakkaishi Vol. 50 ( 4 ) page： 305 - 312 2022.9

Stress Tensor of Single Rigid Dumbbell by Virtual Work Method Reviewed

T. Uneyama and T. Oishi and T. Ishida and Y. Doi and Y. Masubu chi

Nihon Reoroji Gakkaishi Vol. 50 ( 4 ) page： 313 - 322 2022.9

Coarse-Grained Modeling of Soft Materials by using Transient Potentials

Uneyama Takashi

Journal of the Society of Materials Science, Japan Vol. 71 ( 8 ) page： 666 - 671 2022.8

Authorship：Lead author,　Last author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Physical Society of Japan

Soft matters often exhibit complex random motions (Brownian motions) at the mesoscopic scale. Due to the internal degrees of freedom and interaction, the mesoscopic dynamics can be rather complex. To describe such complex dynamics, we need to reduce the degrees of freedom of target systems (the coarse-graining). Conventionally, the projection operator method and the generalized Langevin equation have been utilized to describe such dynamics. Recently, other coarse-graining methods have been proposed where the diffusion coefficients and potentials are treated as time-dependent and fluctuating quantities. The fluctuating diffusion coefficients and potentials enable us to express complex random dynamics of soft matters with relatively simple dynamic equation models. We show basic concepts and some applications of fluctuating diffusion coefficients and potentials.

DOI： https://doi.org/10.2472/jsms.71.666

Linear Response Theory of Scale-Dependent Viscoelasticity for Overdamped Brownian Particle Systems Reviewed

Takashi Uneyama

Nihon Reoroji Gakkaishi Vol. 50 ( 3 ) page： 275 - 286 2022.6

Brownian simulations for tetra-gel-type phantom networks composed of prepolymers with bidisperse arm length. Reviewed

Masubuchi Y, Yamazaki R, Doi Y, Uneyama T, Sakumichi N, Sakai T

Soft matter 2022.6

Application of projection operator method to coarse-grained dynamics with transient potential Reviewed

Uneyama T.

Physical Review E Vol. 105 ( 4 ) 2022.4

Authorship：Lead author,　Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Review E

We show that the coarse-grained dynamics model with the time-dependent and fluctuating potential (transient potential) can be derived from the microscopic Hamiltonian dynamics. The concept of the transient potential was first introduced rather phenomenologically, and its relation to the underlying microscopic dynamics has not been clarified yet. This is in contrast to the generalized Langevin equation, the relation of which to the microscopic dynamics is well-established. In this work, we show that the dynamic equations with the transient potential can be derived for the coupled oscillator model, without any approximations. It is known that the dynamics of the coupled oscillator model can be exactly described by the generalized Langevin-type equations. This fact implies that the dynamic equations with the transient potential can be utilized as a coarse-grained dynamics model in a similar way to the generalized Langevin equation. Then we show that the dynamic equations for the transient potential can also be formally derived for the microscopic Hamiltonian dynamics, without any approximations. We use the projection operator method for the coarse-grained variables and transient potential. The dynamic equations for the coarse-grained positions and momenta are similar to those in the Hamiltonian dynamics, but the interaction potential is replaced by the transient potential. The dynamic equation for the transient potential is the generalized Langevin equation with the memory effect. Our result justifies the use of the transient potential to describe the coarse-grained dynamics. We propose several approximations to obtain the simplified dynamics model. We show that, under several approximations, the dynamic equation for the transient potential reduces to the relatively simple Markovian dynamic equation for the potential parameters. We also show that with several additional approximations, the approximate dynamics model further reduces to the Markovian Langevin-type equations with the transient potential.

DOI： 10.1103/PhysRevE.105.044117

Scopus

Effects of Slip-Spring Parameters and Rouse Bead Density on Polymer Dynamics in Multichain Slip-Spring Simulations. Reviewed

Journal of Physical Chemistry B 2022.3

Nonlinear Shear and Elongational Rheology of Poly(propylene carbonate) Reviewed

Lixin Yang, Takashi Uneyama, Yuichi Masubuchi, Yuya Doi

Nihon Reoroji Gakkaishi Vol. 50 ( 1 ) page： 127 - 135 2022.2

Analysis of Elongational Viscosity of Entangled Poly (Propylene Carbonate) Melts by Primitive Chain Network Simulations. Reviewed

Masubuchi Y, Yang L, Uneyama T, Doi Y

Polymers Vol. 14 ( 4 ) 2022.2

高分子の統計力学的取り扱い

畝山多加志

高分子 Vol. 71 page： 614 - 616 2022

Radial Distribution Functions of Entanglements in Primitive Chain Network Simulations Reviewed

Masubuchi Yuichi, Kida Takumitsu, Doi Yuya, Uneyama Takashi

Vol. 49 ( 5 ) page： 337 - 345 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：一般社団法人日本レオロジー学会

Although the entanglement network among polymers has been widely investigated, the spatial distribution of entanglement nodes has been rarely discussed. In this study, we obtained the radial distribution functions (RDFs) for the entanglement nodes from the snapshots of multi-chain slip-link simulations. The model employed in this study is the primitive chain network (PCN) model, which has been validated to reproduce the entangled polymer dynamics semi-quantitatively. The statistics of captured entanglement networks were compared to those reported for the primitive path network extracted by the CReTA procedure from the full-atomistic molecular model of a polyethylene melt. In the range of distance longer than the average strand length, the network structure from PCN does not show any structural correlation, and the intra-chain correlation is close to that for Gaussian chains with non-interacting slip-links. These features are consistent with the CReTA network and the conventional assumptions made for single-chain models. Meanwhile, in the short-range, the structural correlation in PCN is much weaker than that in CReTA. This discrepancy is because the short-range structure in PCN is realized as a result of imposed fluctuations, whereas it is determined by the minimization of the primitive path in CReTA.

DOI： 10.1678/rheology.49.337

A New Viewpoint for Complex Dynamics―Time-Dependent and Fluctuating Potentials and Diffusion Coefficients

Uneyama Takashi

Butsuri Vol. 76 ( 10 ) page： 663 - 668 2021.10

Authorship：Lead author,　Last author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Physical Society of Japan

DOI： 10.11316/butsuri.76.10_663

Linear Rheological Properties of Poly(Propylene Carbonate) with Different Molecular Weights Reviewed

Lixin Yang, Takashi Uneyama, Yuichi Masubuchi, Yuya Doi

Nihon Reoroji Gakkaishi Vol. 49 ( 4 ) page： 267 - 274 2021.9

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Papers - UNEYAMA Takashi