研究者詳細 - 畝山　多加志

論文 - 畝山　多加志

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

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

Polymer Journal 2023年5月

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

Web of Science

Scopus

Increase in rod diffusivity emerges even in Markovian nature 査読有り国際共著

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

Physical Review E 107 巻 ( 4 ) 頁： 044604 2023年4月

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

Scopus

PubMed

Fluctuating diffusivity emerges even in binary gas mixtures 査読有り

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

Physical Review E 107 巻 ( 1 ) 頁： 014605-1 - 014605-9 2023年1月

担当区分：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：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 査読有り

2023年

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

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

Molecular Simulation 2023年

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：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 査読有り

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

Nihon Reoroji Gakkaishi 50 巻 ( 4 ) 頁： 305 - 312 2022年9月

Stress Tensor of Single Rigid Dumbbell by Virtual Work Method 査読有り

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

Nihon Reoroji Gakkaishi 50 巻 ( 4 ) 頁： 313 - 322 2022年9月

過渡ポテンシャルを用いたソフトマテリアルの粗視化モデリング

畝山多加志

材料 71 巻 ( 8 ) 頁： 666 - 671 2022年8月

担当区分：筆頭著者,　最終著者,　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：一般社団法人日本物理学会

物性の研究ではマクロスケールの（巨視的な）物性について測定や解析が行われることが多い．マクロスケールの物質の示す複雑な緩和や応答も元をたどれば究極的にはミクロスケールの（微視的な）分子や原子の構造に還元できると期待される．これは物理（特に統計力学）の考え方としては標準的なものであろう．ソフトマターのように構成要素が複雑な場合には，ミクロスケールとマクロスケールの中間であるメソスケールにおいて特徴的な構造や運動をもつことがある．この場合もやはりメソスケールの挙動は究極的にはミクロスケールに還元できると考えられる．原理的には分子や原子の初期状態の位置と運動量がわかれば系の時間発展は一意に決まるのだから，メソスケールだろうとマクロスケールだろうとミクロスケールの情報からすべて計算が可能なように思える．もちろん，初期状態を完全に知ることはできないし，カオス的な振る舞いもあるため状況はそこまで単純ではない．メソスケールの運動や緩和，あるいはメソスケールの情報を強く反映するマクロスケールの物性を理解するには，メソスケールの運動を直接的に記述し解析することが望ましい．これはミクロスケールの情報のうち興味ある一部の情報（着目する粒子の位置や運動量）のみを取り出す粗視化とよばれる手法を用いて実現できる．粗視化によって消える自由度の効果は系統的に取り込め，未知の初期状態の影響はランダムな揺動力という形で運動方程式中に現れる．このランダムな揺動力がBrown運動の起源となり，粒子の運動の軌跡は不規則な形状を呈することになる．さらに，粒子の感じるポテンシャルや時間遅れの効果等を取り込むことで，メソスケールの運動の一般的記述が可能になるとされている．ところが，このような手法で十分に一般的なメソスケールの運動を記述可能かというと，実はそうではない．既存の手法で記述不可能な対象が少なからず存在するのである．例えば，高分子の運動は分子同士が互いにすり抜けられないという動的な拘束のために単純な形では記述できない．近年，そのようなある種の特殊なBrown運動の記述について，新しい視点からのモデル化や理解が進展しつつある．メソスケールの系を記述する際に通常着目する自由度である位置や運動量に加えて，拡散係数やポテンシャルといった量も自由度として考慮するというものである．従来の方法では，拡散係数やポテンシャルは環境の効果を平均化したものであり，平均値からのずれがランダムな揺動力として取り扱われていた．これに対して，新しい方法では，拡散係数やポテンシャル自体が時々刻々と変化する環境の影響を受けてランダムに変化する量であるとする．一見，ランダムに変化する部分が変わっただけでさほどの影響がないように思えるかもしれないが，ゆらぐ拡散係数やポテンシャルを使うことで従来の方法とは定性的に異なる運動を記述することができる．ゆらぐ拡散係数やポテンシャルを用いた新しい方法は新しい運動方程式のクラスを形成しているものと考えられる．新しい方法はソフトマターをはじめとしたさまざまな系に適用できるものと期待される．例えば，高分子の動的な拘束を表現するために各論的・現象論的にさまざまな運動モデルが提案されているが，これらをゆらぐ拡散係数やポテンシャルを使った枠組みで統一的に解釈し直すことができる．また，過冷却液体中の分子の示す一時的にトラップされるような運動も，新しい方法を用いることで単純な形で記述することができる．

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

Linear Response Theory of Scale-Dependent Viscoelasticity for Overdamped Brownian Particle Systems 査読有り

Takashi Uneyama

Nihon Reoroji Gakkaishi 50 巻 ( 3 ) 頁： 275 - 286 2022年6月

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

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

Soft matter 2022年6月

Application of projection operator method to coarse-grained dynamics with transient potential 査読有り

Uneyama T.

Physical Review E 105 巻 ( 4 ) 2022年4月

担当区分：筆頭著者,　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：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. 査読有り

Journal of Physical Chemistry B 2022年3月

Nonlinear Shear and Elongational Rheology of Poly(propylene carbonate) 査読有り

Lixin Yang, Takashi Uneyama, Yuichi Masubuchi, Yuya Doi

Nihon Reoroji Gakkaishi 50 巻 ( 1 ) 頁： 127 - 135 2022年2月

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

Masubuchi Y, Yang L, Uneyama T, Doi Y

Polymers 14 巻 ( 4 ) 2022年2月

高分子の統計力学的取り扱い

畝山多加志

高分子 71 巻頁： 614 - 616 2022年

Radial Distribution Functions of Entanglements in Primitive Chain Network Simulations 査読有り

Masubuchi Yuichi, Kida Takumitsu, Doi Yuya, Uneyama Takashi

49 巻 ( 5 ) 頁： 337 - 345 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

複雑な運動の新しい見方――時間に依存してゆらぐポテンシャルと拡散係数

畝山多加志

日本物理学会誌 76 巻 ( 10 ) 頁： 663 - 668 2021年10月

担当区分：筆頭著者,　最終著者,　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：一般社団法人日本物理学会

DOI： 10.11316/butsuri.76.10_663

Linear Rheological Properties of Poly(Propylene Carbonate) with Different Molecular Weights 査読有り

Lixin Yang, Takashi Uneyama, Yuichi Masubuchi, Yuya Doi

Nihon Reoroji Gakkaishi 49 巻 ( 4 ) 頁： 267 - 274 2021年9月

Rheological properties of linear and short-chain branched polyethylene with nearly monodispersed molecular weight distribution 査読有り

Kida T., Doi Y., Tanaka R., Uneyama T., Shiono T., Masubuchi Y.

Rheologica Acta 60 巻 ( 9 ) 頁： 511 - 519 2021年9月

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：Rheologica Acta

We synthesized model polyethylene (PE) samples with nearly monodispersed molecular weight distribution and different fractions of short-chain branches to investigate the influences of the branch structure on the rheological properties. The activation energy of the flow process showed linear relations with the weight fractions of comonomer and the short-chain branch. These results suggest that the friction of the chain motion is dominated by the amount of the short-chain branch. The zero-shear viscosity showed a power law to Mw with an exponent of about 3.3 for all linear and branched PEs. The branched PEs showed large entanglement molecular weights compared with the linear PEs because the introduction of the short-chain branches results in the increase of the average molecular weight per backbone unit. Moreover, the introduction of the short-chain branches has no influence on the strain-hardening under an extensional elongation process, indicating that the short-chain branches only affect the friction.

DOI： 10.1007/s00397-021-01286-0

Scopus

Linear Viscoelasticity of Dumbbells Interacting via Gaussian Soft-Core Potential 査読有り

Takashi Uneyama

Nihon Reoroji Gakkaishi 49 巻 ( 2 ) 頁： 61 - 71 2021年4月

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