研究者詳細 - 増渕　雄一

Modeling for Heterogeneous Oxidative Aging of Polymers Using Coarse-Grained Molecular Dynamics 査読有り国際誌 Open Access

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

Macromolecules 56 巻 ( 21 ) 頁： 8474 - 8483 2023年11月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Macromolecules

This study presents a coarse-grained molecular dynamics simulation model to investigate the process of oxidative aging in polymers. The chemical aging effect is attributed to the autoxidation mechanism, which is initiated by radicals, leading to the chain scission and cross-linking of polymer chains. In this study, we integrate a thermal oxidation kinetic model in the oxygen excess regime into the Kremer-Grest model, thereby enabling a reactive coarse-grained molecular dynamics simulation to capture the process of oxidative degradation. Our simulation reveals that when the time scale of the characteristic reaction step of oxidative degradation is shorter than the longest relaxation time of polymer chains, the scission sites exhibit spatial heterogeneity. This innovative simulation model possesses the potential to enhance our comprehension of polymer aging phenomena, thus making noteworthy contributions to the realm of polymer science and degradation chemistry.

DOI： 10.1021/acs.macromol.3c01708

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

Oishi, T; Doi, Y; Masubuchi, Y; Uneyama, T

MOLECULAR SIMULATION 2023年10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：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

A Multi-Chain Slip-Spring Model without the Slip-Spring Degeneracy 査読有り国際誌 Open Access

Masubuchi, Y; Doi, Y; Ishida, T; Uneyama, T

NIHON REOROJI GAKKAISHI 51 巻 ( 4 ) 頁： 211 - 217 2023年10月

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）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

Extension of moving particle simulation by introducing rotational degrees of freedom for dilute fiber suspensions 査読有り国際誌

Enomoto K., Ishida T., Doi Y., Uneyama T., Masubuchi Y.

International Journal for Numerical Methods in Fluids 96 巻頁： 125 - 137 2023年9月

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：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

Phantom-Chain Simulations for the Effect of Node Functionality on the Fracture of Star-Polymer Networks 査読有り国際誌 Open Access

Masubuchi, Y; Doi, Y; Ishida, T; Sakumichi, N; Sakai, T; Mayumi, K; Satoh, K; Uneyama, T

MACROMOLECULES 56 巻 ( 23 ) 頁： 9359 - 9367 2023年9月

Preparation and characterization of two-dimensional sheet-shaped poly(methyl methacrylate) synthesized via γ-ray polymerization in nanoclay template 招待有り査読有り国際誌 Open Access

Doi Y., Hara M., Seki T., Takano A., Ishida T., Uneyama T., Masubuchi Y.

Polymer Journal 55 巻 ( 9 ) 頁： 957 - 965 2023年5月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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

Undershoots in shear startup of entangled linear polymer blends 招待有り査読有り国際共著国際誌 Open Access

Parisi Daniele, Vereroudakis Emmanouil, Masubuchi Yuichi, Ianniruberto Giovanni, Marrucci Giuseppe, Vlassopoulos Dimitris

JOURNAL OF NON-NEWTONIAN FLUID MECHANICS 315 巻 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：Journal of Non-Newtonian Fluid Mechanics

We revisit the transient response of entangled polymers in shear startup. Evidence from state-of-the-art experiments, modeling and simulations suggests the presence in fast flows of a weak (albeit unambiguous) undershoot, following the overshoot, i.e., while approaching the steady state. Recent sliplink simulations confirmed that the undershoot is not due to slip at the wall, and hence it is intrinsic to polymer rheology. Here, we further examine some features of the undershoot by blending two entangled homopolymers at different compositions. Since blending affects the distribution of relaxation times, it is here shown to also affect the undershoot, probably by broadening the tumbling-time distribution. Indeed, by appropriately modifying our tube-based model, that invokes tumbling to account for the undershoot, and (in parallel) by using simulations, we show how the undershoot depends on the blend composition. We map the experimental results into a diagram of terminal relaxation time versus composition, which identifies regimes where the undershoot is present. Blending is therefore proposed as a molecular mechanism to tailor the shear stress growth function signal, particularly the undershoot.

DOI： 10.1016/j.jnnfm.2023.105028

Primitive chain network simulations of the nonlinear rheology of polystyrene melts: Friction reduction and fluctuation-dissipation theorem 招待有り査読有り国際共著国際誌 Open Access

Masubuchi Yuichi, Ianniruberto Giovanni, Wagner Manfred, Marrucci Giuseppe

JOURNAL OF NON-NEWTONIAN FLUID MECHANICS 315 巻 2023年5月

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）出版者・発行元：Journal of Non-Newtonian Fluid Mechanics

Description of the elongational rheology of concentrated polymers appears to require that in fast flows the friction coefficient decreases with respect to its equilibrium value. However, the proposed models typically maintain the validity of the fluctuation-dissipation theorem (FDT) out of equilibrium. On the other hand, FDT is routed in local equilibrium, the latter being clearly violated by the flow-induced monomer coalignment that induces friction change. A recent analysis by Watanabe et al. [Macromolecules, 54, 3700 (2021)] of unentangled polystyrene (PS) melts, based on a nonlinear extension of the Rouse model, indicates that FDT is indeed violated in fast flows. According to their analysis, the Brownian force intensity remains almost independent of the flow rate, even though the friction coefficient drastically decreases. A different violation of FDT is shown by previous nonequilibrium molecular dynamics simulations of PS oligomers [Ianniruberto et al., Macromolecules, 45, 8058 (2012)] where the diffusion coefficient grows more than the inverse friction coefficient. In this paper, Brownian simulations using a multi-chain sliplink model (the so-called primitive chain network model) are reported for two monodisperse entangled PS melts, for which nonlinear shear and elongational data were published. Two different friction reduction models are examined, and the effect of switching FDT on and off is tested. Results demonstrate that, irrespective of FDT, both friction models can reasonably well reproduce the behavior shown by the data. This result lends support to models that retain FDT since its violation appears not to significantly affect predictions of nonlinear rheology.

DOI： 10.1016/j.jnnfm.2023.105019

Increase in rod diffusivity emerges even in Markovian nature 査読有り国際共著国際誌 Open Access

Nakai Fumiaki, Kroger Martin, Ishida Takato, Uneyama Takashi, Doi Yuya, Masubuchi Yuichi

PHYSICAL REVIEW E 107 巻 ( 4 ) 2023年4月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review E

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

Phantom Chain Simulations for the Fracture of Energy-Minimized Tetra- and Tri-Branched Networks 査読有り国際誌

Masubuchi Yuichi, Doi Yuya, Ishida Takato, Sakumichi Naoyuki, Sakai Takamasa, Mayumi Koichi, Uneyama Takashi

MACROMOLECULES 2023年2月

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）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

Tube Survival Fraction in Primitive Chain Network Simulations 査読有り国際誌 Open Access

Masubuchi Yuichi

Nihon Reoroji Gakkaishi 51 巻 ( 1 ) 頁： 19 - 24 2023年2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：The Society of Rheology, Japan

In the framework of the tube model, the survival fraction of dilated tube, φʹ(t), is essential since the relaxation of the entire system is described according to this quantity. However, a method to define it in multi-chain simulations has yet to be considered. In this study, primitive chain network simulations were performed, and a few structural quantities were discussed as possible candidates for use as φʹ(t). Before analysis, the simulation was evaluated against literature data for linear polyisoprene melts, and quantitative agreement was obtained for viscoelastic and dielectric relaxations. Afterward, the end-to-end relaxation function was compared to survival probability of the slip link φs(t) and the ratio of monomers between the most distant surviving slip link pair to the total number of monomers ns(t)/nt. The result implies that ns(t)/nt is comparable to φʹ(t). Comparison to atomistic molecular dynamics (MD) simulations for polyethylene showed similar results, implying that φʹ(t) can be obtained even in MD simulations if the surviving entanglement points can be specified.

DOI： 10.1678/rheology.51.19

CiNii Research

Fluctuating diffusivity emerges even in binary gas mixtures 査読有り国際誌 Open Access

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

Physical Review E 107 巻 ( 1 ) 2023年1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

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

Elongational viscosity of poly(propylene carbonate) melts: tube-based modelling and primitive chain network simulations 査読有り国際共著国際誌 Open Access

Wagner Manfred H., Narimissa Esmaeil, Masubuchi Yuichi

RHEOLOGICA ACTA 62 巻 ( 1 ) 頁： 1 - 14 2023年1月

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：Rheologica Acta

In fast elongational flows, linear polymer melts exhibit a monotonic decrease of the viscosity with increasing strain rate, even beyond the contraction rate of the polymer defined by the Rouse time. We consider two possible explanations of this phenomenon: (a) the reduction of monomeric friction and (b) the reduction of the tube diameter with increasing deformation leading to an Enhanced Relaxation of Stretch (ERS) on smaller length scales. (Masubuchi et al. (2022) reported Primitive Chain Network (PCN) simulations using an empirical friction reduction model depending on segmental orientation and could reproduce the elongational viscosity data of three poly(propylene carbonate) melts and a polystyrene melt. Here, we show that the mesoscopic tube-based ESR model (Wagner and Narimissa 2021) provides quantitative agreement with the same data set based exclusively on the linear-viscoelastic characterization and the Rouse time. From the ERS model, a parameter-free universal relation of monomeric friction reduction as a function of segmental stretch can be derived. PCN simulations using this friction reduction relation are shown to reproduce quantitatively the experimental data even without any fitting parameter. The comparison with results of the earlier PCN simulation results with friction depending on segmental orientation demonstrates that the two friction relations examined work equally well which implies that the physical mechanisms of friction reduction are still open for discussion.

DOI： 10.1007/s00397-022-01373-w

世界情勢とInternational Committee on Rheology 国際誌

増渕雄一

日本レオロジー学会誌 50 巻 ( 5 ) 頁： 391 - 392 2022年12月

CNT Gels Formed by a Triptycene Analogue Enabling Coexistence of CNT-gelator and Intergelator Interactions 査読有り国際誌

Ushiroguchi R., Suizu R., Matsunaga Y., Omachi H., Doi Y., Masubuchi Y., Bandow S., Awaga K.

Chemistry Letters 51 巻 ( 11 ) 頁： 1070 - 1073 2022年11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：Chemistry Letters

We report carbon nanotube (CNT) gels, formed by mechanically mixing CNTs, organic solvents, and a small molecule, Trip-Phz, that have a strong affinity for fullerene materials. There is a clear threshold value in the amount of Trip-Phz needed for the transition from soft to hard gels.

DOI： 10.1246/cl.220319

Viscoelastic properties of comb-shaped ring polystyrenes 招待有り査読有り国際誌 Open Access

Doi Y., Kitamura J., Uneyama T., Masubuchi Y., Takano A., Takahashi Y., Matsushita Y.

Polymer Journal 54 巻 ( 11 ) 頁： 1267 - 1277 2022年11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

In this study, we examined the viscoelastic properties of a series of comb-shaped ring (RC) polystyrene samples with different branch chain lengths, i.e., the molecular weights of the ring backbone Mbb (≃ 4Me where Me is the entanglement molecular weight) and branch chains Mbr (≃ Me, 2Me, and 4Me). Even for the RC sample with the shortest branch chains, a plateau region was observed for the dynamic modulus G*(ω) in the middle angular frequency ω region, suggesting that intermolecular branch chain entanglement occurred. In the ω region between the plateau and terminal regions, G*(ω) was observed with a weaker ω dependence than the terminal relaxation. This behavior was more pronounced for RC samples with shorter branch chains and for the corresponding linear comb (LC) samples than for the RC ones. The molecular weight dependence of the zero-shear viscosity η0 and the steady-state recoverable compliance Jeo of the RC and LC samples was evaluated, and the effects of different backbone molecular structures (i.e., ring or linear) on the terminal relaxation behavior was discussed. Moreover, the G*(ω) data were analyzed with two models: the comb-Rouse model, in which the structures of the RC/LC molecules are taken into account by graph theory, and the Milner-McLeish model for entangled star-shaped polymers. The former model qualitatively described the terminal relaxation behavior of G*(ω) at low ω but failed to reproduce the plateau in the middle ω range. Conversely, the latter model described the entanglement plateau in the middle ω range, but the difference in the terminal relaxation regime for the RC/LC samples seen in the data and the comb-Rouse model disappeared.

DOI： 10.1038/s41428-022-00686-0

Stress Tensor of Single Rigid Dumbbell by Virtual Work Method 査読有り国際誌 Open Access

Uneyama Takashi, Oishi Tatsuma, Ishida Takato, Doi Yuya, Masubuchi Yuichi

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

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：The Society of Rheology, Japan

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