研究者詳細 - 増渕　雄一

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

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

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

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

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

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

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

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

Primitive Chain Network Simulations for Shear Rheology of Poly(propylene carbonate) Melts 査読有り国際誌

Masubuchi Yuichi, Yang Lixin, Uneyama Takashi, Doi Yuya

Nihon Reoroji Gakkaishi 50 巻 ( 4 ) 頁： 305 - 312 2022年9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：The Society of Rheology, Japan

Although chemistry dependence in the non-linear rheology of polymers has been rather established for uniaxial elongations, it has not been frequently discussed for fast shear. In this study, to see the effect of orientation-dependent monomeric friction on the shear rheology, we conducted primitive chain network simulations for a few poly(propylene carbonate) melts, for which we have determined the friction model from the uniaxial data recently [Yang et al., Nihon Reoroji Gakkaishi, 50, 127–135 (2022)]. The simulation qualitatively reproduced typical non-linear behaviors, such as shear thinning and stress overshoot, under fast shears. The agreement with experimental data became better when the friction was varied according to the segment orientation. In particular, the shear rate dependence of the peak position for the stress overshoot (i.e., the peak stress and the strain at the peak) was better reproduced. This result implies that chemistry-dependent friction may probably be discussed from the stress overshoot under high shear.

DOI： 10.1678/rheology.50.305

Brownian simulations for tetra-gel-type phantom networks composed of prepolymers with bidisperse arm length 招待有り査読有り国際誌

Masubuchi Yuichi, Yamazaki Ryohei, Doi Yuya, Uneyama Takashi, Sakumichi Naoyuki, Sakai Takamasa

SOFT MATTER 18 巻 ( 25 ) 頁： 4715 - 4724 2022年6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：Soft Matter

We studied the effect of arm length contrast of prepolymers on the mechanical properties of tetra-branched networks via Brownian dynamics simulations. We employed a bead-spring model without the excluded volume interactions, and we did not consider the solvent explicitly. Each examined 4-arm star branch prepolymer has uneven arm lengths to attain two-against-two (2a2) or one-against-three (1a3) configurations. The arm length contrast was varied from 38-2 to 20-20 for 2a2, and from 5-25 to 65-5 for 1a3, with the fixed total bead number of 81, including the single bead located at the branch point for prepolymers. We distributed 400 molecules in the simulation box with periodic boundary conditions, and the bead number density was fixed at 4. We created polymer networks by cross-end-coupling of equilibrated tetra-branched prepolymers. To mimic the experiments of tetra gels, we discriminated the molecules into two types and allowed the reaction only between different types of molecules at their end beads. The final conversion ratio was more than 99%, at which unreacted dangling ends are negligible. We found that the fraction of double linkage, in which two of the four arms connect a pair of branch points, increases from 3% to 15% by increasing the arm length contrast. We stretched the resultant tetra-type networks to obtain the ratio of mechanically effective strands. We found that the ratio is 96% for the monodisperse system, decreasing to 90% for high arm length contrast. We introduced bond scission according to the bond stretching to observe the network fracture under sufficiently slow elongation. The fracture behavior was not correlated with the fraction of double linkage because the scission occurs at single linkages.

DOI： 10.1039/d2sm00488g

Effects of Slip-Spring Parameters and Rouse Bead Density on Polymer Dynamics in Multichain Slip-Spring Simulations 招待有り査読有り国際誌

Masubuchi Yuichi, Doi Yuya, Uneyama Takashi

JOURNAL OF PHYSICAL CHEMISTRY B 126 巻 ( 15 ) 頁： 2930 - 2941 2022年4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 Physical Chemistry B

The multichain slip-spring (MCSS) model is one of the coarse-grained models of polymers developed in the niche between bead-spring models and tube type descriptions. In this model, polymers are represented by Rouse chains connected by virtual springs that temporally connect the chains, hop along the chain, and are constructed and annihilated at the chain ends. Earlier studies have shown that MCSS simulations can nicely reproduce entangled and unentangled polymer dynamics. However, the model parameters have been chosen arbitrarily, and their effects have not been reported. In this study, for the first time, we systematically investigated the effects of model parameters: fugacity of virtual springs, its intensity, and the Rouse bead density. We validated the employed simulation code by confirming that the statistics of the system follow the theoretical setup. Namely, the virtual spring density is correctly controlled, and polymer chains exhibit ideal chain statistics irrespective of the chosen parameter values. For diffusion and linear viscoelasticity, simulation results obtained for different parameters can be superposed with each other by conversion factors for the bead number per chain and units of length, time, and modulus. These conversion factors follow scaling laws concerning the number of Rouse segments between two consecutive anchoring points of virtual springs along the polymer chain. Besides, diffusion and viscoelasticity excellently agree with literature data for the standard bead-spring simulation. These results imply that the coarse-graining level for the MCSS model can be arbitrarily chosen and controlled by model parameters.

DOI： 10.1021/acs.jpcb.2c00697

Analysis of Elongational Viscosity of Entangled Poly (Propylene Carbonate) Melts by Primitive Chain Network Simulations 招待有り査読有り国際誌

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

Polymers 14 巻 ( 4 ) 頁： 741-1 - 741-15 2022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：Polymers

It has been established that the elongational rheology of polymers depends on their chemistry. However, the analysis of experimental data has been reported for only a few polymers. In this study, we analyzed the elongational viscosity of poly (propylene carbonate) (PPC) melts in terms of monomeric friction via primitive chain network simulations. By incorporating a small polydispersity of materials, the linear viscoelastic response was semi-quantitatively reproduced. Owing to this agreement, we determined units of time and modulus to carry out elongational simulations. The simulation with constant monomeric friction overestimated elongational viscosity, whereas it nicely captured the experimental data if friction decreased with increasing segment orientation. To see the effect of chemistry, we also conducted the simulation for a polystyrene (PS) melt, which has a similar entanglement number per chain and a polydispersity index. The results imply that PPC and PS behave similarly in terms of the reduction of friction under fast deformations.

DOI： 10.3390/polym14040741

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

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

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

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

Nonlinear shear and elongational rheology of entangled poly(propylene carbonate) (PPC) melts having different molecular weights with relatively narrow molecular weight distribution are examined. In shear measurements, the PPCs exhibit a typical shear thinning behavior with stress overshoot at high shear rates. In the shear rate dependence of the steadystate viscosity, the PPCs do not violate the empirical Cox-Merz rule, which is known to be valid for many other entangled polymer melts. In uniaxial elongational measurements, the viscosity growth functions of the PPCs show a weak deviation from the linear viscoelastic (LVE) envelope to the higher side at the high Weissenberg number Wid (= ͘ετd, where ͘ε is the elongation rate and τd is the characteristic disengagement time). The steady-state viscosity of the PPCs shows an elongational thinning as a function of ͘ε −0.5 within an error. These results are similar to some other polymer melts such as polystyrene (PS). In addition, the normalized elongational viscosity growth functions of PPC and PS with a similar entanglement number Z, are compared. The PPC exhibits a similar viscosity growth curve to the PS at the same Wid. This result suggests that the degree of the monomeric friction reduction originated from the stretch/orientation of PPC under fast elongational flow might occur at the same level as PS.

DOI： 10.1678/rheology.50.127

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

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

Rheologica Acta 60 巻 ( 9 ) 頁： 511 - 519 2021年7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：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

その他リンク： https://link.springer.com/article/10.1007/s00397-021-01286-0/fulltext.html

Wall slip in primitive chain network simulations of shear startup of entangled polymers and its effect on the shear stress undershoot 査読有り国際共著国際誌

Yuichi Masubuchi, Dimitris Vlassopoulos, Giovanni Ianniruberto, Giuseppe Marrucci

Journal of Rheology 65 巻 ( 2 ) 頁： 213 - 223 2021年3月

Quantitative bridging between full-atomistic and bead-spring models for polybutadiene and poly(butadiene-styrene) copolymers 査読有り国際誌

Akinori Baba, Yuichi Masubuchi

Journal of Chemical Physics 154 巻 ( 4 ) 頁： 044901-1 - 044901-14 2021年1月

DNA-Chitosan Hydrogels: Formation, Properties, and Functionalization with Catalytic Nanoparticles 査読有り国際共著国際誌

Kohki Morikawa, Yuichi Masubuchi, Yury Shchipunov, Anatoly Zinchenko

ACS Applied Bio Materials 4 巻頁： 1823 - 1832 2021年

Plateau Moduli of Several Single-Chain Slip-Link and Slip-Spring Models 査読有り国際誌

Takashi Uneyama, Yuichi Masubuchi

Macromolecules 54 巻 ( 3 ) 頁： 1338 - 1353 2021年

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

Masubuchi Yuichi, Kida Takumitsu, Doi Yuya, Uneyama Takashi

NIHON REOROJI GAKKAISHI 49 巻 ( 5 ) 頁： 337 - 345 2021年

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

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