研究者詳細 - 増渕　雄一

論文 - 増渕　雄一

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Coarse-grained molecular dynamics simulations for oxidative aging of polymers under various O<sub>2 </sub>concentrations 査読有り国際誌 Open Access

Ishida, T; Haremaki, K; Koide, Y; Uneyama, T; Masubuchi, Y

POLYMER DEGRADATION AND STABILITY 239 巻 2025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：Polymer Degradation and Stability

Modeling of polymer oxidative aging has been actively studied since the 1990s. Insights from these studies suggest that the transport of oxygen and radicals significantly influences aging heterogeneity, alongside chemical reaction kinetics. A recent simulation study [Ishida et al., Macromolecules, 56(21), 8474-8483, 2023] demonstrated that mesoscale heterogeneity arises when the H-abstraction reaction occurs faster than the relaxation times of polymer chains. In this study, the simulations were extended by modeling the rate of oxygen addition to polymer radicals (k<inf>2</inf>) to reflect the effects of the O₂ concentration. In this work, polypropylene was chosen as a representative example of the target polymer. Three key aspects of oxidative aging behavior were found to be influenced by the O<inf>2</inf> addition rate: (i) reaction kinetics, (ii) the degree of heterogeneity, and (iii) amount of crosslinking. Namely, reducing O<inf>2</inf> concentration slows the conversion of polymer radicals into H-abstractable peroxyl radicals. This deceleration delays H-abstraction reactions, increases the number of polymer radicals, and promotes crosslinking reactions between two polymer radicals.

DOI： 10.1016/j.polymdegradstab.2025.111404

Primitive chain network simulations of double peaks in viscosity growth curves of densely branched pom-pom polymer melts in fast shear flows 査読有り国際共著国際誌

Masubuchi, Y; Schussmann, MG; Hyun, K; Wilhelm, M; Hirschberg, V; Ianniruberto, G; Marrucci, G

RHEOLOGICA ACTA 64 巻 ( 6-7 ) 頁： 263 - 271 2025年7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：Rheologica Acta

Despite many attempts, the molecular mechanism of the nonlinear viscoelastic response of polymeric liquids in fast shear flows has not yet been fully elucidated. In this study, we examined the viscosity growth curves for a few well-characterized, nearly monodisperse, densely branched pom-pom polystyrene melts. The viscosity growth curves exhibit double peaks rather than the widely reported (for most polymer melts) single peak. To investigate the underlying molecular mechanism responsible for the observed behavior, we conducted primitive chain network (multi-chain sliplink) simulations, and found that the first and second peaks correspond to arm orientation and backbone stretch, respectively. We further observed that backbone stretch is reduced by coherent molecular tumbling at the flow start-up, and hence the second peak intensity comes out comparable to that of the orientation-induced first peak. In our sample, the number of backbone entanglements is small, so the mechanism of branchpoint withdrawal does not play a significant role.

DOI： 10.1007/s00397-025-01502-1

Persistence Length and Plateau Modulus of Semiflexible Entangled Polymers in Primitive Chain Network Simulations 査読有り国際誌 Open Access

Masubuchi Y., Tassieri M., Ianniruberto G., Marrucci G.

Nihon Reoroji Gakkaishi 53 巻 ( 3 ) 頁： 119 - 125 2025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：Nihon Reoroji Gakkaishi

The relationship between the plateau modulus (G<inf>0</inf>) and the persistence length (L<inf>p</inf>) of entangled semiflexible polymers is still uncertain. Some previous theoretical models have predicted that G<inf>0</inf> decreases with increasing L<inf>p</inf>, while experiments indicated the opposite. In this study, we extend the primitive chain network (PCN) model to incorporate bending rigidity at the scale of the entanglement length, consistently with the coarse graining of the model. Simulations investigate the effects of rigidity (and of molecular weight) on chain conformation and relaxation modulus. Our results reveal a relationship described as G<inf>0</inf> ~ L<inf>p</inf><sup>2/3</sup>, indicating that G<inf>0</inf> increases with increasing L<inf>p</inf>, consistently with experiments. It should be considered, however, that implicit in our simulations is the condition that the entanglement length is kept fixed with changing L<inf>p</inf>

DOI： 10.1678/rheology.53.119

Phantom Chain Simulations for the Fracture of Star Polymer Networks on the Effect of Arm Molecular Weight 査読有り国際誌

Masubuchi, Y

MACROMOLECULES 58 巻 ( 12 ) 頁： 6399 - 6405 2025年6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：Macromolecules

This study investigated the fracture of star polymer networks made from pre-polymers with various arm molecular weights in the range, 2 ≤ N<inf>a</inf> ≤ 20, for node functionalities 3 ≤ f ≤ 8 and conversion ratios 0.6 ≤ φ<inf>c</inf> ≤ 0.95 by phantom chain simulations. The networks were created via end-linking reactions of star polymers dispersed in a simulation box with a fixed monomer density ρ = 8. The resultant networks were alternatively subjected to energy minimization and uniaxial stretch until the break. The stretch at the break, λ<inf>b</inf>, depended on the strand molecular weight N<inf>s</inf> = 2N<inf>a</inf> + 1 with a power-law manner described as λ<inf>b</inf> ∼ N<inf>s</inf><sup>0.67</sup>, consistent with the experiment. However, the strand length before stretch is proportional to N<inf>s</inf><sup>0.5</sup>, which does not explain the observed N<inf>s</inf>-dependence of λ<inf>b</inf>. The analysis based on the non-affine deformation theory does not interpret the phenomenon either. Instead, the increase of normalized pre-polymer concentration concerning the overlapping concentration with increasing N<inf>s</inf> explains the result through a rise in the fraction of broken strands.

DOI： 10.1021/acs.macromol.5c00475

Nonmonotonic concentration dependence of the self-diffusion coefficient of surfactants in wormlike micellar solutions 査読有り国際誌 Open Access

Koide, Y; Ishida, T; Uneyama, T; Masubuchi, Y

JOURNAL OF CHEMICAL PHYSICS 162 巻 ( 17 ) 2025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：Journal of Chemical Physics

We investigate the concentration dependence of surfactant diffusion in wormlike micellar solutions using dissipative particle dynamics simulations. The simulations show that the self-diffusion coefficient of surfactants exhibits a nonmonotonic dependence on the surfactant concentration, as observed in previous experiments. We quantitatively reveal that this nonmonotonic behavior results from the competition between micellar center-of-mass diffusion and surfactant diffusion within micelles by decomposing the mean-square displacement of surfactants into the corresponding contributions. Furthermore, our detailed analyses demonstrate how the competition between the two diffusion mechanisms is governed by the aggregation number distribution, the dynamics of individual surfactants and micelles, and the kinetics of micellar scission and recombination.

DOI： 10.1063/5.0266470

Prediction of induced fluxes in reverse nonequilibrium molecular dynamics 査読有り国際誌

Oishi, T; Koide, Y; Ishida, T; Masubuchi, Y; Uneyama, T

JOURNAL OF CHEMICAL PHYSICS 162 巻 ( 5 ) 2025年2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 Chemical Physics

Reverse nonequilibrium molecular dynamics (RNEMD) simulations impose a flux by swapping the velocities of two particles. This method allows for the calculation of transport coefficients, such as thermal conductivity and viscosity. The relation between the induced fluxes and the control parameters of RNEMD (such as the time interval between successive swap events) is not clear. Thus, trial-and-error is required to realize the desired fluxes in RNEMD simulations. In this study, we develop a theoretical framework using extreme value statistics to estimate the relation between the time interval and the resulting induced fluxes. Our RNEMD simulations, conducted with varying time intervals, confirm that the theoretical predictions are quantitatively consistent with the simulation results when the time interval exceeds the momentum relaxation time. Our RNEMD simulations also show that our theoretical predictions, which are valid for a large number of particles for swap candidates, work well even for a relatively small number of particles for swap candidates. These findings demonstrate that the induced fluxes can be reliably estimated, providing a valuable tool for selecting appropriate RNEMD parameters for simulations.

DOI： 10.1063/5.0236799

Brownian simulations for fracture of star polymer phantom networks 招待有り査読有り国際誌

Masubuchi, Y; Koide, Y; Ishida, T; Uneyama, T

POLYMER JOURNAL 2024年11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：Polymer Journal

According to a recent simulation study [Masubuchi et al., Macromolecules, 56, 9359 (2023)], the cycle rank plays a significant role in determining the fracture characteristics of network polymers. However, the previous studies considered only energy-minimized networks without including the effects of thermal agitation. To address this gap, this study conducted Brownian dynamics simulations at various stretch rates. The results showed that even with Brownian motion, the strain and stress at break obtained for different node functionalities and conversion ratios exhibited master curves when plotted versus the cycle rank. These master curves depend on the strain rate, indicating that the strain and stress at break decrease with decreasing strain rate. The curves are qualitatively similar to those observed in energy-minimized simulations, even though the competition among Brownian motion, elongation, and bond scission affects the fracture process.

DOI： 10.1038/s41428-024-00992-9

Reverse Nonequilibrium Molecular Dynamics Simulations of a Melt of Kremer-Grest Type Model under Fast Shear 査読有り国際共著国際誌

Oishi, T; Koide, Y; Ishida, T; Uneyama, T; Masubuchi, Y; Müller-Plathe, F

JOURNAL OF CHEMICAL THEORY AND COMPUTATION 20 巻 ( 21 ) 頁： 9666 - 9672 2024年10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：Journal of Chemical Theory and Computation

Although the reverse nonequilibrium molecular dynamics (RNEMD) simulation method has been widely employed, the range of applicability is yet to be discussed. In this study, for the first time, we systematically examine the method against an unentangled melt of the Kremer-Grest type chain. The simulation results indicate that as the shear rate increases, the temperature and density become inhomogeneous. However, the average viscosity remains consistent with the results obtained using the SLLOD method under homogeneous temperature and density. We also confirm that the temperature-density inhomogeneity does not significantly affect polymer conformation.

DOI： 10.1021/acs.jctc.4c01007

Phantom chain simulations for the fracture of star polymer networks with various strand densities 招待有り査読有り国際誌

Masubuchi, Y; Ishida, T; Koide, Y; Uneyama, T

SOFT MATTER 20 巻 ( 36 ) 頁： 7103 - 7110 2024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：Soft Matter

Despite many attempts, the relationship between the fracture and structure of polymer networks is yet to be clarified. For this problem, a recent study on phantom chain simulations [Y. Masubuchi et al., Macromolecules, 2023, 56, 9359-9367.] has demonstrated that the fracture characteristics obtained for polymer networks with various node functionalities and conversion ratios lie on master curves if they are plotted against cycle rank, which is the number of closed loops in the network per network node. In this study, we extended the simulation to the effect of prepolymer concentration c on the relationships between the cycle rank and fracture characteristics within the concentration range of 1 ≲ c/c* ≲ 10, concerning the overlapping concentration c*. We created networks from sols of star-branched phantom bead-spring chains via an end-linking reaction between different chains through Brownian dynamics simulations upon varying the number of branching arms f from 1 to 8, and the conversion ratio φc from 0.6 to 0.95. For the resultant networks, the cycle rank ξ was consistent with the mean-field theory. The networks were uniaxially stretched with energy minimization until break to obtain modulus G, strain at break ϵb, stress at break σb, and work for fracture Wb. As reported earlier, ϵb data for various f and φc are located on a master curve if plotted against ξ. The other quantities also draw master curves as functions of ξ if normalized by the branch point density υbr. The master curves depend on c; as c increases, all the mechanical characteristics monotonically increase. If we plot σb/υbr and Wb/υbr against G/υbr, the data for various f and φc lie on master curves but depending on c. Consequently, the fracture characteristics are not solely described by the modulus.

DOI： 10.1039/d4sm00726c

Polyion Hydrogels of Polymeric and Nanofibrous Carboxymethyl Cellulose and Chitosan: Mechanical Characteristics and Potential Use in Environmental Remediation 査読有り国際誌

Kawate T., Wang Y., Chan K., Shibata N., Doi Y., Masubuchi Y., Zinchenko A.

Gels 10 巻 ( 9 ) 2024年9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：Gels

Recently, cellulose and other biomass nanofibers (NFs) have been increasingly utilized in the design of sustainable materials for environmental, biomedical, and other applications. However, the past literature lacks a comparison of the macromolecular and nanofibrous states of biopolymers in various materials, and the advantages and limitations of using nanofibers (NF) instead of conventional polymers are poorly understood. To address this question, hydrogels based on interpolyelectrolyte complexes (IPECs) between carboxymethyl cellulose nanofibers (CMCNFs) and chitosan (CS) were prepared by ele+ctrostatic cross-linking and compared with the hydrogels of carboxymethyl cellulose (CMC) and CS biopolymers. The presence of the rigid CMCNF altered the mechanism of the IPEC assembly and drastically affected the structure of IPEC hydrogels. The swelling ratios of CMCNF-CS hydrogels of ca. 40% were notably lower than the ca. 100–300% swelling of CMC-CS hydrogels. The rheological measurements revealed a higher storage modulus ((Formula presented.)) of the CMCNF-CS hydrogel, reaching 13.3 kPa compared to only 3.5 kPa measured for the CMC-CS hydrogel. Further comparison of the adsorption characteristics of the CMCNF-CS and CMC-CS hydrogels toward Cu2+, Cd2+, and Hg2+ ions showed the slightly higher adsorption capacity of CMC-CS for Cu2+ but similar adsorption capacities for Cd2+ and Hg2+. The adsorption kinetics obeyed the pseudo-second-order adsorption model in both cases. Overall, while the replacement of CMC with CMCNF in hydrogel does not significantly affect the performance of such systems as adsorbents, CMCNF imparts IPEC hydrogel with higher stiffness and a frequency-independent loss ((Formula presented.)) modulus and suppresses the hydrogel swelling, so can be beneficial in practical applications that require stable performance under various dynamic conditions.

DOI： 10.3390/gels10090604

Coarse-grained molecular dynamics simulation of oxidative aging of polymers -effect of free radical diffusivity - 招待有り査読有り国際誌

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

POLYMER JOURNAL 2024年8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

Recently, we developed an oxidative aging simulation technique that explicitly considers the transport of radicals by combining oxidation kinetics with coarse-grained molecular dynamics [1]. The current study explores the role of the free radical diffusivity of oxidative aging in polymers, with a focus on its effects on the heterogeneity of spatiotemporal structures and reaction kinetics, through coarse-grained simulations. By examining two distinct systems, including a heterosystem with a high reaction rate and a quasi-homosystem with a low reaction rate, we investigated how the diffusivity of free radicals influences the oxidative aging process. We examined three different diffusivity levels of radicals. For the slowest case, the radical diffusivity is slightly faster than that of the single polymer segment, whereas for the fastest case, the radical diffuses infinitely faster than the polymers. The aging simulations revealed that the variations in free radical diffusivity quantitatively change the reaction kinetics and spatiotemporal structures without qualitatively altering the overall aging behavior. Specifically, in a heterosystem, lower radical diffusivity slows the oxidation kinetics by increasing fluctuations in the local conversion ratios. In contrast, in a quasi-homosystem, reduced radical diffusivity slightly amplifies the heterogeneity of structures in the early aging stages; however, in a high-conversion region, the aged state becomes homogeneous regardless of the degree of radical diffusivity.

DOI： 10.1038/s41428-024-00942-5

その他リンク： https://www.nature.com/articles/s41428-024-00942-5

Primitive Chain Network Simulations for Double Peaks in Shear Stress under Fast Flows of Bidisperse Entangled Polymers 招待有り査読有り国際誌

Masubuchi Y.

Polymers 16 巻 ( 11 ) 頁： 1455-1 - 1455-10 2024年5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：Polymers

A few experiments have reported that the time development of shear stress under fast-startup shear deformations exhibits double peaks before reaching a steady state for bimodal blends of entangled linear polymers under specific conditions. To understand this phenomenon, multi-chain slip-link simulations, based on the primitive chain network model, were conducted on the literature data of a bimodal polystyrene solution. Owing to reasonable agreement between their data and our simulation results, the stress was decomposed into contributions from long- and short-chain components and decoupled into segment number, stretch, and orientation. The analysis revealed that the first and second peaks correspond to the short-chain orientation and the long-chain stretch, respectively. The results also implied that the peak positions are not affected by the mixing of short and long chains, although the intensity of the second peak depends on mixing conditions in a complicated manner.

DOI： 10.3390/polym16111455

Dissipative Particle Dynamics Simulation Plus Slip-Springs for Entangled Polymers with Various Slip-Spring Densities 査読有り国際共著国際誌

Masubuchi, Y; Guo, HX; Wang, F; Khomami, B; Boudaghi-Khajehnobar, M; Doi, Y; Ishida, T; Uneyama, T

MACROMOLECULES 57 巻 ( 10 ) 頁： 4867 - 4877 2024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：Macromolecules

Slip-spring models are valuable tools for simulating entangled polymers, bridging the gap between bead-spring models with excluded volume and network models with presumed reptation motion. This study focuses on the DPD-SS (Dissipative Particle Dynamics-Slip-Spring) model, which introduces slip springs into the standard DPD polymer model with soft-core interactions. By systematically adjusting the activity of slip springs, the density of slip springs within the system is varied. Simulation results demonstrate the compatibility of models with different slip-spring densities in terms of diffusion and linear relaxation modulus when the average number of slip springs per chain is the same. The conversion between DPD-SS models concerning length and time is achieved through Rouse scaling, which utilizes the average number of DPD beads between consecutive anchoring points of slip springs. Additionally, the modulus conversion is accomplished through the plateau modulus that takes account of fluctuations around entanglement. Notably, diffusion and relaxation modulus from the DPD-SS model align with those reported for standard Kremer-Grest and DPD models featuring strong repulsive interactions.

DOI： 10.1021/acs.macromol.4c00280

Effect of Surface Treatment for Iron Particles with Excessive Amounts of Silane Coupling Agent on Rheological Properties of Magnetorheological Fluids 招待有り査読有り国際誌

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

Nihon Reoroji Gakkaishi 52 巻 ( 2 ) 頁： 99 - 105 2024年4月

担当区分：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：Nihon Reoroji Gakkaishi

We investigated the effect of surface treatment for iron particles in the magnetorheological fluids (MRFs) on rheological properties. Silane coupling treatment with an excess amount of dodecyltrimethoxysilane (DTMS) was conducted for iron particles. MRFs were prepared by dispersing iron particles with and without the silane coupling treatment. MRFs with iron particles washed with n-hexane after the silane coupling treatment was also prepared. The rheological properties of MRFs were measured in the presence and absence of a magnetic field. Without a magnetic field, MRFs with the silanecoupled particles exhibited higher stress than the untreated particles. Under a magnetic field, MRFs with the silane-coupled particles showed lower stress than the untreated analogue. These results imply that the silane coupling treatment enhances the aggregation of particles without a magnetic field but suppresses the cluster formation under the magnetic field. MRFs with the washed iron particles exhibited almost the same rheological properties as that with the untreated particles. Thus we suggest that DTMS is mainly physically absorbed on the surface of iron particles, without forming chemical bonds.

DOI： 10.1678/rheology.52.99

Anisotropy of Shear Relaxation in Primitive Chain Network Simulations for Entangled Polymers Confined between Flat Walls 招待有り査読有り国際誌

Masubuchi Y.

Nihon Reoroji Gakkaishi 52 巻 ( 2 ) 頁： 77 - 82 2024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：Nihon Reoroji Gakkaishi

Anisotropic shear relaxation is an interesting but rarely discussed issue in polymer dynamics under confinement. According to the earlier study of bead spring simulations for an unentangled polymer melt confined between two flat plates, the shear relaxation modulus taken perpendicular to the interface is accelerated by decreasing the distance between plates, whereas the parallel component is unchanged [Abberton et al., Macromolecules, 48, 7631, 2015]. This study observed similar anisotropic shear relaxation for entangled polymer melts under confinement in multi-chain slip-link simulations (primitive chain network simulations) for shear relaxation moduli obtained by the Green-Kubo formula. The analysis demonstrated that the accelerated relaxation in the perpendicular component reflects the Rouse-type constraint release dynamics, for which the coarsening is upper-limited by the geometry. This result suggests a novel mechanism for anisotropic shear relaxation different from the modified chain statistics under confinement considered for unentangled systems unless the obtained relaxation moduli reflect artifacts from the use of the Green-Kubo formula under confinement.

DOI： 10.1678/RHEOLOGY.52.77

Phantom Chain Simulations for Fracture of End-linking Networks 査読有り国際誌

Yuichi Masubuchi

Polymer 297 巻頁： 126880-1 - 126880-8 2024年3月

Phantom chain simulations for the effect of stoichiometry on the fracture of star-polymer networks 査読有り国際誌

Yuichi Masubuchi

Nihon Reoroji Gakkaishi 52 巻 ( 1 ) 頁： 21 - 26 2024年2月

Phantom chain simulations for fracture of polymer networks created from star polymer mixtures of different functionalities 査読有り国際誌

Masubuchi Y.

Polymer Journal 56 巻頁： 163 - 171 2023年12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：Polymer Journal

Fujiyabu et al. [1] experimentally reported that mixing of 3-arm star prepolymers into 4-arm analogs improves the toughness of the resultant polymer networks compared to that of the base network composed of only 4-arm star polymers. The present study investigated the mechanism of this phenomenon based on phantom chain simulations for polymer networks consisting of mixtures of star branch prepolymers with equal arm length and different arm numbers, (f1,f2)=(3, 4) , (3, 6) and (3, 8) , for various f1= 3 prepolymer fractions φ3 . These networks were created via end-linking reactions between prepolymers traced by a Brownian dynamics scheme, and the network structure was stored at different conversion ratios φc , ranging from 0.6 to 0.9. The cycle rank of the gelated networks ξ is entirely consistent with that given by mean-field theory, demonstrating that the examined network structure is statistically valid. The networks were stretched with energy minimization until the break, and fracture characteristics including strain at break εb , stress at break σb , work for fracture Wb , and the ratio of broken strands φbb , were obtained. Plots of εb , σb/ φbb , and Wb/ φbb versus ξ roughly follow the master curves reported for the base networks without mixing, implying that the change of fracture properties by the mixing of f1= 3 mainly corresponds to a decrease in ξ . The mixing slightly suppresses σb/ φbb and Wb/ φbb for large f2 cases compared to the base networks because of a biased breakage at the network strands without extenders, which are prepolymers with only two reacted arms. The analysis also revealed a new master curve for the ξ -dependence of the molecular weight of broken strands.

DOI： 10.1038/s41428-023-00862-w

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

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

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

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