arXiv subjects

Yuichi Masubuchi

Publications and source records attributed to Yuichi Masubuchi.

At least 19 recordsLinked to original sources

arXiv2026

A unified description of flow-induced scission of wormlike micelles under shear and extensional flows

We investigate flow-induced scission of wormlike micelles under different flow kinematics using dissipative particle dynamics simulations of surfactant solutions in shear, uniaxial extensional, planar extensional, and biaxial extensional flows. The average lifetime of wormlike micelles is used to quantify the degree of scission. While flow-induced scission occurs in all flow types when the deformation rate is sufficiently high, the dependence of the average lifetime on the deformation rate differs among flow types. To provide a unified description, we introduce an effective extension rate determined by the velocity gradient tensor and micellar orientation. When expressed in terms of this effective extension rate, the average lifetimes obtained under all flow types considered collapse onto a single curve. These results demonstrate that a unified description of flow-induced scission requires not only the strength and kinematics of the imposed flow, but also the micellar orientation relative to the extensional direction.

cond-mat.soft↗

arXiv2026

Stress Drops Associated with Surface Crack Formation in Photo-aged Polypropylene during Three-Point Bending

Using three-point bending, this study investigates surface-crack formation in photo-aged polypropylene (PP) that has a depth-dependent aging gradient. PP undergoes embrittlement under ultraviolet (UV) irradiation, and because the photo-oxidation proceeds inward from the irradiated surface, the embrittlement develops non-uniformly across the specimen thickness. PP specimens were mildly photo-aged by UV irradiation and had not yet developed visible surface cracks. Each specimen was bent in two configurations: with the UV-irradiated ("aged") surface on the tensile side, and with the opposite ("reverse") surface on the tensile side. When the aged surface was on the tensile side, the stress-strain curves exhibited several discrete stress drops, and in-situ side-view observation confirmed that the formation of each new surface crack coincided with a stress drop. In contrast, no clear stress drops were observed when the reverse surface was on the tensile side. These results show that the through-thickness gradient of embrittlement is directly reflected in the bending stress-strain response. Uniaxial tensile testing, the standard method for evaluating mechanical properties, formally assumes a nominally uniform deformation across the cross-section and therefore reflects the spatially averaged response. Three-point bending, by contrast, imposes the largest tensile strain at the specimen surface and thus selectively probes the embrittled surface layer, making it an effective method for detecting the surface embrittlement of photo-aged polymers.

cond-mat.soft↗

arXiv2026

A Generalized Mechanical Model for the Cycle Rank Dependence of Stretch at Break in Phantom Chain Star Polymer Networks

A simple mechanical model was recently proposed to explain the universality of stretch at break ({\lambda}_b) as a function of cycle-rank density ({\xi}) in phantom-chain network simulations [J Non-Newtonian Fluid Mech., 349, 105620 (2026)]. Here, that model is reformulated as a series of the bottleneck strand and the surrounding network, yielding {\lambda}_b-1=({\lambda}_bs-1)[1+{\nu}_h/(1+c{\xi})]. In this formula, {\lambda}_bsis the stretch at break of the bottleneck strand, {\nu}_h is the number of stiff units in series along the rupture path, and c is a geometric constant for the parallel redundancy of the medium. Since c and {\nu}_hare difficult to separate over the examined range of {\xi}, c is fixed, and {\lambda}_bs and {\nu}_hare treated as fitting parameters. The formula is applied to phantom-chain simulations of networks with various conditions. In all cases, it reasonably captures the data, and the two parameters represent network characteristics.

cond-mat.soft↗

arXiv2026

Statistics of rupture in phantom chain network simulations

Phantom chain simulations have shown that the mean rupture properties of star polymer networks collapse onto master curves against the cycle rank density $\xi$. This study revisits this universality with a much larger ensemble than in earlier studies to discuss the statistics. Phantom Gaussian networks were made by end-linking star prepolymers, and 1,000 realizations were collected for each of 30 conditions with functionality $f=3$--$8$ and conversion $p=0.60$--$0.95$, giving 30,000 networks in total. For each realization, the breaking stretch $\lambda_b$, the breaking stress $\sigma_b$, the breaking energy $W_b$, and the cycle rank $\xi$ were recorded. The master curves are unchanged by the larger sample, demonstrating that the earlier conclusions reported for the averages of smaller ensembles hold. However, the individual realizations are inherently random, and their statistical properties, rather than the individual values, are examined. At fixed $f,p$, the fluctuation of $\xi$ is small, varying by less than 0.01, whereas $\lambda_b$, $\sigma_b$, and $W_b$ scatter by 0.05--0.3. The fluctuation of $\xi$ is almost uncorrelated with that of the breaking properties. In addition, the scatter has a definite structure; its magnitude decreases with the mean cycle rank density $\xi$, the $\lambda_b$--$\sigma_b$ correlation grows with $\xi$, and the distributions deviate from Gaussian. The $\lambda_b$ distribution is skewed to the right at small $\xi$, whereas $\sigma_b$ is skewed to the left at large $\xi$. These rupture statistics were discussed in the framework of extreme-value statistics to demonstrate that the observed trends are opposite to those of the random fuse model, in which strength decreases with size and weakest-link statistics appear for weak disorder. The difference may reflect the source of fluctuation, i.e., the cross-linking in the present networks.

cond-mat.soft↗

arXiv2026

Slip-link simulations of long-fiber networks under uniaxial compression

A coarse-grained molecular simulation approach originally developed for entangled polymeric liquids is extended to model the mechanical behavior of long-fiber networks. The model, based on the slip-link picture of chain entanglements, resolves the force balance at contact points and accounts for fiber slippage under these topological constraints. Two key governing equations describe the time evolution of contact-point positions and the local fiber fraction between adjacent contact points. A yield-force criterion determines whether contact points are displaced or remain pinned, as well as whether fiber slippage occurs at contact points. Uniaxial compression simulations corresponding to press molding of fiber-reinforced thermoplastics were performed for networks with varying fiber lengths and compression rates. The results were qualitatively consistent with experimental observations of long-fiber thermoplastics. The model captures physics inaccessible to the classical van Wyk theory of fiber network compression, which is quasi-static and insensitive to fiber length. This work demonstrates that the slip-link framework, already validated for polymer melts, provides a promising mesoscale simulation tool for understanding and predicting the processing behavior of non-thermal fiber networks.

cond-mat.soft↗

arXiv2026

Developments in Multi-Chain Coarse-Grained Models for Entangled Polymer Dynamics

This review describes the development and applications of multi-chain coarse-grained simulations for entangled polymer dynamics. The mean-field tube model has long served as the standard paradigm for describing the many-body entanglement problem as the motion of a single chain in a static field; it faces intrinsic limitations when addressing spatial correlations, fluctuations, and complex topological rearrangements. To overcome these limitations, "multi-chain" approaches -- specifically the primitive chain network and multi-chain slip-spring models -- were developed. These simulations explicitly resolve the force balance and topological coupling between multiple chains in three-dimensional space. This review covers the primitive chain network model, which emphasizes real-space force balance, and the multi-chain slip-spring model, which is derived from a well-defined free-energy functional. Linear and nonlinear rheology predictions are discussed, along with molecular mechanisms such as constraint release and stretch/orientation-induced reductions in friction. Extensions to branched polymers, wall-slip phenomena, and network polymers are also mentioned.

cond-mat.soft↗

arXiv2026

Effect of flow kinematics on extensional viscosity of dilute polymer solutions

We investigate the effect of flow kinematics on the extensional viscosity of dilute polymer solutions by conducting dissipative particle dynamics simulations under uniaxial, planar, and biaxial extensional flows. At high extension rates, dilute polymer solutions exhibit strain hardening under these flows, while the quantitative behavior depends on the flow type. To elucidate the physical origin of this flow-kinematics dependence, we relate the extensional viscosity to polymer conformation using an analytical expression derived from a single-chain model. The resulting relation allows us to separate the contribution of flow-induced polymer conformational changes and the purely kinematic contribution determined by the structure of the velocity gradient tensor. When polymers remain almost unperturbed by extensional flows, differences in the extensional viscosity are governed primarily by the purely kinematic effects. In contrast, as polymers are stretched, the gyration radius in the extensional direction becomes the dominant factor, and differences in the stretching degree in this direction lead to corresponding variations in the extensional viscosity.

cond-mat.soft↗

arXiv2026

Universal Scaling of Macroscopic Softening and Microscopic Scission in Phantom Chain Networks

This study demonstrates that the apparent complexity of fracture in phantom-chain polymer networks is fully decoupled into two universal master curves: (i) macroscopic softening governed by the absolute stretch, and (ii) microscopic scission governed solely by the relative stretch. Using the previously proposed network mechanics model, an analytical expression has been derived to quantitatively capture the nonlinear growth of microscopic damage. Combining the softening exponent with polymer-solution scaling yields a simple novel relationship, $\sigma_{nb} / G \propto (c / c^* )^{(-1/3)}$, where $\sigma_{nb}$ is the nominal broken strength, $G$ is the initial shear modulus, $c$ is the prepolymer concentration, and $c^*$ is its overlapping threshold.

cond-mat.soft↗

arXiv2026

A Toy Model for the Cycle Rank Dependence of Stretch at Break in Phantom Chain Network Simulations

The relationship between the topological architecture of polymer networks and their macroscopic rupture remains a fundamental challenge in polymer physics. Recent coarse-grained simulations have revealed that the dependence of stretch at break (\lambda_b) on node functionality and reaction conversion can be unified into a universal master curve when plotted against the cycle rank density (\xi). However, a theoretical derivation explaining this universality has been lacking. This study proposes a simple mechanical model to describe the \xi-dependence of \lambda_b. The polymer network is modeled as a mechanical system consisting of a sequence of springs representing localized, highly stretched strands and the surrounding unstretched network. By relating the stiffness contrast between these regions to the network connectivity defined by \xi, an analytical expression for the stretch at break is derived: \lambda_b-1\propto\sfrac{\left(3\xi+6\right)}{\left(3\xi+2\right)}\ . The proposed model is validated against phantom chain simulations using both Gaussian and finite extensibility (FENE) springs. The theoretical prediction shows reasonable agreement with simulation data, providing a physical basis for the phenomenological universality observed in polymer network rupture.

cond-mat.soft↗

arXiv2025

Relation between extensional viscosity and polymer conformation in dilute polymer solutions

We investigate extensional viscosity and polymer conformation in dilute polymer solutions under uniaxial extensional flow using dissipative particle dynamics simulations. At high extension rates, polymers are significantly stretched by extensional flows, and the extensional viscosity growth function exhibits strain hardening. To reveal their quantitative relation, we adopt an analysis method based on the Rouse-type model. We demonstrate that the extensional viscosity growth function is determined by the instantaneous gyration radii in the parallel and perpendicular directions to the extensional direction and their time derivatives. Our approach also provides a unified description of the steady-state extensional viscosity of dilute polymer solutions for various chain lengths and concentrations in terms of the polymer gyration radius.

cond-mat.soft↗

arXiv2025

A Review on Molecular Simulations for the Rupture of Polymer Networks

Molecular simulations provide a powerful means to unravel the complex relationships between network architecture and the mechanical response of polymer networks, with a particular emphasis on rupture and fracture phenomena. Although simulation studies focused on polymer network rupture remain relatively limited compared to the broader field, recent advances have enabled increasingly nuanced investigations that bridge molecular structures and macroscopic failure behaviors. This review surveys the evolution of molecular simulation approaches for polymer network rupture, from early studies on related materials to state-of-the-art methods. Key challenges, including mismatched spatial and temporal scales with experiments, the validity of coarse-grained models, the choice of simulation protocols and boundary conditions, and the development of meaningful structural descriptors, are critically discussed. Special attention is paid to the assumptions underlying universality, limitations of current methodologies, and the ongoing need for theoretically sound and experimentally accessible network characterization. Continued progress in computational techniques, model development, and integration with experimental insights will be essential for a deeper, predictive understanding of polymer network rupture.

cond-mat.soft↗

arXiv2025

Influence of Stretching Boundary Conditions on Fracture in Phantom Star Polymer Networks: From Volume to Cross-sectional Area Conservation

This study systematically investigates the effect of stretching boundary conditions, ranging from conservation of cross-sectional area to conservation of volume, on the rupture behavior of phantom star polymer networks using energy-minimizing coarse-grained molecular simulations. By continuously varying the deformation parameter, the simulations reveal that true stress and rupture characteristics, such as strain and stress at break and work for rupture, systematically decrease as the boundary condition approaches cross-sectional area conservation. In contrast, nominal stress and the corresponding rupture characteristics exhibit near-independence from boundary conditions, indicating that bond tension remains largely unaffected for phantom networks under the examined conditions. These results clarify that volume expansion primarily drives deviations in true stress and highlight a critical distinction between true and nominal stress-strain definitions. The difference between true and nominal stress-strain relations also affected the scaling exponent for strand length dependence on stretch at break. The findings stress the importance of specifying both deformation boundary conditions and stress-strain definitions in polymer network simulations for accurate interpretation of mechanical properties.

cond-mat.soft↗

arXiv2025

Primitive chain network simulations of the creep of entangled polymers

Although the behavior of entangled polymers in startup shear flows with constant shear rates has been thoroughly investigated, the response under creep has not been frequently considered. In this study, primitive chain network simulations, based on a multi-chain sliplink model, are modified so as to describe creep experiments. Creep simulations are compared to a literature dataset of an entangled polybutadiene solution, and qualitative agreement is found in the nonlinear range, i.e., under large stresses. Simulations allow one to extract details of the transient molecular motion, and results suggest that the deformation-induced disentanglement is relatively mild in the stress-controlled mode as compared to the rate-controlled one, because coherent molecular tumbling at the start of flow is disrupted.

cond-mat.soft↗

arXiv2025

Steady-state extensional viscosity of wormlike micellar solutions via dissipative particle dynamics simulations

We investigate the steady-state extensional viscosity of wormlike micellar solutions using dissipative particle dynamics simulations. As the extension rate increases, the steady-state extensional viscosity initially increases and subsequently decreases after reaching a maximum, as observed in experiments. We reveal that this nonmonotonic behavior arises from the competition between micellar stretching and scission under uniaxial extensional flow. We further propose a relation that connects the extensional viscosity to micellar structures and kinetics. This relation provides a unified description of the extensional viscosity of unentangled wormlike micellar solutions for various temperatures, concentrations, and extension rates.

cond-mat.soft↗

arXiv2025

Direct observation of the compression behavior of polystyrene microbeads in a diamond anvil cell

The pressure dependence of the bulk modulus of glassy polystyrene (PS) was measured in the relatively high-pressure regime, up to 6 GPa, at ambient temperature. For the measurements, PS microbeads were immersed in a pressure medium consisting of a mixture of methanol and ethanol, and the sample was placed in a diamond anvil cell capable of generating high and hydrostatic pressure. The volume change of the PS beads was observed under an optical microscope. The results demonstrated that the volume change in this study is consistent with an equation of state determined from the earlier studies in the low-pressure range up to 0.2 GPa. The bulk modulus was obtained as the derivative of the microbead volume with respect to pressure, and compared with the earlier data obtained from Brillouin spectroscopy.

cond-mat.soft↗

arXiv2025

Effects of Stirring Time on Formation of Microplastics Fragmented from Photo-aged Polypropylene

This paper examines the evolution of microplastic (MP) size distributions fragmented from photo-aged polypropylene (PP) in stirred water. PP specimens fragmented into MPs with their size of 1-30 um after UV irradiation and stirring in laboratory settings. These laboratory-fragmented MPs were dispersed into the water during the stirring process. A series of MP size distributions was analyzed from optical microscope images of obtained MPs. The MP size distribution was described by an exponential function in the short stirring time domain, whereas it changed to a power-law function as the stirring time increased. The fragmentation rate of MPs and nanoplastics (NPs) decreased with increasing stirring time. The obtained MP exhibited higher crystallinity than the photo-aged PP specimen after stirring. This result implies that MP fragmentation, as observed under controlled laboratory conditions, is related with the chemi-crystallization of PP.

cond-mat.soft↗

arXiv2025

Nonmonotonic concentration dependence of the self-diffusion coefficient of surfactants in wormlike micellar solutions

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.

cond-mat.soft↗

arXiv2025

Coarse-Grained Molecular Dynamics Simulations for Oxidative Aging of Polymers under Various O2 Concentration

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_2) to reflect the effects of the O2 concentration. Three key aspects of oxidative aging behavior were found to be influenced by the O2 addition rate: (i) reaction kinetics, (ii) the degree of heterogeneity, and (iii) amount of crosslinking. Namely, reducing O2 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.

cond-mat.soft↗