Yuya Doi

Yamagata University | YU · Department of Organic Materials Science

Polymer architecture (i.e., chain connecting manner) and properties are closely correlate, and strongly influence rheological properties that reflect microscopic molecular dynamics. This review summarizes the rheological properties of ring polymers and polymers containing intramolecular loops, which are currently being studied actively in terms of...

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 u...

I have learned a lot in my life as a researcher (especially after obtaining my Ph.D.) by changing my environment. In this article, I introduce some of my experiences so far.

In this study, we investigated polymer chain dimensions in solid polymer electrolytes (SPEs) composed of hydrogenated and deuterated poly(ethylene carbonate/ethylene oxide) (h-/d-P(EC/EO)) copolymers and lithium bis(trifluoromethane)sulfonimide (LiTFSI) at various lithium-ion concentrations. The results were compared with h/d-poly(ethylene oxide) (...

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...

Most lithium batteries offer a wide range of applications. However, safety issues are still an unresolved issue for several applications. To solve the safety issue of Li-ion batteries, solid polymer electrolyte is a promising candidate to replace commercial liquid electrolyte. A 4-arm star poly(ethylene oxide) polymer with LiTFSI salt as an electro...

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...

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 di...

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 auto-oxidation mechanism, which is initiated by radicals, leading to the chain scission and crosslinking of polymer chains. In this study, we integrate a thermal oxidation...

The influence of node functionality (f) on the fracture of polymer networks remains unclear. While many studies have focused on multi-functional nodes with f>4, recent research suggests that networks with f=3 exhibit superior fracture properties compared to those with f=4. To clarify this discrepancy, we conducted phantom chain simulations for star...

During bulk free-radical polymerization of methyl methacrylate below the glass-transition temperature of poly(methyl methacrylate), the relative fraction of monomer and polymer changes as the reaction proceeds. The liquid monomer is eventually converted to a solid glassy polymer. In other words, polymerization-induced vitrification or glass transit...

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...

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 i...

We develop a novel Moving Particle Simulation (MPS) method to accurately reproduce the motion of fibers floating in sheared liquids. 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...

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. Here, we investigate a mobile rod-like particle in a three-dimensional sea of immobile...

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 con...

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...

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 ch...

Some components in colloidal suspensions, biological systems, active matters, and polymeric materials exhibit time-dependent diffusivity, called the fluctuating diffusivity. The fluctuating diffusivity has been attributed to two origins: a temporarily and/or spatially heterogeneous environment, or a fluctuation of a conformation of a component. In...

We investigated the terminal relaxation behavior of entangled linear polystyrene L430 (with the entanglement number Z = M/Me ≃ 24, where M is the molecular weight and Me is the entanglement molecular weight) blended with ring R30 (MR ≃ 1.8 Me) and dumbbell-shaped D308030 (MR ≃ 1.8 Me and ML ≃ 4.7 Me) polymers. The L430/R30 blend exhibits a one-step...

Mixtures of poly(vinylidene difluoride-co-hexafluoropropylene) (PVDF-HFP) and ionic liquids (IL) are known to form flexible, self-healing, and ion-conductive materials that are often referred to as polymer–gel electrolytes. The ion–dipole interaction occurs between PVDF-HFP and the cation; that is, the IL acts not only as a solvent but also as a tr...

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 t...

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 con...

A concentration gradient is induced by a temperature gradient for some binary mixtures of fluids due to the mass transfer. This phenomenon is the so-called thermodiffision or the Ludwig-Soret effect being characterized by the mass and heat cross transport coefficient L1q. Naively, we expect that L1q is controlled by the chemical potential. Then the...

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 st...

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. B...

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 primi...

The linear viscoelastic properties of poly(propylene carbonate) (PPC) melts having different molecular weights and narrow molecular weight distributions were studied. Some linear viscoelasticity parameters, including the plateau modulus and zero shear viscosity of PPC, were evaluated. The entanglement molecular weight of PPC was estimated to be 5.9...

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 s...

Diblock copolymers consisting of flexible polystyrene and semiflexible poly(n-hexyl isocyanate), P(S-b-HIC)s, were prepared by anionic polymerization, followed by size-exclusion chromatography (SEC) fractionation. Two P(S-b-HIC) samples having PHIC volume fractions (ΦPHIC) of 0.18 and 0.31, sufficiently high molecular weights (Mn,PS and Mn,PHIC are...

Although it has been established that the multi-chain slip-spring (MCSS) model can reproduce entangled polymer dynamics, the effects of model parameters have not been fully elucidated yet. In this study, we systematically investigated the effects of slip-spring density. For the diffusion and the linear viscoelasticity, the simulation results exhibi...

In some literature, entanglement molecular weight Me is discussed as a material property that characterizes magnitudes of entanglement for polymeric liquids. However, Me was introduced as a model parameter for theories that explain the plateau modulus, and the value is model dependent. A value of Me may induce misleading analysis if it is presented...

In this study, linear melt rheology of a single-tail tadpole-shaped polystyrene, ST-30/80, having ring and linear sizes of MR ~ 30 kg/mol and ML ~ 80 kg/mol, respectively was examined, and the effect of the ring size on the rheological properties of tadpole polymers was discussed by comparing with the data of the tadpole samples having MR ~ 60 kg/m...

A four‐branched cage‐shaped poly(ethylene oxide) (4C‐PEO) was prepared by a coupling reaction at very dilute condition between two kinds of end‐functional four‐armed star‐shaped PEOs having amino and N ‐hydroxysuccinimide groups on their four ends, followed by purification using α ‐cyclodextrin (α ‐CD). The raw coupling reaction product shows multi...

The non-linear viscoelastic response under interrupted shear flows is one of the interesting characteristics of entangled polymers. In particular, the stress overshoot in the resumed shear has been discussed concerning the recovery of the entanglement network in some studies. In this study, we performed multi-chain slip-link simulations to observe...

Conformations of highly purified ring polystyrene, R-70, with the molar mass of 70 kg/mol, in a good solvent and in linear polymer homologue matrices were examined by small-angle neutron scattering (SANS) measurements. The radii of gyration Rg of R-70 were estimated by the Guinier’s approximation from the SANS profiles obtained, and the polymer vol...

Highly purified hydrogenous ring poly(4-trimethylsilylstyrene) (h-PT) and deuterated ring polyisoprene (d-PI) samples as well as their linear counterparts were prepared, and the miscibility of three kinds of polymer blends, i.e., linear–linear, ring–linear, and ring–ring, denoted as L–L, R–L, and R–R, respectively, with all 50/50 vol % was evaluate...

We prepared five pairs of hydrogenous and deuterated ring polystyrene samples over a wide range of molecular weights (10 kg/mol ≤ Mw ≤ 400 kg/mol) and investigated their chain conformations in bulk by small-angle neutron scattering (SANS) measurements. From the SANS profiles obtained, we estimated the radii of gyration Rg of the ring polymers by th...

For high-molecular-weight (M) ring polymers with low contamination of linear chains, recent viscoelastic tests revealed broad terminal relaxation associated with no clear entanglement plateau. This relaxation behavior is qualitatively similar to that deduced from molecular models (double-folded lattice-animal model and the fractal loopy globule mod...

Understanding of the properties of ring polymers is one of the central subjects in polymer physics. Thanks to the development in separation and purification techniques of ring polymers, highly-purified ring polymers could be prepared, and the studies on ring polymers have progressed. In this article, we briefly summarize recent discoveries of physi...

A dumbbell-shaped polystyrene (PS) sample, where rings are attached on both ends of a linear chain, was anionically synthesized by a coupling reaction between highly-purified ring PS (R-30; Mw = 33.7 kg/mol) with two diphenylethylene (DPE) type vinyl groups and bifunctional living linear PS (L-80; Mw = 84.0 kg/mol). The crude coupling product obtai...

A series of comb-shaped ring polystyrene samples, RC, composed of a common ring backbone and multiple linear branches with three different lengths were successfully prepared. First, a highly purified ring backbone was synthesized by anionic polymerizations followed by multistep size exclusion chromatography (SEC) and interaction chromatography (IC)...

A series of highly purified tadpole-shaped polystyrene (PS) samples were prepared by anionic polymerizations and multistep HPLC fractionations, and their linear melt rheology was investigated. Three tadpole samples were composed of a common ring chain (R-60; Mw = 59.8 kg/mol) and three different lengths of linear chains (L-30, L-70, and L-120; Mw =...

The melt rheology of highly-purified ring polystyrenes in a wide range of molecular weights (10K ≤ Mw ≤ 240K g/mol) was investigated. All the rings revealed no obvious rubbery plateau and faster terminal relaxation compared to the linear counterparts. The rheological data obtained were compared with some theoretical models such as the Rouse ring mo...

Tadpole-shaped polystyrenes (PS) were successfully synthesized anionically by coupling reaction between ring polystyrene with two functional groups and living linear polystyrenes. Crude coupling product was confirmed to include unreacted linear tail polymer and tadpole polymer having one tail (single-tail tadpole polymer) and two tails (twin-tail t...