Yuichi Masubuchi 교수

A new model for Brownian dynamics simulations of entangled polymeric liquids is proposed here. Chains are coarse grained at the level of segments between consecutive entanglements; hence, the system is in fact a network of primitive chains. The model incorporates not only the “individual” mechanisms of reptation and tube length fluctuation, but also collective contributions arising from the 3D network structure of the entangled system, such as constraint release. Chain coupling is achieved by fu

Brownian dynamics simulations of the linear viscoelastic response of entangled polymers have been performed, and compared quantitatively with some existing solution data at a fixed concentration and variable molecular weight. The model is a three-dimensional network where the nodes are sliplinks connecting chains in pair. The simulations make use of Langevin equations both for the node motion in space, and for the one-dimensional monomer sliding through sliplinks. Comparison with data is very sa

To optimize automation for polymer processing, attempts have been made to simulate the flow of entangled polymers. In industry, fluid dynamics simulations with phenomenological constitutive equations have been practically established. However, to account for molecular characteristics, a method to obtain the constitutive relationship from the molecular structure is required. Molecular dynamics simulations with atomic description are not practical for this purpose; accordingly, coarse-grained mode

A novel simulation method that can calculate the long-time response of polymeric liquids in the entangled state is described. The polymer chain is replaced by a sequence of subchains connecting consecutive entanglements, called the 'primitive' chain. Collectively, the primitive chains form a rubberlike network, the nodes of which are the entanglements. The dynamics is modelled separately in two parts: motion of the entanglements in space and motion of monomers along the primitive chain (reptatio

Birefringence measurement demonstrates that the segment orientation of entangled polymers overshoots on start-up of fast shear [Pearson et al. <i>J. Rheol.</i> <b>1989</b> <i>33</i>, 517-535]. The stress-optical rule holds for those polymers, so that the overshoot of orientation results in the overshoot of shear stress. On the other hand, an opposite result was deduced from the recent molecular dynamics simulation for bead-spring chain [Lu et al. <i>ACS Macro Lett.</i> <b>2014</b> <i>3</i>, 569-

Recent simulations of entangled polymer dynamics are based on slip-link models pioneered by Hua and Schieber (J. Chem. Phys. 1998, 109, 10018). In this study, we compare different slip-link models in their prediction of the linear viscoelasticity of bidisperse linear polymers to examine how effectively such models account for constraint release. We compare the DT model by Doi and Takimoto (Philos. Trans. R. Soc. London, Ser. A 2003, 361, 641), the NS model by Nair and Schieber (Macromolecules 20

Entanglement dynamics of polymers under fast elongation has not been fully understood. Namely, the steady-state uniaxial elongational viscosity of entangled polystyrene (PS) solutions increases with an increase of strain rate above the reciprocal Rouse time, whereas the viscosity of PS melts monotonically decreases even at such high rates. This qualitative difference between solution and melt has been hypothesized to result from the orientation/stretch-induced reduction of friction (SORF). This

It is widely accepted that the nonlinear viscoelasticity of polymers with long chain branching can be described by the pom-pom theory [J. Rheol. 1998, 42, 81] that accounts for branchpoint withdrawal (BPW) as a nonlinear relaxation mechanism of the backbone. In spite of the remarkable success attained by refined theories derived from the original pom-pom model, there remain a few questions on the consistency with the theoretical development for linear polymers. For instance, convective constrain

Although the tube models have attained remarkable success, development of a simulation method for entangled branch polymer dynamics is still a challenge. In this study, the multichain slip-spring model has been examined to branch polymers for the first time. In the model, the bead–spring chains are dispersed in the simulation box, and the entanglement is mimicked by the virtual spring, so-called slip-spring, which connects the chains and hops along the chain. The slip-springs are created and des

Although lots of coarse-grained models have been proposed to trace the long-term behaviors of entangled polymers, compatibility among the different models has not been frequently discussed. In this study, some dynamical and static quantities, such as diffusion, relaxation modulus, chain dimension, and entanglement density, were examined for the multi-chain slip-link model (primitive chain network model) and the multi-chain slip-spring model, and the results were compared with those reported for

We have extended a recently developed multichain slip-spring approach to polymer solutions. The method is based on the dissipative particle dynamics (DPD). Entanglements are mimicked by the inclusion of slip-springs that connect polymer beads, slide along their contour, and are created/destroyed at chain ends. The required average number of slip-springs in polymer melts can be adjusted by the chemical potential. In solutions, we assume that the chemical potential and the friction of slip-springs