[SY-H8] Relation between Macroscopic Flows in a Contraction-Expansion Channel and Dynamics of Well-Entangled Polymer Chains
We have successfully applied a multiscale simulation (MSS) method [T. Murashima and T. Taniguchi, Europhys. Lett., 96, 18002 (2011)] to flows of a monodispersed linear entangled polymer melt in a contraction-expansion channel. In our MSS method, a macroscopic model based on the Lagrangian picture is coupled with a microscopic polymer model through the velocity gradient tensor and the stress tensor. The smoothed particle hydrodynamics (SPH) method is employed as the macroscopic model, and the slip-link model [M. Doi and J. Takimoto, Phil. Trans. R. Soc. Lond A, 361, 641 (2003)] is employed as the microscopic model. Two-dimensional flows of a well-entangled polymer melt in a 4:1:4 contraction-expansion channel are examined using our MSS method. From our MSSs, we have investigated both macroscopic and microscopic information. As for the macroscopic information, we have focused on the spatial-dependent Weissenberg number (Wi). As for the microscopic information, we have evaluated the local orientation of polymer chains, the spatial distribution of the average number of entanglements and the number density of entanglements along a polymer chain. The states of the polymer chains are altered mainly in the region corresponding to Wi > 1. In this region, we have confirmed that the polymer chains are strongly oriented, the average number of entanglements decreases and the number density of entanglements decreases in the center part on the polymer chain and has peaks near the tails. Furthermore, we have examined the number density of entanglements along a polymer chain in detail. From an analysis of the number density of entanglements, we have found that an effective advection and a hooking event play an important role in forming the number density of entanglements. Microscopic information obtained by our MSSs will provide us with new insights for the molecular design of a polymer chain.