Multiscale simulations for polymer melt spinning process using Kremer–Grest CG model and continuous fluid mechanics model

We succeeded in developing a multiscale simulation (MSS) method for a spinning process of a polymer melt. A previous work by Sato and Taniguchi (2017) developed a MSS method where the microscopic model and macroscopic model for the spinning process are respectively modeled by using a slip-link model and a continuous fluid mechanics model. Here we replace the microscopic model with the Kremer–Grest coarse-grained (CG) model, and investigate the state of the polymer chains at steady state in the spinning process, by changing the draw ratio Dr. Unlike the previous MSS, where the microscopic simulator is a slip-link model, in which polymer chains are simulated in virtual space and entanglements are treated by virtual links, in the present MSS, a real space molecular dynamics simulator is used as the microscopic simulator. The replacement brings the advantage that we can obtain more information on the state of polymer chains, but also brings two computational difficulties, (I) the requirement of a huge computational cost, and (II) the simulation box problem related to the periodic boundary condition in the microscopic system. To deal with (I), we considered a micro-macro coupling method different from previous MSS. To resolve problem (II), we used the UEF (uniform extensional flow) method developed by Nicholson and Rutledge (2016) and Murashima et al. (2018) for a polymer melt system. By using these two ideas, we performed MSS simulations, and established a correspondence between the macroscopic flow and the microscopic polymer conformations at any position along the spinning line. Furthermore, we investigated the influence of Dr on the stretching and orientation of polymers chains and the spatial correlation between polymer chains.