Flow-history-dependent behavior of entangled polymer melt flow analyzed by multiscale simulation

Polymer melts exhibit flow-history-dependent behavior. To clearly show this behavior, we have investigated the flow behavior of an entangled polymer melt around two cylinders placed in tandem along the flow direction in a two-dimensional periodic system. In this system, polymer states around a cylinder on the downstream side differ from those around a cylinder on the upstream side because the former have a memory of the strain they experienced when passing around the cylinder on the upstream side but the latter have no such memory. Therefore, the shear stress distributions around two cylinders are found to differ. Moreover, we have found that the mean flow velocity decreases accordingly with increasing distance between the two cylinders, whereas the applied external force is constant. Although this behavior is consistent with that of the Newtonian fluid, the flow-history-dependent behavior is found to enhance the reduction in the flow resistance. We have also discussed the microscopic states during the flow, observing the mean length of polymer chains, the mean number of entanglements, and the degree of orientation of polymer chains, which represented the flow-history-dependent behavior that reflects each relaxation process.