The role of hydrodynamics in flowing semidilute solutions of ring/linear polymer blends*

It is important to understand the dynamics of semidilute polymer solutions at a molecular level, because out-of-equilibrium polymer conformations that arise due to strong processing flows can impact both rheology and eventual material properties in a variety of applications. Despite this practical importance, it remains a challenge to predict how concentration, flow, hydrodynamic interactions (HI) and architecture all govern the dynamics of semidilute polymer solutions. This is particularly true in simulation, where it is computationally expensive to include long-range HI effects that are necessary to accurately model the dynamics of polymer solutions. We developed an iterative conformational-averaging (CA) method for performing these calculations, circumventing computational bottlenecks to enable the large-scale simulation of polymer solutions in flow. CA calculations demonstrate the importance of HI in semidilute solutions, revealing the effect of 'local flows' that enhance conformational fluctuations. We demonstrate these effects in the context of ring/linear blends, where there is a competition between topological 'hooking' and chain length effects that showcase the complicated role of polymer architecture in conformational dynamics during both startup and steady-state flows.