Local Hydrodynamics and Chain Architecture in Flowing Semidilute Polymer Solutions*

It is important to understand the dynamics and rheology of semidilute polymer solutions at a molecular level, because out-of-equilibrium polymer conformations that arise due to strong processing flows can impact 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 crucial to capturing the dynamics of polymer solutions, both in and out-of-equilibrium. We developed an iterative conformational-averaging (CA) method for performing these calculations, circumventing a number of 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 hydrodynamics’ that enhance conformational fluctuations in planar elongational flows. HI is also shown to couple to polymer architecture, in both ring and branched polymers, in a variety of unexpected ways that have implications in conformational relaxation and polymer-polymer ‘hooking’.