Brownian dynamics simulations of linear and non-linear semidilute polymer solutions in extensional flow

Understanding the relationship between microstructure and bulk properties is an overarching goal in polymer rheology. This is particularly true for non-linear polymer architectures, where topological interactions resulting from chain crossing restrictions lead to flow rates which are locally much higher than the applied flow. Polymers can thus be deformed significantly from their expected conformations, modifying the molecular functionality and the bulk stress. Coarse-grained molecular simulations which satisfy crossing constraints are crucial for developing quantitative models of these phenomena. Using our iterative conformational averaging method for Brownian dynamics simulations, we present an explanation for unexpected dynamics in solutions of non-linear polymers first observed in single molecule imaging experiments. Starting from a solution of linear chains, we introduce trace ring or branched polymers and observe the effect on polymer relaxation and transient stretching in planar extensional flow. We determine the importance of hydrodynamic interactions for polymer solutions ranging from dilute to the entanglement concentration and show that non-linear polymers can exhibit accelerated or hindered relaxation below the overlap concentration.