Tumbling Acts: Conformational Dynamics and Interactions in Shear Flows of Semidilute Solutions

Understanding the properties of polymer solutions in flow are highly relevant for many applications ranging from 3D printing to polymer flow batteries. Because these properties often arise out of the molecular conformations and dynamics of the polymer, understanding how these change with design parameters such as flow strength and polymer concentration are highly pertinent. Previous work from our group developed a conformationally averaged Brownian dynamics simulation to explore how the presence of planar extensional flow in semi-dilute polymer solutions affected the conformational and rheological properties of the system and found interesting dynamics driven by the hydrodynamic interactions. Motivated by this work, we now want to consider how the non-equilibrium dynamics of polymer solutions are affected by shear flow - which in the dilute case has been shown to lead to interesting tumbling dynamics. We now seek to understand how not only these tumbling dynamics change by the presence of multiple interacting chains, but also the conformational and rheological properties of the polymer solution. In this work we will show that as the concentration is increased and flow is increased passed the coil-stretch transition, the extension of the polymers also increases due to increased obstructions from neighboring chains. Next, we show how the viscosity of such solutions display shear-thinning behavior; along with how the zero-shear viscosity scales with polymer concentration. Finally we will show how the characteristic time of tumbling decreases monotonically as the flow strength increases for low concentrations, but display an interesting non-monotonic behavior for higher concentrations. With this work, we have explored the interplay of concentration and flow strength in great detail to provide a molecular understanding of the design principles relevant for polymer solutions in shear flow.