Connecting polymer dynamics and Lagrangian flow structures in viscoelastic flows

In viscoelastic flows, the distribution of polymeric stress dictates the onset of elastic instabilities and material transport properties in a wide range of biological and industrial processes. However, measurements of the stress are often non-trivial even in steady flows, due to the intrinsic dependence of the polymer conformation upon the Lagrangian history of fluid deformation. In this work, we employ micro-PIV measurements of viscoelastic flows through a variety of canonical microfluidic geometries to elucidate the link between Lagrangian flow structure and polymer conformation. The measured Lagrangian fluid deformation is directly correlated with real-time imaging of single polymer kinematics in flow across a range of Weissenberg numbers. Our results are additionally compared to the theoretical polymer conformation and to stress fields from numerical simulations. Taken together, this work refines our Lagrangian perspective of viscoelastic flows by illustrating the relationship between fluid stretch and polymeric stress, and has implications for understanding their mixing and transport properties.