(119f) Single Molecule Visualization of Ring Polymers in the Flow-Gradient Plane of Shear Flow

Ring polymers have fascinated polymer physicists for decades. Although the dynamic behavior of linear polymers is significantly affected by chain ends, ring polymers have a unique architecture without free ends, thereby resulting in qualitatively different flow dynamics compared to linear chains. Despite recent progress, we lack a clear understanding of the molecular-level dynamics of ring polymers in flow. Here, we use single molecule imaging to directly visualize individual ring polymers in the flow-gradient plane of shear flow. We designed and built a custom shear flow apparatus that enables the direct observation of DNA ring polymers in shear flow using single molecule fluorescence microscopy. In this way, we characterize the dynamics of single ring polymers in the flow-gradient plane of shear flow, including transient and steady fractional polymer extension and orientation angle of ring polymers in shear flow. We further compare the transient dynamics of ring polymers to their linear counterparts. In particular, we report the steady-state fractional extension, orientation angle, and temporal-averaged spatial conformations of ring polymers in shear flow as a function of the applied dimensionless flow strength (Wi, Weissenberg number), and compare these results to linear chains. We also report observations of tumbling behavior of ring polymers in shear flow. Our results show that ring polymers stretch differently than linear chains in shear flow, which is attributed to differences in the tumbling mechanism for ring versus linear chain architectures. Overall, these results provide new molecular-level insights into the dynamics of ring polymers in flow.