Visualizing single polymer conformation and dynamics using single-molecule optical microscopy

The behavior of single chains is integral to the foundation of polymer science. For example, many theories explaining fundamental behavior originate from how a single polymer interacts and responds to its environment, often made of other polymer chains. However, in this situation it is particularly difficult to visualize the behavior of single polymers, particularly because of the required nanoscale resolutions, and the lack of contrast between otherwise identical polymer chains. Our group uses single-molecule super-resolution optical microscopy to directly image the conformation and dynamics of polymers in real time and in their native environment. In one example, we acquire images of fluorescently-labeled bottlebrush polymers blended with an unlabeled linear polymer melt. By fitting these images to a wormlike chain model, we are able to accurately and directly measure the persistence length of the backbone for the first time. We also explore the dynamic behavior of these polymers under mechanical deformation. This addresses the fundamental question of how mechanical forces propagate to the nanoscale level of single polymer chains to alter their conformations and orientations. Finally, our single-molecule approaches are also applied to real-time tracking of diffusion in polyelectrolyte solutions and coacervates. Here our results highlight the importance of free volume in concentrated environments, an effect often overlooked in aqueous solutions.