Single molecule techniques allow for the direct observation of polymer dynamics in highly non-equilibrium conditions. Until recently, however, these methods have been largely confined to linear DNA molecules as ‘model’ polymer chains. In this talk, I will discuss recent work from our group in extending the field of single polymer dynamics to broader classes of materials, including branched polymers, ring polymers, and semi-dilute solutions. In this way, we explore new questions in classical polymer physics such as the role of architecture and interchain interactions on dynamics at the molecular level. In the first part of the talk, I discuss our recent work in directly visualizing DNA-based comb polymers. Macromolecular DNA combs are synthesized utilizing a hybrid enzymatic-synthetic approach, wherein chemically modified DNA branches and DNA backbones are generated in separate polymerase chain reactions, followed by a graft-onto reaction via click chemistry. This method allows for the synthesis of dual-color DNA combs, such that the backbone and side branches can be tracked independently using single molecule fluorescence microscopy. In this way, we study the dynamic properties of single comb polymers under flow, including conformational relaxation and stretching dynamics for highly branched chains. In the second part of the talk, I will discuss our recent work in visualizing polymer dynamics in semi-dilute solutions of linear chains in flow.
These results reveal a surprising dependence of interchain interactions for supposedly unentangled solutions, including rich molecular individualism that differs from dilute solution dynamics. I also present corresponding Brownian dynamics simulations of DNA in semi-dilute solutions, which show good agreement with experimental data. Overall, our work highlights the power and utility of using single molecule methods to study fundamental problems in polymer physics.