(244f) Relaxation of Single Flexible Polymers

We report the direct observation of polymer chain relaxation for single flexible polymers using a combination of experiments and simulations. In this work, we studied the relaxation dynamics of flexible polymers based on single stranded DNA (ssDNA) following cessation of flow in tethered shear and planar extensional flow. We use single molecule fluorescence microscopy to characterize polymer chain relaxation from high stretch, and we present results for ssDNA chain relaxation as functions of time and polymer molecular weight. We compare results from experiments and Brownian dynamics simulations incorporating a low-force non-linear elastic relation appropriate for flexible chains with dominant excluded volume interactions. We explore the role of backbone flexibility on chain relaxation, and we determine dynamical scaling laws for ssDNA chain relaxation. In this way, our results highlight the differences in dynamics between “real” flexible polymers and “ideal” chains. Our work is enabled by the direct observation of truly flexible polymer chains using fluorescence microscopy. Recently, we developed a new experimental system for single molecule studies of flexible polymers based on ssDNA. The vast majority of single polymer studies have relied on double stranded DNA, a semi-flexible polymer with markedly different molecular properties compared to flexible polymer chains (dsDNA persistence length ≈ 60 nm; ssDNA persistence length ≈ 0.6 nm). We developed a biochemical synthesis platform for producing long strands of fluorescently-labeled ssDNA suitable for single polymer experiments. ssDNA molecules are synthesized to contain “designer” sequences, which avoid intrachain base pairing interactions. Using this approach, our work has extended single polymer experiments to a new class of materials. Our results will provide a molecular-based understanding of the non-equilibrium dynamics of flexible polymers, thereby enabling the development of advanced processing methods. 

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