Ring polymers exhibit unique flow properties due to their closed chain topology. Despite recent progress, we have not yet achieved a full understanding of the nonequilibrium flow behavior of rings in nondilute solutions where intermolecular interactions greatly influence chain dynamics. In this work, we directly observe the dynamics of DNA rings in semidilute ring-linear polymer blends using single molecule techniques. We systematically investigate ring polymer relaxation dynamics from high extension and transient and steady-state stretching dynamics in a planar extensional flow for a series of ring-linear blends with varying ring fraction. Our results show multiple molecular subpopulations for ring relaxation in ring-linear blends, as well as large conformational fluctuations for rings in a steady extensional flow, even long after the initial transient stretching process has subsided. We further quantify the magnitude and characteristic time scales of ring conformational fluctuations as a function of blend composition. Interestingly, we find that the magnitude of ring conformational fluctuations follows a nonmonotonic response with increasing ring fraction, first increasing at low ring fraction and then substantially decreasing at large ring fraction in ring-linear blends. A unique set of ring polymer conformations are observed during the transient stretching process, which highlights the prevalence of molecular individualism and supports the notion of complex intermolecular interactions in ring-linear polymer blends. In particular, our results suggest that transient intermolecular structures form in ring-linear blends due to a combination of direct forces due to linear chains threading through open rings and indirect forces due to hydrodynamic interactions; these combined effects lead to large conformational fluctuations of rings over distributed time scales. Taken together, our results provide a new molecular understanding of ring polymer dynamics in ring-linear blends in the nonequilibrium flow.

中文翻译：

---

拉伸流中环状线性混合半稀溶液的动力学和流变学：单分子实验

环状聚合物由于其闭链拓扑结构而表现出独特的流动特性。尽管最近取得了进展，但我们尚未完全了解环在非稀溶液中的非平衡流动行为，其中分子间相互作用极大地影响链动力学。在这项工作中，我们使用单分子技术直接观察了半稀环状线性聚合物混合物中 DNA 环的动力学。我们从平面拉伸流中的高拉伸和瞬态和稳态拉伸动力学系统地研究了环状聚合物弛豫动力学，用于一系列具有不同环分数的环状线性混合物。我们的结果显示了环状线性混合物中环松弛的多个分子亚群，以及稳定拉伸流中环的大构象波动，即使在最初的瞬态拉伸过程消退很久之后。我们进一步量化了环构象波动的幅度和特征时间尺度作为混合成分的函数。有趣的是，我们发现环构象波动的幅度随着环分数的增加呈非单调响应，首先在低环分数时增加，然后在环线性混合物中在大环分数时显着降低。在瞬态拉伸过程中观察到一组独特的环状聚合物构象，这突出了分子个体主义的盛行，并支持了环状线性聚合物混合物中复杂的分子间相互作用的概念。特别是，我们的结果表明，由于线性链穿过开环产生的直接力和流体动力相互作用产生的间接力的组合，在环-线性混合物中形成了瞬态分子间结构；这些综合效应导致环在分布式时间尺度上的大的构象波动。综上所述，我们的结果提供了对非平衡流动中环状线性混合物中环状聚合物动力学的新分子理解。