Department of Physics and Biophysics, University of San Diego, 5998 Alcala Park, San Diego, CA 92110, USA.
Soft Matter. 2024 Nov 13;20(44):8909-8923. doi: 10.1039/d4sm01065e.
Blends of circular and linear polymers have fascinated researchers for decades, and the role of topology on their stress response and dynamics remains fervently debated. While linear polymers adopt larger coil sizes and form stronger, more pervasive entanglements than their circular counterparts, threading of circular polymers by linear chains can introduce persistent constraints that dramatically decrease mobility, leading to emergent rheological properties in blends. However, the complex interplay between topology-dependent polymer overlap and threading propensity, along with the large amounts of material required to sample many compositions, has limited the ability to experimentally map stress response to composition with high resolution. Moreover, the role of supercoiling on the response of circular-linear blends remains poorly understood. Here, we leverage enzymatic topological conversion to map the deformation dynamics of DNA blends with over 70 fractions of linear, ring and supercoiled molecules that span the phase space of possible topological compositions. We use OpTiDDM (optical tweezers integrating differential dynamic microscopy) to map strain-induced deformation dynamics to composition, revealing that strain-coupling, quantified by superdiffusive dynamics that are aligned with the strain, is maximized for blends with comparable fractions of ring and linear polymers. Increasing the supercoiled fraction dramatically reduces strain-coupling, while converting rings to linear chains offers more modest coupling reduction. We demonstrate that these results are a direct consequence of the interplay between increasing polymer overlap and decreasing threading probability as circular molecules are converted to linear chains, with a careful balance achieved for blends with ample ring fractions but devoid of supercoiled molecules.
环状和线状聚合物的共混物吸引了研究人员几十年的兴趣，拓扑结构对它们的应力响应和动力学的影响仍在激烈争论中。虽然线性聚合物采用更大的线圈尺寸，并形成比其环状对应物更强、更普遍的缠结，但线性链对环状聚合物的穿线可以引入持久的约束，从而显著降低其流动性，导致共混物中出现新的流变性质。然而，拓扑相关聚合物重叠和穿线倾向之间的复杂相互作用，以及需要大量材料来对许多成分进行采样，限制了以高分辨率将应力响应实验映射到成分的能力。此外，超螺旋对环状-线状共混物响应的作用仍未得到很好的理解。在这里，我们利用酶拓扑转化来绘制具有 70 多个线性、环状和超螺旋分子分数的 DNA 共混物的变形动力学，这些分子跨越了可能的拓扑组成的相空间。我们使用 OpTiDDM（光学镊子集成微分动态显微镜）将应变诱导的变形动力学映射到成分上，结果表明，应变耦合，由与应变一致的超扩散动力学来定量，对于具有相当比例的环状和线性聚合物的共混物达到最大值。增加超螺旋分数会显著降低应变耦合，而将环转化为线性链则会降低耦合程度。我们证明这些结果是由于环状分子转化为线性链时聚合物重叠增加和穿线概率降低的相互作用的直接结果，对于具有充足环状分数但没有超螺旋分子的共混物，达到了精细的平衡。
