Dynamics of DNA-Bridged Dumbbells in Concentrated, Shear-Banding Polymer Solutions
Dynamics of DNA-Bridged Dumbbells in Concentrated, Shear-Banding Polymer Solutions
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DNA 桥哑铃在浓缩剪切带聚合物溶液中的动力学
DOI：
10.1021/acs.macromol.0c02890
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发表时间：
2021
期刊：
影响因子：
5.5
通讯作者：
Cheng, Xiang
中科院分区：
文献类型：
--
作者：
Shin, Seunghwan;Kou, Yangming;Dorfman, Kevin D.;Cheng, Xiang
尽管在过去的20年里，在浓聚聚合物溶液中剪切带流动的实验证据已经积累起来，但这种剪切带流动的起源仍然存在激烈的争论。探索剪切带聚合物溶液微观动力学的实验仍然很少。在这里，我们使用定制的高分辨率流变共聚焦剪切细胞，实验研究了DNA桥接胶体哑铃在大振幅振荡剪切下在浓缩双链DNA （dsDNA）溶液的剪切带流动中的动力学。我们合成了由λ-DNA连接的两个球形胶体组成的哑铃，并在剪切的dsDNA溶液中跟踪它们的二维投影构型。我们首先证实了高浓度dsDNA溶液的速度分布在高Weissenberg数下是不均匀的，并且表现出强烈的剪切带，有两个明显的剪切带。然后，我们测量了dna桥接哑铃的方向分布，并研究了它们在两个剪切带内的平移和旋转动力学。在高剪切率带中，哑铃沿流动方向的优先排列表明弹性应力在该带中起主导作用。相反，在低剪切速率带观察到哑铃方向的双峰分布，表明法向和弹性应力的贡献更为平衡。此外，仅在高剪切速率波段，我们还发现了空间局部相关的增强平移和旋转运动，以及增强平移和链延伸之间的强耦合。这些独特的构象和动力学特征表明，剪切导致高剪切带中局部纠缠网络的断裂，我们假设这导致了高粘度流体中低粘度的水坑。总之，我们对共存剪切带中dsdna桥接哑铃的空间不同动力学的定量分析为深入了解浓缩聚合物溶液中剪切带流动的微观起源提供了重要见解。
Although experimental evidence for shear-banding flows in concentrated polymer solutions has accumulated over the last 20 years, the origin of such shear-banding flows is still under heated debate. Experiments that probe the microscopic dynamics of shear-banding polymer solutions are still scarce. Here, using a custom-built high-resolution rheo-confocal shear cell, we experimentally study the dynamics of DNA-bridged colloidal dumbbells in the shear-banding flow of concentrated double-stranded DNA (dsDNA) solutions under large amplitude oscillatory shear. We synthesize dumbbells consisting of two spherical colloids linked by λ-DNA and track their 2D-projected configurations in sheared dsDNA solutions. We first confirm that the velocity profile of the concentrated dsDNA solutions is inhomogeneous at high Weissenberg numbers and exhibits strong shear banding with two distinct shear bands. We then measure the orientational distribution of the DNA-bridged dumbbells and investigate their translational and rotational dynamics within the two shear bands. The preferred alignment of the dumbbells along the flow direction in the high-shear-rate band suggests the dominant role of elastic stresses in that band. In contrast, a bimodal distribution of dumbbell orientations is observed in the low-shear-rate band, indicating more balanced contributions from both normal and elastic stresses. Furthermore, exclusively in the high-shear-rate band, we also find spatially localized correlated enhanced translational and rotational motions and a strong coupling between enhanced translation and chain extension. These unique conformational and dynamic features suggest shear-induced breakage of the local entanglement network in the high-shear band, which we postulate leads to puddles of low viscosity within an otherwise high-viscosity fluid. Together, our quantitative analyses of the spatially distinct dynamics of dsDNA-bridged dumbbells in coexisting shear bands provide important insights into the microscopic origin of shear-banding flows in concentrated polymer solutions.
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