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Polymer dynamics in confined and concentrated media.

机译：在受限和浓缩介质中的聚合物动力学。

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In this work, we examine the dynamics of linear polymers under conditions where their movement is restricted, either by physical constraints or by the presence of other polymer molecules (such as in concentrated polymer solutions).;First, we use Brownian Dynamics and Monte Carlo techniques to simulate the behavior of polymer chains inside the ABEL trap (originally devised by Cohen et al. [Cohen and Moerner, 2006]). Subsequently, we employ Principal Component Analysis and image correlations to analyze their dynamics. Our analysis shows that confinement and backbone stiffness affect the most important modes of polymer conformation in chains with less than about five persistence lengths. Using longer chains, we reproduce the experimentally observed principal modes of lambda-DNA. Furthermore, using the Narrow Gaussian Potential form of excluded volume interactions, we examine the variation of the timescale of configuration correlations with solvent quality and chain length. We find that this timescale is linked to the polymer diffusion timescale and that the presence of confining walls causes it to vary more strongly with solvent quality.;Next, we investigate the behavior of entangled lambda-DNA solutions, well above the overlap concentration. Via rheometry, we find that these polymer solutions, like their synthetic counterparts, depict features such as a dip in the loss moduli and a plateau in the steady shear stress curve at intermediate frequencies and shear rates respectively. We also find that both shear and extensional stress increase linearly with the imposed deformation rate in strong flows and are also able to measure overshoots in the viscosity during startup of shear flow. Using single molecule techniques, we show that molecules in the concentrated regime can be stretched in a planar extensional flow in a microdevice. The subsequent relaxation process of these stretched molecules is observed to be much slower than the dynamics in the dilute regime, presumably due to the presence of entanglements.;Finally, we develop a slip-link based simulation technique, based on the work by Masubuchi et al. [Masubuchi et al., 2001], to directly simulate the motion of individual polymer strands in an entangled solution. Using this method, we reproduce the variation of the disengagement time with entanglement number and also replicate the experimentally observed variation of spectral power with frequency [Teixeira et al., 2007]. Also in accordance with single molecule experiments, we observe wide distributions of polymer stretch and orientation along with incomplete alignment even in strong flows. Furthermore, using these same simulations, we find that constraint release events, which affect the configuration of our network, cause the emergence of the plateau in steady shearing flows. To simulate these systems in extension dominated flows, we refine this technique using an implicit-form of the governing stochastic differential equations. By doing so, we are able to impose planar extensional flow and measure the corresponding viscosity curve which shows a thinning region before the onset of extension hardening.
机译：在这项工作中，我们研究了在线性运动受到物理约束或存在其他聚合物分子（例如在浓缩的聚合物溶液中）的限制下线性聚合物的动力学。首先，我们使用Brownian Dynamics和Monte Carlo技术模拟ABEL陷阱内聚合物链的行为（最初由Cohen等人设计[Cohen and Moerner，2006]）。随后，我们采用主成分分析和图像关联来分析其动力学。我们的分析表明，约束和骨架刚度影响着少于约5个持久长度的链中聚合物构象的最重要模式。使用更长的链，我们重现了实验观察到的lambda-DNA的主要模式。此外，使用排除体积相互作用的窄高斯势形式，我们研究了与溶剂质量和链长相关的构型相关时间尺度的变化。我们发现该时间尺度与聚合物扩散时间尺度相关，并且限制壁的存在导致其随溶剂质量的变化更大。;接下来，我们研究了纠缠的λ-DNA溶液的行为，该行为远高于重叠浓度。通过流变法，我们发现这些聚合物溶液，与它们的合成对应物一样，分别表现出诸如损耗模量的下降和稳态剪切应力曲线在中频和剪切速率下的平稳状态。我们还发现，在强流中，剪切应力和拉伸应力都随施加的变形率线性增加，并且还能够在剪切流启动期间测量粘度的过冲。使用单分子技术，我们证明了在浓缩状态下的分子可以在微型设备中的平面延伸流中被拉伸。可能是由于纠缠的存在，观察到这些拉伸分子随后的松弛过程比动力学中的动力学要慢得多；最后，我们基于Masubuchi等人的工作开发了一种基于滑环的模拟技术。等[Masubuchi et al。，2001]，直接模拟缠结溶液中单个聚合物链的运动。使用这种方法，我们再现了脱离时间随纠缠数的变化，并且还复制了实验观察到的频谱功率随频率的变化[Teixeira et al。，2007]。同样根据单分子实验，我们观察到即使在强流动中，聚合物的拉伸和取向分布也很宽，而且排列不完全。此外，使用这些相同的模拟，我们发现约束释放事件影响了网络的配置，导致稳定剪切流中平台的出现。为了在扩展支配流中模拟这些系统，我们使用控制随机微分方程的隐式形式改进了该技术。这样，我们就可以施加平面延伸流，并测量相应的粘度曲线，该曲线显示在延伸硬化开始之前的变薄区域。

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