Flow-Induced Disentanglement in Shear and Elongational Flows of Entangled Polymers: A Hi-Fidelity Molecular Simulation Study

主要研究者：Edwards，BrianProposal编号：1602890拟议研究的目标是了解大分子（如聚合物或蛋白质）的行为以及当流体速度较高时这些大分子纠缠和解开的方式。虽然这是一个可以通过分子尺度上的观察来回答的基本问题，但它可能具有在石化和食品工业中常见的流体的处理期间重要的显著宏观效应，例如，聚合物、表面活性剂和液晶。人们提出了许多理论来解释这些复杂液体在流动条件下的微观结构响应，但每一种理论都与高应变率下的实验结果大相径庭。最近的证据表明，这些分歧的部分原因是，大多数流动模型跟踪批量平均性能，有效地丢弃了单个分子的短时间尺度的动力学现象。最近通过适度缠结的聚乙烯液体的非平衡分子动力学（NEMD）模拟观察到，在剪切和拉伸流动中在高应变率下发生显著的动力学响应：聚合物液体经历链缠结数量的显著减少，这导致了一个高度拉伸的链网络，形成了有效的管，类似于相邻链经历各向异性扩散的结构。在剪切主导的流动中，这最终导致链旋转和收缩循环，其产生比液体的蠕动时间短得多的特征时间尺度。该项目将使用一套前所未有的NEMD和耗散粒子动力学（DPD）模拟聚乙烯液体（每条链多达50个缠结）来研究这种行为。此外，所获得的知识将收获开发一个介观各向异性扩散模型，可应用于高应变率流。所提出的工作的结果可能有助于更有效地建模现有的过程和新的流体材料的设计，或制造它们的过程。 这项工作产生的数据将通过PolyHub存储网站提供给研究界。还计划开展外联和教育活动，包括制定教育单元。

PI: Edwards, BrianProposal Number: 1602890The goal of the proposed research is to understand the behavior of macromolecules (like polymers or proteins) and the way that these macromolecules get entangled and disentangled when the fluid velocity is high. While this is a fundamental problem that can be answered by observations at the molecular scale, it can have significant macroscopic effects that are important during the processing of fluids common in the petrochemical and the food industry, e.g., polymers, surfactants, and liquid crystals.Many theories have been proposed to explain the microstructural responses of these complex liquids under flow, but each invariably diverged from experiment at high strain rates. Recent evidence suggests that part of the reason for these divergences is that most flow models track bulk-average properties that have effectively discarded the short-timescale dynamical phenomena of the individual molecules. It has recently been observed via nonequilibrium molecular dynamics (NEMD) simulations of moderately-entangled polyethylene liquids that a remarkable dynamical response occurs at high strain rates in both shear and elongational flows: the polymeric liquid experiences a dramatic decrease in the number of chain entanglements, which leads to a network of highly-stretched chains that form effective tube-like structures through which neighboring chains experience anisotropic diffusion. In shear dominated flows, this ultimately leads to chain rotation and retraction cycles, which give rise to characteristic timescales that are much shorter than the reptation time of the liquid. This project will study this behavior using an unprecedented suite of NEMD and Dissipative Particle Dynamics (DPD) simulations of polyethylene liquids with up to 50 entanglements per chain. In addition, the knowledge gained will be harvested to develop a mesoscopic anisotropic diffusion model that can be applied to high strain-rate flows. Results of the proposed work could contribute to more efficient modeling of existing processes and to the design of new fluid materials, or the processes to manufacture them. Data resulting from this work will become available to the research community through the PolyHub storage site. There are also outreach and education activities planned that involve the development of educational modules.