Disentangling the dynamics of shear banding in entangled polymer solutions

解开缠结聚合物溶液中剪切带的动力学

• 批准号: 1700771
• 负责人: Xiang Cheng
• 金额: $ 35.74万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2021-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1700771&HistoricalAwards=false
• 关键词: Disentangling; dynamics; shear; banding; entangled; Disentangling; dynamics; shear; banding; entangled

Plastics are ubiquitous to modern society, used in food packing, electronic devices, transportation, sports equipment, and medical devices. The precursor to all formed plastics is a polymer fluid. Polymer fluids are a unique type of fluid, as the chain-like polymer molecules act like springs, and within a collection of fluid molecules, the polymer springs become entangled. Unlike water and many other fluids, this complex fluid does not respond to the forces of stress and shear in a manner that is proportional to the applied force. This non-proportional response is classified as Non-Newtonian. Non-Newtonian fluids have not been adequately described by general engineering models of fluid flow. Without general models, prediction of flow in industrial processing is limited to trial-and-error. Under some circumstances, such as slow flow or low concentration, many of these complexities can be ignored. However, these are not the most industrially relevant conditions, where high concentration and fast flow are prevalent. This project supports a fundamental experimental study on the fast flow of concentrated polymer fluids, and uses state-of-the-art imaging techniques to directly image single polymer molecules to reveal the microscopic dynamics of complex fluid flow. The challenge in understanding the dynamics of concentrated polymer fluids is the nonlinear viscoelasticity of entangled polymer solutions, particularly the formation of shear-banding in concentrated polymer solutions at high shear rates. These phenomenon are difficult to probe experimentally. This research project combines high-speed confocal microscopy with a custom shear cell to investigate the origin of shear-banding flows of a model system, namely, concentrated DNA solutions. The applications of these unique experimental tools to the problem will resolve a controversy regarding on shear-banding in polymer fluids. The phase diagram of the shear-induced dynamics of concentrated DNA solutions is being mapped. The project aims to establish a direct link between the microscopic dynamics of DNA molecules and the macroscopic flow behavior of polymer fluids. The project is elucidating the dynamics of single polymer molecules in concentrated solutions under fast shear and experimentally validating competing theories on shear banding of polymer fluids. These results are uncovering the missing theoretical understanding of concentrated polymer fluids under fast flows and, ultimately, practical engineering models for polymer fluids under the most industrially relevant conditions. Increased control and prediction of polymer flow will increase throughput and efficiency, and therefore greatly impact the U.S. manufacturing sector. This research project also involves K-12 outreach programs with local high school students, especially those underrepresented in science and engineering.

塑料对现代社会无处不在，用于食品包装，电子设备，运输，运动器材和医疗设备。 所有形成的塑料的前体是聚合物流体。 聚合物流体是一种独特的流体类型，因为链状聚合物分子像弹簧一样起作用，并且在流体分子的集合中，聚合物弹簧被纠缠在一起。 与水和许多其他流体不同，这种复杂的流体不会以与施加力成正比的方式对压力和剪切力的反应。这种非比例响应被归类为非牛顿。 流体流的通用工程模型尚未充分描述非牛顿流体。 没有一般模型，工业处理中流量的预测仅限于反复试验。在某些情况下，例如流量缓慢或浓度较低，许多这些复杂性都可以忽略。但是，这些不是最相关的条件，在高浓度和快速流动的情况下。该项目支持对浓缩聚合物流体快速流动的基本实验研究，并使用最先进的成像技术直接成像单聚合物分子来揭示复杂流体流的微观动力学。理解浓缩聚合物液的动力学的挑战是纠缠聚合物溶液的非线性粘弹性，尤其是以高剪切速率在浓缩聚合物溶液中形成剪切带的形成。这些现象很难实验探测。该研究项目将高速共聚焦显微镜与自定义剪切电池结合起来，以研究模型系统的剪切带的起源，即浓缩DNA溶液。这些独特的实验工具在问题上的应用将解决有关聚合物液中剪切的争议。剪切诱导的浓缩DNA溶液动力学的相图正在映射。该项目旨在建立DNA分子的显微镜动力学与聚合物流体的宏观流动行为之间的直接联系。该项目正在阐明在快速剪切下浓缩溶液中单个聚合物分子的动力学，并实验验证了聚合物液的剪切条带的竞争理论。这些结果揭示了在快速流动下对集中聚合物流体的理论理解，并最终在最相关的条件下为聚合物流体提供了实用的工程模型。对聚合物流的控制和预测的增加将提高吞吐量和效率，因此极大地影响了美国制造业。该研究项目还涉及与当地高中生的K-12外展计划，尤其是科学和工程领域的人数不足的学生。