Molecular Motions in Flowing Semi-dilute Polymer Solutions

聚合物是大的链状分子，既是工业相关产品(如塑料、涂料和纤维)的基础，也是柔性光伏和显示器等设备的最先进材料。对于这些应用中的许多，聚合物的加工必须着眼于其最终性能；例如，为了制造出坚固的纤维，需要使用“拉伸”工艺来对齐聚合物链。同样，涂层流动可以控制半导体聚合物中的分子堆积(从而控制电荷传输)。在这两种情况下，聚合物都是通过施加强流在液体溶液中操纵的。然而，理解流动是如何影响分子运动的仍然是具有挑战性的。这一挑战的出现是因为长聚合物链相互渗透，因此任何给定的分子都可以直接或通过溶剂流动与许多其他分子相互作用。这项拟议的研究将使用新的计算算法来理解聚合物运动、分子水平流体动力学和应用流动之间的联系。这一理解将作为聚合物溶液加工中分子控制的基础，通过展示如何使用浓度和强大的流动来调整分子结构和相应的材料性能。该项目还将通过对学生的跨学科培训和指导，培养下一代科学家。此外，该项目还将开发推广活动，将交互式实验/计算机模拟纳入实践活动，旨在促进未被充分代表的学生参与STEM领域。系统，其中单个线圈显著重叠。半稀溶液具有显著的溶剂介导型流体动力相互作用(HI)和拓扑挂钩。目前的理论能够捕捉平衡性质(松弛时间、分子结构)，但还没有扩展到流动溶液。一种新的构象平均程序能够有效地模拟大系统，从而能够探索HI和链拓扑如何影响流动中高度不平衡的聚合物构象。这项建议将解决两个目标：(I)了解浓度和流体动力相互作用如何影响流动的半稀聚合物溶液中的链动力学；(Ii)捕捉非线性聚合物结构和剪切流如何导致分子挂钩？第一个目标将描述强流对水动力筛选的扭曲，并将平衡标度概念扩展到非平衡系统。第二个目标将使用拓扑不变量来表征挂钩相互作用，以及它们如何影响分子构象的分布。因此，拟议的工作将为从流动涂层到喷墨或3D打印的聚合物的流动控制溶液处理提供重要的见解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Polymers are large, chain-like molecules that are the building blocks of both industrially-relevant products (i.e. plastics, coatings, and fibers) and state-of-the-art advanced materials for devices such as flexible photovoltaics and displays. For many of these applications, the polymer must be processed with an eye towards its final properties; for example, in order to create strong fibers, a "drawing" process is used to align polymer chains. Similarly, coating flows can control molecular packing (and thus charge transport) in semiconducting polymers. For both situations, polymers are manipulated in a liquid solution by applying strong flows. However, it remains challenging to understand how exactly flow influences molecular motions. This challenge arises because long polymer chains interpenetrate, so that any given molecule interacts with many others both directly and via solvent flows. The proposed research will use new computational algorithms to understand the connection between polymer motions, molecular-level fluid dynamics, and applied flows. This understanding will serve as the foundation for molecular control in polymer solution processing, by showing how concentration and strong flows can be used to tune molecular structure and correspondingly material properties. This project will also serve to train the next generation of scientists, through the interdisciplinary training and mentorship of students. In addition, this project will involve the development of outreach events that incorporate interactive experimental/computer simulation into hands-on activities designed to promote the participation of underrepresented students in STEM fields.Polymer solutions are typically processed in the ?semi-dilute? regime, where individual coils overlap significantly. Semidilute solutions are characterized by significant solvent-mediated hydrodynamic interactions (HI) and topological ?hooking?. Current theory is capable of capturing equilibrium properties (relaxation time, molecular structure) but has not been extended to flowing solutions. A new conformational-averaging procedure is capable of efficiently simulating large systems, enabling exploration of how HI and chain topology affect highly out-of-equilibrium polymer conformations in flow. This proposal will address two aims: (i) Understand how concentration and hydrodynamic interactions affect chain dynamics in flowing semi-dilute polymer solutions and (ii) capture how non-linear polymer architectures and shear flows lead to molecular ?hooking?. The first aim will characterize the distortion of hydrodynamic screening by strong flows and extend equilibrium scaling concepts to out-of-equilibrium systems. The second aim will use topological invariants to characterize hooking interactions, and how they affect the distributions of molecular conformations. The proposed work will thus provide insight important for flow-controlled solution processing of polymers, ranging from flow coating to inkjet or 3D printing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.