UNS: The Effect of Flow-Induced Concentration Inhomogeneities on the Flow of Polymer Solutions

1510333（Leal）已经发现，在复杂流体如聚合物和表面活性剂溶液、液晶等的处理过程中，溶液中的大分子可以迁移到更集中的区域。拟议研究的目标是了解这种现象，即聚合物的剪切诱导条带。发现这一现象的根本原因对石化、消费品和食品工业中常见的复杂流体的加工和制造具有重要的技术意义。 当大分子悬浮液（例如，表面活性剂、聚合物和可能的蛋白质）被剪切时，存在所谓的应力诱导的大分子或胶束向溶液的较高浓度区域的迁移，通过所谓的Helfand Fredrickson（HF）机制。在这项工作中，co-PI建议探索这种机制是否可以在聚合物溶液中产生宏观浓度梯度-这种现象有些争议。 的co-PI，通过先前的理论工作，已经表明，在缠结的解决方案中的聚合物应力和浓度之间的耦合产生简单的剪切流的线性不稳定性，这种不稳定性导致剪切带。 在该提案中，他们提出了一种协调的实验和计算方法来研究这个问题，然后将结果推广到其他流动：（a）显示“喷射”不稳定性的管中的压力驱动流动，以及（B）2辊和4辊研磨流动中的流动，即，在不同的应力模式甚至拉伸流动下测试他们的模型。所提出的方法将涉及仔细的实验（使用流变核磁共振和中子散射）和计算。计划进行研究的推广和传播，让研究生参与研究。此外，还将向业界公布结果。

1510333(Leal)It has been found that during the processing of complex fluids, such as polymer and surfactant solutions, liquid crystals, etc., large molecules in the solution can migrate to more concentrated areas. The goal of the proposed research is to understand this phenomenon, known as shear-induced banding, for the case of polymers. Discovering the fundamental reasons for this phenomenon has significant technological implications in processing and manufacturing of complex fluids that are common in the petrochemical, consumer products and the food industry. When a macromolecular suspension (e.g., surfactants, polymers, and possibly proteins) is sheared, there is what is known as stress-induced migration of the macromolecules or micelles toward regions of higher concentration of the solution, via the so-called Helfand Fredrickson (HF) mechanism. In this work, the co-PIs propose to explore whether this mechanism can produce macroscopic concentration gradients in polymer solutions - a case where this phenomenon is somewhat controversial. The co-PIs, through prior theoretical work, have suggested that the coupling between the polymer stress and concentration in entangled solutions produces a linear instability for simple shear flow, and this instability leads to shear banding. In this proposal, they propose a coordinated experimental and computational approach to investigate this problem, and then to generalize the results to other flows: (a) pressure driven flow in a tube which exhibits a "spurt" instability, and (b) flow in 2- and 4-roll milling flows, i.e., testing their models under different stress patterns and even extensional flows. The proposed approach will involve both careful experiments (using rheo-NMR and neutron scattering) and computations. Outreach and dissemination of research is planned, involving graduate students in research. In addition, results will be disseminated to the industry.