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

1510333(Leal)人们发现，在聚合物和表面活性剂溶液、液晶等复杂流体的处理过程中，溶液中的大分子可以迁移到更集中的区域。这项拟议研究的目标是理解这种现象，即聚合物的剪切诱导带状现象。发现这一现象的根本原因对加工和制造复杂流体具有重要的技术意义，这些复杂流体在石化、消费品和食品工业中很常见。当大分子悬浮液(如表面活性剂、聚合物，可能还有蛋白质)被剪切时，大分子或胶束会通过所谓的Helfand Fredrickson(HF)机制，在应力诱导下向溶液浓度较高的区域迁移。在这项工作中，共同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-这一现象在某种程度上是有争议的。通过先前的理论工作，共同PI已经表明，对于简单剪切流动，聚合物应力和纠缠溶液中的浓度之间的耦合产生线性不稳定性，并且这种不稳定性导致剪切带。在这个建议中，他们提出了一种实验和计算相结合的方法来研究这个问题，然后将结果推广到其他流动：(A)压力驱动的管内流动，表现出“喷涌”不稳定性，以及(B)二辊和四辊磨削流中的流动，即在不同应力模式下甚至伸展流动下测试他们的模型。建议的方法将包括仔细的实验(使用Rheo-核磁共振和中子散射)和计算。计划扩大和传播研究，让研究生参与研究。此外，结果将向行业传播。

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.