Modelling extensional flow properties of solutions of polymers and thread-like micelles

就像蜘蛛和蚕把聚合物溶液纺成长长的线来制造材料一样，人类把这些材料纺成细丝，用于纺织品、过滤器和许多其他用途。同样的流动，即“拉伸流”，当这些材料被拉入纤维，强行进入瓶子，或者当消费者将洗发水和肥皂涂抹在头发或身体上时，会与剪切流结合发生。因此，长聚合物和表面活性剂的长线状聚集体（即“胶束”）在拉伸流动中的行为是许多产品设计的基础。然而，人们对它们在溶液中的行为仍然知之甚少。这是因为在实验室中很难控制这些材料的拉伸流动，也很难模拟它们的流体力学和分子行为之间复杂的相互作用。因此，将使用一种新的分析方法，该方法结合了分子模拟技术（“布朗动力学”），一种计算聚合物或胶束缠结的方法（“滑移模拟”）以及对细丝流体力学的适当处理。这种结合最终将使实验数据得到正确的解释。结果将是，这些材料的拉伸流动可以更好地预测，材料可以更好地设计为其预期的应用。该区域的重要性将通过无法从肺部清除粘性聚合物粘液是囊性纤维化疾病严重程度的原因的例子向K-12学生说明。我们小组开发的“滑簧”和“指针”模拟方法将用于模拟聚合物溶液和线状胶束溶液的拉伸流动，这些溶液在“毛细管破裂”（CaBER）和“滴在基体上”（DoS）流变仪中测量。这些流变仪通常用于可移动聚合物和表面活性剂溶液的拉伸测量。建模将结合这些测量中流动运动学的适当描述与聚合物和胶束的高级模拟。这将有助于解开这些设备中非理想流动运动学与这些流体的复杂流变性的混淆效应所带来的不确定性，从而在理解和更准确的材料建模和设计方面取得突破。其动机和方法将为密歇根大学（University of Michigan）和底特律地区学校的K-12学生暑期推广项目提供信息，该项目将在延伸流中使用亲身实践的聚合物材料。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Just as spiders and silkworms make materials by spinning solutions of polymer into long threads, humans spin such materials into filaments for textiles, filters, and many other applications. The same kind of flow, namely “extensional flow,” occurs in combination with shear flow when such materials are drawn into fibers, forced into bottles, or when consumers apply shampoos and soaps to their hair or bodies. Thus, the behavior of long polymers and long thread-like aggregates of surfactant (i.e., “micelles”) in extensional flow is basic to the design of many products. Yet their behavior in solution is still poorly understood. This is due to the difficulty of controlling extensional flows of these materials in the lab, and of modelling the complex interactions of their fluid mechanical and molecular behavior. Therefore, a new method of analysis will be used that combines a molecular simulation technique (“Brownian dynamics”), a method of accounting for the entanglements of the polymers or micelles (“slip-link simulations”) and proper treatment of the fluid mechanics of filaments. This combination will finally allow experimental data to be interpreted properly. The result will be that extensional flows of these materials can be better predicted, and the materials can be better designed for their intended applications. The importance of the area will be illustrated to K-12 students through the example of how an inability to clear sticky polymeric mucus from lungs is responsible for the severity of disease in cystic fibrosis. The “slip-spring” and “pointer” simulation methods developed in our group will be used to model extensional flow of polymeric solutions and threadlike micellar solutions measured in “capillary break-up” (CaBER) and “drop-on-substrate” (DoS) rheometers. These rheometers are the common ones used for extensional measurements of mobile polymer and surfactant solutions. The modeling will combine proper description of the flow kinematics in these measurements with advanced simulations of ensembles of polymers and micelles. This will help disentangle uncertainties created by the confounding effects of the non-ideal flow kinematics in these devices from the complex rheology of these fluids, leading to a breakthrough in understanding and more accurate modelling and design of materials. The motivations and methods will inform a summer outreach program to K-12 students at the University of Michigan and in Detroit-area schools, using hands-on polymeric materials in extensional flows.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.