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

就像蜘蛛和蚕通过将聚合物溶液纺成长丝来制造材料一样，人类将这些材料纺成纤维，用于纺织品，过滤器和许多其他应用。当这些材料被拉成纤维、被压入瓶中，或者当消费者将洗发剂和肥皂涂在头发或身体上时，同样的流动，即“拉伸流动”，与剪切流动结合发生。因此，表面活性剂的长聚合物和长线状聚集体（即，“胶束”）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。这是由于在实验室中控制这些材料的拉伸流动以及模拟其流体机械和分子行为的复杂相互作用的困难。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”）、一种解释聚合物或胶束的缠结的方法（“滑动链接模拟”）以及对长丝的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，并且材料可以更好地设计用于其预期应用。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如何导致囊性纤维化疾病严重程度的例子向K-12学生进行说明。 在我们的小组开发的“滑簧”和“指针”模拟方法将被用来模拟拉伸流动的聚合物溶液和线状胶束溶液中测量的“毛细管破裂”（CaBER）和“滴在基板上”（DoS）流变仪。这些流变仪通常用于移动的聚合物和表面活性剂溶液的拉伸测量。建模将结合联合收割机适当的描述，在这些测量与先进的模拟聚合物和胶束的合奏。这将有助于从这些流体的复杂流变学中解开这些设备中的非理想流动运动学的混淆效应所产生的不确定性，从而在理解和更准确的建模和材料设计方面取得突破。动机和方法将告知夏季外展计划，在密歇根大学和底特律地区的学校，使用动手聚合材料在延伸流K-12学生。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.