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

就像蜘蛛和蚕虫通过将聚合物溶液纺成长线来制造材料一样，人类将这种材料纺成长丝，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，被迫进入瓶子，或者当消费者将洗发水和肥皂涂抹在头发或身体上时，同样的流动，也就是“拉伸流动”，与剪切流动一起发生。因此，表面活性剂的长聚合物和长线状聚集体(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。这是因为很难在实验室控制这些材料的拉伸流动，也很难对它们的流体力学和分子行为的复杂相互作用进行建模。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”)、解释聚合物或胶束纠缠的方法(“滑链模拟”)和对细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。其结果将是可以更好地预测这些材料的拉伸流动，并且可以更好地设计这些材料以满足其预期的应用。这一区域的重要性将通过一个例子向K-12学生说明，即无法清除肺部粘性聚合物粘液是囊性纤维化疾病严重程度的原因。我们小组开发的“滑动弹簧”和“指针”模拟方法将用于模拟在“毛细管破裂”(CABER)和“落基”(DOS)流变仪中测量的聚合物溶液和线状胶束溶液的拉伸流动。这些流变仪是用于流动聚合物和表面活性剂溶液的拉伸测量的常用流变仪。该模型将结合对这些测量中的流动运动学的适当描述与对聚合物和胶束整体的高级模拟。这将有助于将这些设备中非理想流动运动学的混杂效应造成的不确定性与这些流体的复杂流变性分开，从而在材料的理解和更准确的建模和设计方面取得突破。这些动机和方法将为密歇根大学和底特律地区学校的K-12学生暑期外展项目提供参考，该项目在延伸流程中使用亲身实践的聚合物材料。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。

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.