Relaxation Dynamics of Multiarm Polymer Liquids

长期以来，支化聚合物液体的应力松弛动力学实验研究一直被认为是理解商业长链支化聚烯烃结构-加工关系的重要手段。当使用表征良好的缠绕支化聚合物进行这些研究时，它们可以提供对分子结构、松弛动力学和流变学之间更一般关系的直接洞察。这项拟议研究的目标有三个。首先，确定支化点运动和约束释放对模型支化聚合物线性流变学的影响。第二，加深对支化聚合物液体在剪切和拉伸流动中的非线性流变性的基本认识。最后，设计了支化聚合物液体中运动和应力松弛过程的可视化方法。这项拟议研究的好处超出了它对支化聚合物动力学的科学理解的直接影响。例如，这项研究解决了一个相当重要的工业问题，因为茂金属催化剂化学的进步使商业支化聚合物的分子结构得到了前所未有的控制。对这些材料的结构-加工关系的基本了解将有助于减少目前优化新材料现有工艺所需的昂贵的反复试验。这项拟议的研究也是在第一次严格处理建筑对聚合物加工和性能的影响开始出现在教科书中的时候进行的。这项研究将以多种方式影响教育。通过学习开发的知识将提高课本中和课堂上教授的关于支化聚合物物理的信息的质量和范围。拟议的使用分支DNA的荧光显微镜实验也将为聚合物科学的现代课程提供一个很好的演示工具。最后，将参与该项目的研究生和本科生研究人员将接受聚合物科学和工程几个新兴领域的培训。

Experimental studies of stress relaxation dynamics of well-defined branched polymer liquids have long been recognized as important for understanding structure-processing relationships in commercial long-chain branched polyolefins. When these studies are performed using well-characterized entangled branched polymers they can provide direct insight into more general relationships between molecular architecture, relaxation dynamics, and rheology. The objective of the proposed research is three-fold. First, to determine the effect of branch point motion and constraint release on the linear rheology of model branched polymers. Second, to advance fundamental understanding of nonlinear rheology of entangled branched polymer liquids in shear and extensional flow. Finally, to devise methods for visualizing motion and stress relaxation processes in branched polymer liquids. Benefits of the proposed research extend beyond its direct impact on scientific understanding of branched polymer dynamics. The research, for example, addresses a problem of considerable industrial importance at a time when advances in metallocene catalyst chemistry are allowing unprecedented control of molecular architecture in commercial branched polymers. Fundamental understanding of structure-processing relationships in these materials will help reduce expensive trial-and-error experimentation now required to optimize existing processes for new materials. The proposed research also comes at a time when the first rigorous treatments of architecture effects on polymer processing and properties are beginning to appear in textbooks. This research will impact education in a variety of ways. Knowledge developed by study will improve the quality and scope of information about branched polymer physics written in text books and taught in the classroom. The proposed fluorescence microscopy experiments using branched DNA will also provide an excellent demonstration tool for modern courses in polymer science. Finally, the graduate and undergraduate student researchers who will work on the project will receive training in several emerging areas of polymer science and engineering.