Relaxation Dynamics of Multiarm Polymer Liquids

长期以来，对明确定义的支链聚合物液体的应力松弛动力学的实验研究被认为对理解商业长链支链聚烯烃的结构-加工关系具有重要意义。当使用表征良好的纠缠支链聚合物进行这些研究时，它们可以直接洞察分子结构、弛豫动力学和流变性之间更一般的关系。拟议研究的目的有三个方面。首先，确定支点运动和约束释放对模型支化聚合物线性流变性的影响。第二，促进对纠缠支化聚合物液体在剪切和拉伸流动中的非线性流变学的基本认识。最后，设计支化聚合物液体中运动和应力松弛过程的可视化方法。提议的研究的好处超出了它对支链聚合物动力学的科学理解的直接影响。例如，当茂金属催化剂化学的进步使得对商业支链聚合物分子结构的空前控制成为可能时，这项研究解决了一个具有相当工业重要性的问题。对这些材料的结构-加工关系的基本理解将有助于减少昂贵的试错实验，现在需要优化新材料的现有工艺。提出这项研究的同时，教科书上也开始出现关于聚合物加工和性能的结构效应的第一次严格处理。这项研究将以多种方式影响教育。通过研究开发的知识将提高教科书和课堂教学中分支聚合物物理信息的质量和范围。所提出的荧光显微镜实验也将为现代高分子科学课程提供一个很好的演示工具。最后，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.