Studies of Entangled Polymers Under Strong Flow Conditions

该项目旨在了解聚合物溶液在超过线性粘弹性极限的强流动中的行为，以及聚合物充分缠结的浓度和分子量，预计基于蠕动的理论是适用的。 该项目是基于使用瞬态剪切和其他均匀的流动，从近剪切到平面拉伸流，在聚合物链的构象远离平衡状态的条件下。 这包括在足够高的剪切速率下可能存在显著的链拉伸的情况。 这类问题是令人感兴趣的，因为它为检验理论模型的预测提供了基础，也因为对流动和聚合物构型之间关系的理解是加工系统设计中的一个重要组成部分，可以导致宏观材料性能的优化。 提出的研究主要是实验性质的，是基于使用的novl流动池，再加上瞬态光学测量系统。 这些包括双色和相位调制双折射，以及动态光散射和Piv。 这种实验工具的组合提供了缠结点之间的聚合物链段的瞬态配置的数据，以及一个完整的流动表征。 标准流变测试（主要是线性粘弹性）也用于表征流体。 所研究的流体是具有双峰分子量分布的溶液和星星聚合物的溶液。 这两项研究代表了考虑多分散性和聚合物支化的第一步。 最后，最近扩展的基本Doi-Edwards理论将进行评估，并在可能的改进，包括特别是最近的建议，纳入对流约束释放（CCR）。 %%% 本研究的目的是实现基本的理解，这是必要的设计和开发的加工策略，用于生产精密聚合物零件的结构和其他应用，并优化材料性能的分子结构在加工过程中的操纵。 控制设计和优化聚合物加工的能力对于开发具有高于原材料成本的高附加值产品至关重要。

This project is aimed at understanding the behavior of polymeric solutions in strong flows beyond the linear viscoelastic limit, and for concentrations and molecular weights at which the polymers are sufficiently entangled that reptation-based theories are expected to be applicable. The project is based upon the use of transient shear and other homogeneous flows ranging from near-shear to a planar extensional flow, under conditions in which the conformation of polymer chains is far from the equilibrium state. This includes cases at sufficiently high shear rates that there can be significant chain stretch. This general class of problems is intresting because it provides a basis for testing the predictions of theoretical models, and also because an understanding of the relationship between flow and polymer configuration is an essential component in the dsign of processing systems that can lead to optimization of marcroscopic materal properties. The research proposed is dominantly experimental in nature, and is based on the use of novl flow cells that are coupled with transient optical measurement systems. These include both two-color and phase-modulated birefringence, as well as dynamic light scattering and Piv. This combination of experimental tools provides data on the transient configuration of polymer segments between entanglement points, as well as a complete characterization of the flow. Standard rheological tests (primarily linear viscoelasticity) are also used to characterize the fluids. The fluids to be studied are solutions with a bimodal moleclar weight distribution, and solutions of star polymers. These two studies represent a first step toward the consideration of polydispersity and polymer branching. Finally, recent extensions of the basic Doi-Edwards theory will be evaluated, and where possile improved, including particularly recent proposals for the incorporation of convective constraint release(CCR). %%% This research is aimed at achieving the fundamental understanding that is necessary for the design and development of processing strategies for the production of precision polymeric parts for structural and other applications, and for optimizatiton of the material properties by manipulation of molecular structure during processing. The ability to control design and optimize polymer processing is essential to the development of products with a high added value above the raw materials costs.