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，以及聚合物充分纠缠的浓度和分子量，期望基于重复的理论适用。该项目基于瞬态剪切和其他均匀流动的使用，范围从近剪切到平面拉伸流动，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，可以有显著的链拉伸的情况。这类问题很有趣，因为它为测试理论模型的预测提供了基础，也因为理解流动和聚合物构型之间的关系是设计加工系统的重要组成部分，可以优化宏观材料性能。提出的研究主要是实验性的，并且基于使用与瞬态光学测量系统相结合的新型流动细胞。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纠缠点之间聚合物段的瞬态结构数据，以及对流动的完整描述。标准流变试验（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形聚合物的溶液。这两项研究是研究多分散性和聚合物分支的第一步。最后，将评估最近对基本的Doi-Edwards理论的扩展，并在可能的情况下进行改进，包括最近提出的结合对流约束释放（CCR）的建议。这项研究的目的是实现对设计和开发用于结构和其他应用的精密聚合物部件生产的加工策略所必需的基本理解。并在加工过程中通过操纵分子结构来优化材料性能。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.