Scattering Studies of Polymer Deformation in Flowing Solutions

当聚合物流体流动时，单个聚合物链可能因流体动力而变形。了解这种变形过程是聚合物流变学的中心研究目标，因为单个链的构象动力学最终会产生非牛顿流动特性。尽管具有明显的重要性，但很少有人尝试直接研究流动中的聚合物链动力学。在这个项目中，低角度光散射被用于探测聚合物在稳定的单轴拉伸流稀释溶液中的拉伸和取向。先前资助期的结果表明，在相对射流之间产生的模型流中的链拉伸水平可能不像以前通过间接光学方法（双折射）或当前分子理论所建议的那样大。控制柔性聚合物变形速率和最终变形水平的物理机制目前正在通过改变分子量、溶剂类型和质量、伸长率和骨架刚度来进行研究。实验是在最近完成的光散射装置中进行的，该装置能够对位于停滞点的极小散射体积进行低角度测量。这些测量将通过双折射研究和更多瞬态应力环境下的流动实验来补充。本研究旨在了解流动中的大分子行为，这在纤维纺丝、湍流减阻和提高采收率等技术领域具有重要的基础科学和技术意义。

When polymeric fluids flow, individual polymer chains may become deformed by hydrodynamic forces. Understanding this deformation process is a central research goal of polymer rheology, as the conformational dynamics of individual chains ultimately create non-Newtonian flow properties. Despite this obvious importance, few attempts have been made to study directly polymer chain dynamics in flow. In this project, low-angle light scattering is used to probe the stretching and orientation of polymers in steady uniaxial elongational flow of dilute solutions. Results from the previous funding period indicate that the level of chain stretching in a model flow, created between opposed jets, may not be as great as previously suggested by indirect optical methods (birefringence) or current molecular theories. The physical mechanisms responsible for controlling the rate of deformation and the ultimate deformation level of flexible polymers are now being examined by varying molecular weight, solvent type and quality, elongation rate, and backbone stiffness. Experiments are being conducted in a recently completed light-scattering apparatus capable of low-angle measurements off an extremely small scattering volume located at a stagnation point. These measurements will be complemented by birefringence studies and flow experiments in more transient stress environments. This research aims to understand macromolecular behavior in flow, which is of fundamental scientific importance as well as in technology, such as fiber spinning, turbulent-drag reduction, and enhanced oil recovery.