NMR Investigation of Segmental Dynamics in Multicomponent Systems

在多组分体系中，聚合物的分子运动可能受到其他合成聚合物、固体底物、填料或生物结构的强烈影响。这种动力学变化显著地影响着输运和力学性能。这项研究的长期目标是了解如何预测混合过程中聚合物动力学的变化。多组分聚合物体系表现出复杂的动力学特性。通过充分描述若干模型混合物的动力学特性，可以取得重大进展。该研究将描述：1)模型单相共混物（低分子量聚苯乙烯/聚异戊二烯）中两组分的段动力学；2)模型单相共混中两组分的长度和时间尺度运动更长；3)以聚异戊二烯为次要组分的几种单相共混物的无限稀释极限段动力学；模型纳米复合材料（C60/聚丁二烯）的结构与动力学。此外，将讨论共混动力学的两个关键概念方面：1)混相共混物（聚异戊二烯/聚乙烯）中局部迁移率和局部结构之间的相关性；2)决定局部流动性的区域的大小。表征复杂混合物中的动力学需要协调应用许多不同的实验技术。该研究主要依赖于多场核磁共振弛豫时间测量和固体核磁共振测量的节段和正常模式运动，以及中子散射来评估纳米级复合材料中的聚集。这条研究路线将导致对混相聚合物混合物的复杂特征和有用性质的理解，并最终能够预测这些性质。从模型纳米复合材料的研究中获得的见解可能导致预测与聚合物接触的纳米器件附近离子和小分子的传输特性的能力。动力学实验和分子动力学计算机模拟之间的比较将导致力场的改进和在材料科学及其他领域进行更精确模拟的能力

In multicomponent systems, the molecular motion of a polymer may be strongly affected by the presence of other synthetic polymers, solid substrates, fillers, or biological structures. Such changes in dynamics significantly influence transport and mechanical properties. The long term goal of this research is to understand how to predict the changes in polymer dynamics which occur with mixing. Multicomponent polymer systems exhibit complex dynamics. Significant progress can be made by fully characterizing the dynamics of a number of model mixtures. The proposed research will characterize: 1) segmental dynamics of both components in a model one-phase blend (low molecular weight polystyrene/polyisoprene); 2) longer length and time scale motions of both components in a model one-phase blend; 3) segmental dynamics in the limit of infinite dilution for several one-phase blends with polyisoprene as the minor component; 4) structure and dynamics of a model nano-composite (C60/polybutadiene). In addition, two key conceptual aspects of blend dynamics will addressed: 1) the correlation between local mobility and local structure in a miscible blend (polyisoprene/polyvinylethylene); 2) the size of the regions which determine local mobility. Characterizing dynamics in complex mixtures requires the coordinated application of a number of different experimental techniques. The proposed research primarily relies upon multiple field NMR relaxation time measurements and solid-state NMR measurements of segmental and normal model motion, and neutron scattering to assess aggregation in a nanoscale composite.%%%This line of research should lead to an understanding of the complex features and useful properties of miscible polymer blends, and ultimately the ability to predict these properties. Insights from the study of a model nano-composite could lead to the ability to predict transport properties of ions and small molecules near nano-devices in contact with polymers. Comparisons between dynamics experiments and molecular dynamics computer simulations will lead to improved forcefields and the ability to perform more accurate simulation in materials science and beyond