Structure and Relaxation Processes in Polymers

9630061博伊德这项研究的总体目标是更好地理解松弛过程，特别是在分子水平上。将使用两种方法。一种是利用最近开发的令人印象深刻的能力来进行分子水平的计算机模拟，以在块状、密集堆积的聚合物中进行结构和动态过程的模拟。另一种方法是实验性的，使用介电松弛技术来定位和表征松弛过程。模拟工作的一部分将针对发展对熔体到玻璃转变过程的更好的分子理解。我们最近的研究表明，随着玻璃的形成，动态过程在空间上变得不同。分子动力学(MD)模拟将被用来表征局部结构并将其与链动力学相关联。这将在具有亚玻璃松弛和不具有亚玻璃松弛的聚合物中完成。在更实际的情况下，这些模拟将被用来发展对玻璃化转变温度和化学结构之间的联系的结构-性质的理解。事实上，将继续使用MD模拟从聚合物化学结构式中预测Tg值。介电测量将被用来产生更好的数据，以便与MD结果进行比较。液晶聚合物(LCP)是介于非晶态聚合物和晶态聚合物之间的中间产物。为了更好地理解主链热致液晶中发生的驰豫过程，分子动力学模拟将被应用于主链热致液晶中。另一类LCP涉及介晶单元并入侧链的情况。介电研究将被用来表征侧链介晶液晶的弛豫。聚合物材料构成了现代技术的基石之一。无定形聚合物既可以作为玻璃，也可以作为弹性体，是这些材料的重要组成部分。它们作为材料的行为，包括区分它们的玻璃态或弹性体行为，在很大程度上取决于松弛过程的存在和相关的时间温度位置。相应地，弛豫过程的源头是各种类型的分子运动。***

9630061 Boyd The general goal of this research is to develop a better understanding of relaxation processes, especially at the molecular level. Two approaches are to be used. One takes advantage of the impressive ability developed recently for carrying out molecular level computer simulations of the structure and dynamic processes in bulk, dense-packed polymers. The other approach is experimental and employs the dielectric relaxation technique to locate and characterize relaxation processes. Part of the simulation effort will be directed toward developing a better molecular understanding of the melt to glass transition process. Our recent research showed that as the glass forms the dynamic processes become spatially heterogeneous. Molecular dynamics (MD) simulations are to be used to characterize the local structure and relate it to the chain dynamics. This will be done both in polymers that possess subglass relaxations and those that do not. In a more practical vein, the simulations will be used to develop structure- property understanding of the connection between the glass transition temperature and chemical structure. In fact the use of MD simulations to predict Tg values from the polymer chemical structural formula will be pursued. Dielectric measurements will be used to generate better data for comparison with the MD results. Liquid crystalline polymers (LCPs) are an intermediate case between the broad classes of amorphous and crystalline polymers. MD simulations are to be applied to main-chain thermotropic LCPs in order to better understand the relaxation processes that occur in them. Another class of LCP concerns the case where the mesogenic unit is incorporated in a side-chain. Dielectric studies are to be carried out to characterize the relaxations in side chain mesogenic LCPs. %%% Polymeric materials form one of the cornerstones of modern technology. Amorphous polymers, both as glasses and as elastomers, comprise an important compone nt of these materials. Their behavior as materials, including differentiating between their glassy or elastomeric behavior, is largely determined by the presence and associated time temperature location of relaxation processes. In turn, relaxation processes have their source in molecular motions of various types. ***