Relaxations and Molecular Motions in Polymers

9972225本研究涉及平行或同伴的方法来阐明松弛机制。 第一个涉及精心选择的系统和第二调用原子水平的分子运动的模拟仔细的实验表征。 介电弛豫光谱是主要的实验工具，因为它允许在一个非常广泛的时间范围内测量。 分子动力学（MD）模拟，它产生原子的位置在一个时间轨迹是用来研究分子运动在同一系统中的实验研究。 需要解决的具体问题涉及以下方面。 芳香族聚酯聚对苯二甲酸乙二酯（PET）在低于其玻璃化转变温度时具有显著的弛豫. 它背后的分子运动尚不清楚。 它的近亲聚萘甲酸乙二醇酯（PEN）有两个这样的过程，因此更不了解。 彻底的介电特性的亚玻璃过程和玻璃化转变区是进行两种聚合物和它们的共聚物。 特别注意的是要给予高频率，短时间的区域，可以直接比较与MD模拟相同的系统。 另一个研究体系是线性脂肪族聚酯共聚物。 亚玻璃过程和玻璃化转变区，其中直接比较与MD模拟相同的系统可以。 另一个研究体系是线性脂肪族聚酯共聚物。 亚玻璃过程和玻璃化转变区都将被研究。 将进行伴随MD模拟。 液晶全芳族聚酯的模拟工作也将继续进行。 在所有这些领域中，对弛豫过程和分子运动之间的联系将有相当详细的了解。美国的化学工业是国家经济的重要组成部分。 它是继续为国际贸易带来积极平衡的部门之一。 其支柱是聚合物的制造和加工。 这些材料已成为交织到日常生活的各个方面。 它们的行为，以及因此对于给定应用的给定材料的选择，敏感地取决于弛豫过程的存在。 后者是定义明确的温度和时间区域，在此区域内，性质通常会发生显着变化。 这些过程的存在是由于随着温度的升高，各种类型的分子运动开始发生。 为了合理地调整现有材料的新应用和设计新的，重要的是要在最基本的水平上理解弛豫。 这需要了解潜在的分子运动。 实现这一认识是聚合物科学的一个重要目标。

9972225BoydThe present research deals with parallel or companion approaches to elucidation of relaxation mechanisms. The first involves careful experimental characterization of well chosen systems and the second invokes atomistic level simulations of molecular motions. Dielectric relaxation spectroscopy is the principal experimental tool to be employed as it allows measurements over an extremely broad temporal range. Molecular dynamics (MD) simulations, which generate atom positions over a time trajectory are to be used to study molecular motions in the same systems as studied experimentally. The specific probems to be addressed concern the following. The aromatic polyester poly(ethylene terephthalate) (PET) has prominent relaxation below it glass transition. The molecular motions underlying it are not understood. Its close relative poly(ethylene naphthylate) (PEN) has two such processes and thus is even less understood. Thorough dielectric characterization of both the subglass processes and the glass transition region is to be carried out on both polymers and their copolymers. Special attention is to be given to the high frequency, short time region where direct comparisons with MD simulations on the same systems can be made. Another system for study will be linear aliphatic polyester copolymers. Both the subglass processes and glass transition region where direct comparisons with MD simulations on the same systems can be made. Another system for study will be linear aliphatic polyester copolymers. Both the subglass processes and glass transition region will be investigated. Companion MD simulations are to be made. Simulation efforts on liquid crystalline wholly aromatic polyesters will be continued as well. In all of these areas a considerably more detailed understanding of how relaxation processes and molecular motions are connected will evolve.The chemical industry of the United States is an important segment of the nation's economy. It is one of the segments that continues to contribute a positive balance in international trade. Its backbone is the manufacture and processing of polymers. These materials have become interwoven into every aspect of everyday life. Their behavior, and hence the choice of a given material for a given application, depends sensitively on the presence of relaxation processes. The latter are well defined regions of temperature and time over which properties change, often dramatically. The presence of the processes is due to the onset of various types of molecular motions with increasing temperature. In order to rationally tailor existing materials for new applications and design new ones, it is important that relaxations be understood at the most fundamental level possible. This requires understanding of the underlying molecular motions. Achieving this insight is an important goal of polymer science.