Relaxations and Molecular Motions in Polymers

聚合物中的弛豫和分子运动

• 批准号: 9972225
• 负责人: Richard Boyd
• 金额: $ 30万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-06-01 至 2003-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9972225&HistoricalAwards=false
• 关键词: Relaxations; Molecular; Motions; Polymers

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.

9972225 boyd目前的研究涉及平行或伴随方法来阐明松弛机制。第一种方法涉及对精心选择的系统进行仔细的实验表征，第二种方法涉及分子运动的原子级模拟。介质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进行测量。分子动力学（MD）模拟可以生成原子在时间轨迹上的位置，用于研究与实验研究相同系统中的分子运动。需要解决的具体问题如下。芳香族聚酯聚对苯二甲酸乙二醇酯（PET）在玻璃化转变下有明显的松弛。其背后的分子运动尚不清楚。它的近亲聚萘乙烯酸酯（PEN）有两个这样的过程，因此更不为人所知。对这两种聚合物及其共聚物的玻璃下工艺和玻璃过渡区进行彻底的介电表征。特别要注意的是高频、短时间区域，在那里可以与相同系统上的MD模拟进行直接比较。另一个要研究的体系是直线型脂肪族聚酯共聚物。在玻璃下过程和玻璃过渡区域，可以与MD模拟在同一系统上进行直接比较。另一个要研究的体系是直线型脂肪族聚酯共聚物。将研究玻璃下过程和玻璃过渡区域。同伴MD模拟将被制作。液晶全芳烃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如何联系的更详细的理解将会发展。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的积极平衡作出贡献的部门之一。它的主干是聚合物的制造和加工。这些材料已经融入到日常生活的方方面面。它们的行为，以及因此对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。后者是明确定义的温度和时间区域，在这些区域上，性质通常会发生显著变化。这些过程的存在是由于各种类型的分子运动随着温度的升高而开始的。为了合理地为新应用定制现有材料并设计新材料，在最基本的层面上理解松弛是很重要的。这需要理解潜在的分子运动。实现这种洞察力是聚合物科学的一个重要目标。