Subglass Relaxation Processes in Polymers

非晶聚合物玻璃下弛豫的分子机制的细节在很大程度上仍然是一个谜。虽然有大量有用的实验描述，但这些实验很少具体地揭示发生的运动的性质。分子建模或模拟在解释分子运动的细节方面正变得越来越有价值。最近一项重要的进展是能够通过分子动力学（MD）模拟生成非晶聚合物熔体和玻璃中的结构和堆积的详细描述。在目前的工作中，这种建模的进展将被用于描述玻璃下弛豫。这项工作将与介电弛豫实验一起进行。待研究的体系包括：主链液晶芳族聚酯的玻璃下工艺；其它芳香族聚酯的玻璃下工艺；聚乙烯中的γ弛豫；由于内部旋转势垒低，在设计上处于极低温度的玻璃下层工艺；还有侧链介介液晶聚合物。不像许多其他材料，如金属和陶瓷，所有聚合物材料的有用性取决于它们在分子尺度上非常动态的事实。也就是说，组成分子处于恒定的运动状态，运动的种类决定了它们的性质。即使在表面上坚硬如玻璃的聚合物中，残余的分子运动也决定了强度和韧性等行为。然而，对这些运动还没有一个清晰的认识。目前的工作旨在实现这一认识，以便开发更好的材料。现代计算机建模技术将与复杂的实验工具相结合，以实现这一目标。

The details of the molecular mechanisms underlying subglass relaxations in amorphous polymers remain largely a mystery. Although there is a considerable body of useful experimental description, the experiments are rarely specific in revealing the nature of the motions taking place. Molecular modelling or simulation is becoming of increasing value in interpreting the details of molecular motion. An important recent advance has the been the ability to generate, via molecular dynamics (MD) simulation, detailed description of the structure and packing in amorphous polymeric melts and glasses. In the present work, such advances in modelling will be exploited in describing subglass relaxations. The work will be done in association with dielectric relaxation experiments. Systems to be studied include subglass processes in main-chain liquid crystalline aromatic polyesters; subglass processes in other aromatic polyesters; the gramma- relaxation in polyethylene; subglass processes that are, by design, at very low temperature by virtue of low internal rotational barriers; and, side-chain mesogen liquid crystalline polymers. Unlike many other materials, such as metals and ceramics, the usefulness of all polymeric materials depends on the fact that they are very dynamic on the molecular scale. That is, the constituent molecules are in a constant state of motion and the kinds of motion determine the properties. Even in polymers that are apparently rigid and glass-like, residual molecular motions determine such behavior as strength and toughness. However there is not yet a clear understanding of these motions. The present work is directed toward attaining this understanding in order that better materials can be developed. Modern computer modelling techniques will be combined with sophisticated experimental tools in accomplishing this goal.