Configuration and Dynamics in Large Polymer Systems

[00:9832 . 21]新型的催化剂允许以以前不可能的方式剪裁已知聚合物的原子细节结构。所得聚合物的性质往往受到这些变化的强烈影响。这些性质在距离尺度上起源于零点几纳米的量级，因为正是在这个距离尺度上，原子的详细结构才被定义。然而，由这些聚合物生产的大块材料的重要物理性质源于长链分子的混合和组织，这是一个影响更长的距离尺度的问题。为了连接这两个距离尺度，需要新的桥接方法。新的层次结构将用于理解这些原子上的细节变化如何影响单个聚合物的性能，如“弹性聚丙烯”所示，以及混合两种化学性质相似的聚合物得到的混合物。聚合物在纠缠跃迁时的动力学变化将以一种独特的利用模拟家族的分层性质的方式进行研究。这种层次结构允许使用粗粒度模型研究纠缠系统的有趣但相对缓慢的动力学，该模型可以明确地与原子详细结构相关。因此，用与模拟对象完全相同的系统进行实验室实验成为可能。使用脉冲梯度核磁共振的实验和模拟将使用完全相同的双分散聚乙烯熔体。与实验的明确联系将为模拟的发展提供非常强的约束，这将涵盖系统从“非纠缠”行为转变为“纠缠”行为的过渡区域。对模拟的分析可以更好地理解在这个过渡区域中运动聚合物类型的变化。致密聚合物的重要性质所涵盖的广泛的时间和距离尺度，在历史上产生了这些材料的两种不同的、互不关联的模型。用原子细部结构表示的模型受限于短距离和时间尺度。远距离和时间尺度上的现象用粗粒度模型来描述，或者在非常大的尺度上用连续统模型来描述。该项目将产生一个层次模型，在原子细节结构和一系列越来越粗粒度的结构之间架起桥梁，这些结构延伸到纳米尺度，在纳米尺度上，人们可以看到从分子行为到连续行为的转变。

0098321MatticeNew types of catalysts permit the tailoring of the atomisticially detailed structure of known polymers in ways that were not previously possible. The properties of the resulting polymers are often strongly affected by these changes. The properties have their origin at distance scales on the order of a few tenths of a nm, because it is on this distance scale that the atomistically detailed structure is defined. However, the import physical properties of bulk materials produced from these polymers arise from the mixing and organization of long chain molecules, an issue that affects much longer distance scales. The new bridging methods are required in order to connect these two distance scales. The new hierarchy will be employed to understand how these atomistically detailed changes can affect the properties of a single polymer, as illustrated by "elastomeric polypropylene", and the blends obtained upon mixing two chemically similar polymers. The change in the dynamics of polymers at the entanglement transition will be studied in a way that uniquely takes advantage of the hierarchical nature of the family of simulations. This hierarchy permits study of the interesting, but relatively slow, dynamics of the entangled system using a coarse-grained model that can unambiguously be related to an atomistically detailed structure. Therefore it becomes possible to perform laboratory experiments with precisely the same system that is the subject of the simulation. The experiments, using pulsed gradient NMR, and simulations will employ precisely the same bidisperse polyethylene melts. The unambiguous connection with experiment will provide a very strong constraint on the development of the simulation, which will cover the transition region in which the system changes from "unentangled" to "entangled" behavior. Analysis of the simulations should produce a better understanding of the changes in the types of motion polymers in this transition region.The broad range of time and distance scales covered by important properties of dense polymers has historically produced two different, and disconnected, models for these materials. Models expressed with atomistically detailed structures are limited to short distance and time scales. Phenomena at long distance and time scales are described using coarse grained models, or, for very large scales, continuum models. The project will produce a hierarchy of models that bridges between the atomistically detailed structures and a series of increasingly more coarsely grained structures that extend well into the nanoscale regime, where one sees the transition from molecular to continuum behavior.