Directed Crystallization Precursor Structures in Polymer Melt by Flow

这项拟议的研究旨在研究聚合物中流动诱导结晶的几个基本问题，重点是在相变的早期阶段发生的事件。这些问题包括：(1)在充分结晶之前通过流动在过冷聚合物熔体中形成由微纤丝(SHISH)和跨晶片(KEBBS)组成的纳米支架的途径；(2)内部材料参数(链长、长度分布和链分支，或松弛时间谱)与外部流动参数(温度、应变和应变率或应力)和初始前体结构的形成之间的关系；(3)SHISH和KEBA微结构中流动诱导结晶前驱体结构的性质。拟议的研究计划将包括：(I)使用聚合物与模型化合物的混合物来研究流动诱导的前体结构，(Ii)使用包括流变学、原位拉曼光谱、同步辐射SAXS/WAXD技术和非原位显微方法在内的组合方法，以及(Iii)弱剪切流动和强拉伸流动研究的结果的比较。流动诱导结晶问题仍然是当今聚合物加工中最重要的问题之一，它仍然没有被完全理解。过去的主要障碍主要是由于缺乏合适的原位表征工具来确定流动诱导结晶的最早阶段的结构。使用最近可用的同步加速器X射线技术，这些障碍已经有效地克服了。在拟议的研究中获得的深入了解将提高聚合物工业将结晶聚合物的结构、形态、工艺和性能关系联系起来的能力。这一提议的更广泛影响有几个。直接的好处是，拟议的活动将在两个科学机构(石溪大学和国家同步加速器光源)之间建立紧密的联系。学生和科学家将在这两个机构接受培训。他们将接触到相关的工业问题，并将有机会通过工业科学家的直接互动来解决这些问题。他们还将参与石溪MRSEC暑期教育项目，在该项目中，他们将指导本科生和工业科学家进行简单的同步辐射X射线实验。

The proposed research aims to investigate several fundamental issues of flow-induced crystallization in polymers with an emphasis on events that occurred at the earliest stages of phase transition. These issues include: (1) the pathway to forming nanostructured scaffolds comprised of microfibrils (shish) and trans-crystalline lamellae (kebabs) in undercooled polymer melt by flow prior to full scale crystallization; (2) the relationships among the internal material parameters (chain length, length distribution and chain branching, or the relaxation time spectrum), the external flow parameters (temperature, strain and strain rate, or stress), and the formation of the initial precursor structures; and (3) the nature of the flow-induced crystallization precursor structures in shish and kebab microstructures. The proposed research plan will include: (i) the use of polymer blends with model compounds to enable the investigation of the flow-induced precursor structures, (ii) the use of combined methods including rheology, in-situ Raman spectroscopy and synchrotron SAXS/WAXD techniques and ex-situ microscopic methods, and (iii) the comparison of results from weak shear-flow and strong elongation-flow studies.The scientific merits of the proposed study are as follows. The subject of flow-induced crystallization remains to be one of the most important problems in polymer processing today, and it is still not yet fully understood. The major hurdles in the past were mainly due to the lack of suitable in-situ characterization tools to determine the structures at the earliest stages of flow-induced crystallization. Using the recently available synchrotron X-ray techniques, these hurdles have been effectively overcome. The in-depth understanding obtained in the proposed study shall increase the ability of the polymer industry to correlate the structure, morphology, process and property relationships for crystalline polymers. The broader impacts of this proposal are several. The immediate benefit is that the proposed activities will produce tight links between two scientific institutions (Stony Brook University and the National Synchrotron Light Source). Students and scientists will be trained in both institutions. They will be exposed to relevant industrial problems and will have a chance to tackle these problems with direct interactions from industrial scientists. They will also be involved in the Stony Brook MRSEC summer education program, where they will supervise undergraduate students and industrial scientists to carry out simple synchrotron X-ray experiments.