Orientation Induced Crystallization in Multi-Component Melts Under Flow

技术综述：本研究旨在研究流动状态下多组分聚合物熔体中新发现的取向诱导结晶前驱体结构现象。这些现象包括(1)纳米尺度和宏观尺度的前体结构的形成，它们可以作为指导结晶过程的多尺度支架；(2)流动诱导的前体结构、流变行为、多组分相行为和流场类型之间的关系。为了解决提出的问题，制定了以下研究计划。首先，选定的全部以聚烯烃为基础的多组分体系将包括模型化合物的聚合物共混物(例如，高分子量可结晶物种和低分子非结晶物种)、链段烯烃嵌段共聚物(只有一个可结晶链段)和具有分散良好的表面改性碳纳米纤维/纳米管的聚烯烃纳米复合材料。其次，为了理解流变行为，动态和瞬时模式下的实验数据将用基于Gex的模型来描述，以产生导致前驱体结构形成的松弛机制。第三，随着结构的实时发展，将使用包括流变学、原位同步辐射小角X射线散射(SAXS)、广角X射线衍射(WAXD)和光散射技术在内的组合方法。最后，为了了解不同流场的影响，将比较简单剪切(含旋转单元)和拉伸流动(不含旋转单元)的结果。非技术综述：流动诱导结晶的问题，特别是在聚合物共混物、嵌段共聚物和纳米复合材料等多组分体系中，仍然是当今聚合物科学和工程中最重要的问题之一。随着同步辐射X射线散射和衍射方法的出现，以及流变学和光散射技术的结合，许多根本重要的悬而未决的问题现在可以得到适当的解决。众所周知，聚合物加工过程中流动引起的分子取向对结晶动力学以及最终聚合物的形态和性能都有很大的影响。在拟议的研究中获得的知识将显著提高我们理解包含晶体组分的多组分体系中结构、相行为、过程和性质之间的关系的能力。这些信息将导致改进的聚合物工艺和新的聚合物产品的开发，从而使特定的聚合物行业和整个社会受益。这一提议的更广泛影响有几个。直接的好处是，拟议的活动将在学术机构和政府机构(即，石溪大学、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，并获得跨学科研究经验。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。他们还将参与石溪和布鲁克海文国家实验室的暑期研究项目，在那里他们将监督高中生和本科生以及工业科学家进行同步辐射X射线实验和相关的实验室研究。

TECHNICAL SUMMARY:The proposed research aims to investigate several newly discovered phenomena of orientation-induced crystallization precursor structures in multi-component polymer melts under flow. The phenomena include (1) formation of precursor structures at both nanoscopic and macroscopic scales, which can act as multi-scaled scaffolds to guide the crystallization process, and (2) the relationships among the flow-induced precursor structures, rheological behavior, multi-component phase behavior and type of flow field. To tackle the proposed problems, following research plans have been composed. First, the chosen multi-component systems, all based on polyolefin will include polymer blends of model compounds (e.g. high molecular weight crystallizable species and low molecular weight non-crystallization species), segmental olefin block copolymers (with only one crystallizable block) and polyolefin nanocomposites with well dispersed surface-modified carbon nanofibers/nanotubes. Second, to understand the rheological behavior, experimental data in dynamic and transient modes will be described by a GEX-based model in order to yield relaxation mechanisms responsible for the formation of precursor structure. Third, the development of structure in real time will be following by the use of combined methods including rheology, in-situ synchrotron small-angle-X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) and light scattering techniques. Finally, to understand the effect of different flow fields, results from simple shear (containing the rotational element) and extensional flow (without the rotational element) will be compared.NON-TECHNICAL SUMMARY:The subject of flow-induced crystallization, especially in multi-component systems such as polymer blends, block copolymers and nanocomposites, remains to be one of the most important problems in polymer science and engineering today. With the availability of synchrotron X-ray scattering and diffraction methods, and the coupling of rheology and light scattering techniques, many unanswered questions of fundamental importance can now be suitably addressed. It is known that molecular orientation induced by flow during polymer processing operations can deeply affect the crystallization kinetics as well as the final polymer morphology and properties. The knowledge obtained in the proposed study will significantly enhance our ability to understand the relationships between structure, phase behavior, process and property in multi-component systems containing crystalline components. The information will lead to developments of improved polymer processes and new polymer products, thus benefiting the polymer industry in specific and the society in general. The broader impacts of this proposal are several. The immediate benefit is that the proposed activities will produce tight links between academic and government institutions (i.e., Stony Brook University, National Synchrotron Light Source). Students and scientists will be trained in both institutions and receive interdisciplinary research experiences. 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 and Brookhaven National Laboratory summer research programs, where they will supervise high school and undergraduate students as well as industrial scientists to carry out synchrotron X-ray experiments and related in-laboratory studies.