Constraints in Semicrystalline Polymers During the Transition from the Liquid to the Solid State

技术综述：本研究项目将研究半结晶聚合物从液态向半结晶固态转变过程中的晶体约束效应。这项研究将回答以下关于结构和相对于限制的松弛动力学的具体问题。1.玻璃化转变时协同重排区域的长度xCRR是否与固相组分、晶组分或两者的发展相关？2.α驰豫(玻璃化转变)动力学是否与这些相同组分的发展相关？以及，3.在固化过程中生成的纳米相的结构是什么？对这些问题的回答将对半结晶聚合物的结晶和非结晶部分之间的关系提供一个基本的理解水平，因为限制发生在从液体到固态的转变过程中。这项研究的一个主要和新颖的方面将是使用反转热容量的准等温测量来研究形成晶体约束的时间发展。将分别评估固体部分和结晶部分的时间发展，从结晶的最早阶段，到球晶撞击，最后到结晶过程的完成。α驰豫(玻璃化转变过程)将用介电弛豫谱来研究，片层结构将用小角X射线散射和原子力显微镜来确定。非技术综述：塑料是日常生活中无处不在的材料。大多数商业上有用的塑料都是通过加热和加压来加工成所需的形状。一类重要的塑料包括那些在加工过程中也具有结晶能力的塑料。这些晶体的形状非常复杂，往往会形成簇状。但在一张非常简单的图片中，晶体的作用就像微型订书钉一样，在纳米尺度上将塑料结合在一起，防止组成分子四处移动。为了改善塑料的最终性能，重要的是：了解订钉形成的时间和方式；表征实际的晶体形状、大小和组织；并确定晶体如何限制其他分子的运动。这项研究将导致新的塑料产品和加工策略，提高我们的全球竞争力。该项目还服务于教育下一代科学家，特别关注聋哑人或重听学生。

TECHNICAL SUMMARY:The confining effect of crystals, during the transformation from liquid to semicrystalline solid of semicrystalline polymers, will be investigated in this research program. The research will answer the following specific questions about structure and relaxation dynamics vis--vis confinement. 1. Does the length, xCRR, of cooperatively rearranging regions, CRRs, at the glass transition correlate with the development of the solid fraction, the crystal fraction, or both? 2. Do the alpha relaxation (glass transition) dynamics vary in a manner correlated with the development of these same fractions? and, 3. What is the structure of the resultant nanophases during solidification? The answers to these questions will provide a fundamental level of understanding about the relationship between the crystals and the non-crystalline portions of the semicrystalline polymer, as confinement occurs during the transition from the liquid to the solid state. A major, and novel, aspect of this research will be the use of quasi-isothermal measurements of the reversing heat capacity to study the time development of formation of the crystal constraints. The time development of the solid fraction, and the crystalline fraction, respectively, will be assessed from the earliest stages of crystallization, through spherulite impingement, and finally to completion of the crystallization process. The alpha relaxation (glass transition process) will be studied using dielectric relaxation spectroscopy, and lamellar structure will be determined using small angle X-ray scattering and atomic force microscopy. NON-TECHNICAL SUMMARY:Plastics are ubiquitous materials in everyday life. The majority of commercially useful plastics are processed using heat and pressure to form them into desired shapes. An important class of plastics comprises those that also have the ability to crystallize during processing. The crystals have very complicated shapes, and tend to form in clusters. But in a very simplified picture, the crystals act like miniature staples, holding the plastic together on the nanometer length scale, and preventing the constituent molecules from shifting around. To improve the ultimate properties of the plastics, it is important to: understand when and how the staples form; characterize the actual crystal shape, size, and organization; and determine how crystals restrict the motion of the other molecules. This research will lead to new products and processing strategies for plastics, improving our global competitiveness. The program also serves to educate the next generation of scientists, with a special focus and outreach to students who are deaf or hard of hearing.