CAREER: Nanoscale Resolution of Near-Interface Crystallization in Multicomponent Semicrystalline Polymeric Materials

第一部分：非技术概述半结晶聚合物约占所有合成塑料的70%，它们广泛存在于日常生活中的包装、运输和微电子等高科技应用中。半结晶聚合物通常以多组分聚合物材料的形式使用，例如用于包装的多层聚乙烯/聚对苯二甲酸乙二酯薄膜和用于运输的碳纤维增强复合材料。这些多组分材料的一个主要特征是存在大量的聚合物/聚合物或聚合物/填料界面。了解这些界面对聚合物结晶的影响对于预测具有所需结晶结构和性能的多组分材料至关重要。不幸的是，缺乏这样的基本理解。该项目将致力于利用一种具有纳米级空间分辨率的新荧光技术，缩小界面效应和聚合物结晶方面的基础知识差距。从这项研究中获得的基础知识将推动具有优化晶体结构和性能的新的多组分材料的开发，这将有助于广泛的应用，如食品包装和生物医学设备。该项目将为研究生、本科生和高中生提供综合研究和教育体验，包括服务不足群体的成员。首席调查员和学生还将开发面向教育的在线视频和动手演示，以吸引公众参与并吸引K-12学生进入STEM领域。第二部分：技术总结本项目的研究目标是利用一种新的纳米级空间分辨率的荧光技术，促进对多组分半结晶聚合物结晶过程中界面效应的基本了解。首席研究员(PI)计划通过战略性地将痕量的“报告”(即晶体传感)荧光染料标记放置在距界面的受控距离处来实现这一目标，以获得关于局部结晶的基于荧光的信息，从而获得界面效应。为了实现这一目标，PI和学生们将进行三项研究：(1)通过选择性地将染料放置在刚性和可移动的无定形部分区域来了解荧光作为结晶传感机制的作用，以了解它们对整体荧光的贡献；(2)通过特定位置的荧光和互补方法，如掠入射X射线散射，研究近界面结晶；(3)揭示聚合物/聚合物和聚合物/基质界面对结晶的影响及其扰动长度尺度。材料研究将集中在可降解聚L-乳酸(PLLA)作为一种模型半结晶聚合物，以推动基于PLLA的新型多组分材料的设计，这些材料具有所需的结构/性能和更好的可持续性，包括多层膜、复合材料、共混物和嵌段共聚物。该教育/推广计划将在多个层面上扩大这一职业研究的范围和好处：(1)PI和学生将通过关于半晶体聚合物的在线教育视频接触到普通公众；(2)PI将开发一个关于塑料包装的新实验模块，并利用亚利桑那州立大学现有的研究计划，培训研究生、本科生和高中生有关聚合物合成和表征的知识；(3)国际学生协会和学生将在亚利桑那州立大学的大门上进行动手演示，以激发当地K-12学生对聚合物和STEM职业的兴趣。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYSemicrystalline polymers comprise ~70% of all synthetic plastics, and they are pervasive in daily life in packaging, transportation, and high-technology applications like microelectronics. Semicrystalline polymers are often used in the form of multicomponent polymeric materials, e.g., multilayer polyethylene/poly(ethylene terephthalate) films for packaging and carbon fiber-reinforced composites for transportation. A key feature of these multicomponent materials is the presence of a large quantity of polymer/polymer or polymer/filler interfaces. Understanding the effects of these interfaces on polymer crystallization is essential to the predictive design of multicomponent materials with desired crystalline structures and properties. Unfortunately, such a fundamental understanding is lacking. This project will work toward closing the fundamental knowledge gap in interfacial effects and polymer crystallization, using a new fluorescence technique with a nanoscale spatial resolution. The fundamental knowledge gained from this research will advance the development of new multicomponent materials with optimized crystalline structures and properties, which can contribute to a broad range of applications such as food packaging and biomedical devices. This project will provide an integrated research and educational experience for graduate students, undergraduate students, and high-school students, including members of underserved groups. The principal investigator and students will also develop education-oriented online videos and hands-on demonstrations to engage the general public and attract K-12 students into STEM fields. PART 2: TECHNICAL SUMMARYThis project’s research goal is to advance fundamental understanding of the interfacial effects on crystallization in multicomponent semicrystalline polymers, using a new fluorescence technique with a nanoscale spatial resolution. The principal investigator (PI) plans to achieve this goal by strategically placing trace amounts of “reporter” (i.e., crystal-sensing) fluorescent dye labels at controlled distances from interfaces to elicit fluorescence-based information about local crystallization and thus interfacial effects. Towards this goal, the PI and students will pursue three research thrusts: (1) Understand the role of fluorescence as a crystallization-sensing mechanism by selectively placing the dyes in rigid vs. mobile amorphous fraction regions to deconvolute their contributions to the overall fluorescence; (2) Study near-interface crystallization by location-specific fluorescence and complementary methods such as grazing-incidence X-ray scattering; (3) Unveil polymer/polymer and polymer/substrate interfacial effects on crystallization and their perturbation length-scale. Material studies will focus on degradable poly(L-lactic acid) (PLLA) as a model semicrystalline polymer to advance the design of new PLLA-based multicomponent materials with desired structures/properties and improved sustainability, including multilayer films, composites, blends, and block copolymers. The education/outreach plan will broaden the reach and benefits of this CAREER research at multiple levels: (1) The PI and students will reach out to the general public through online educational videos on semicrystalline polymers; (2) The PI will develop a new lab module on plastic packaging and leverage the existing research programs at ASU to train graduate students, undergraduate students, and high-school students on polymer synthesis and characterization; (3) The PI and students will develop hands-on demonstrations at ASU Open Door to stimulate local K-12 students’ interest in polymers and STEM careers..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.