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

半晶聚合物占所有合成塑料的70%，在日常生活中的包装、运输和微电子等高科技应用中无处不在。半结晶聚合物通常以多组分聚合材料的形式使用，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关键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具有理想晶体结构和性能的多组分材料的预测设计至关重要。不幸的是，我们缺乏这样一种基本的理解。该项目将致力于利用纳米级空间分辨率的新型荧光技术，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型多组分材料的发展，这将有助于食品包装和生物医学设备等广泛应用。该项目将为研究生、本科生和高中生，包括服务不足群体的成员提供综合研究和教育经验。首席研究员和学生们还将开发以教育为导向的在线视频和实践演示，以吸引公众并吸引K-12学生进入STEM领域。本项目的研究目标是利用纳米级空间分辨率的新型荧光技术，促进对多组分半晶聚合物中界面对结晶作用的基本理解。首席研究员（PI）计划通过战略性地将微量的“报告”（即晶体传感）荧光染料标签放置在距离界面的受控距离上来实现这一目标，以获得有关局部结晶和界面效应的基于荧光的信息。为了实现这一目标，PI和学生将追求三个研究重点：(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，以反卷曲它们对整体荧光的贡献，了解荧光作为结晶感应机制的作用；(2)利用定位荧光和掠入射x射线散射等互补方法研究近界面结晶；(3)揭示聚合物/聚合物和聚合物/衬底界面对结晶的影响及其微扰长度尺度。材料研究将集中于可降解聚l -乳酸（PLLA）作为一种模型半结晶聚合物，以推进基于PLLA的新型多组分材料的设计，这些材料具有理想的结构/性能和改进的可持续性，包括多层薄膜、复合材料、共混物和嵌段共聚物。教育/推广计划将在多个层面上扩大这项职业研究的范围和效益：(1)PI和学生将通过半结晶聚合物的在线教育视频与公众接触；(2) PI将开发一个新的塑料包装实验室模块，并利用亚利桑那州立大学现有的研究项目来培训研究生、本科生和高中生的聚合物合成和表征；(3)项目负责人和学生将在亚利桑那州立大学开放日进行实践演示，以激发当地K-12学生对聚合物和STEM职业的兴趣。该奖项反映了美国国家科学基金会的法定使命，并通过基金会的智力价值和更广泛的影响审查标准进行了评估，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.