Nucleation Control of Conjugated Polymers through Melt-Crystallization and Self-Seeding

非技术概述：半晶共轭聚合物是一类导电材料，目前正在研究中，用于柔性电子，太阳能电池，发光二极管和传感器。在这些聚合物中形成的形态由加工条件决定，并决定了最终的电子、光学和机械性能。共轭聚合物通常是通过使用有机溶剂来加工的，使用有机溶剂会引起环境问题。相比之下，熔体加工很少受到关注，因此熔体状态结晶的基本机制和这些聚合物可以获得的形态类型仍然知之甚少。在这里进行的研究有可能实现新的无溶剂方法来处理半结晶共轭聚合物，其对环境的影响比溶液处理的对应物小，并提供在溶剂存在下无法通过结晶获得的新形态（和因此的性质）。本项目探索如何利用分子属性和熔体加工方法来操纵结晶过程和由此产生的半结晶结构。该项目还将通过积极招募女性和少数民族学生，寻求扩大代表性不足的群体对科学的参与，并将通过研究机会培养本科生。它还将涉及在学术和工业环境中具有重要价值的领域培训研究生。这项研究的结果将通过在有关期刊上发表、在会议上发表以及在网上提供材料和出版物等方式广泛传播。技术概述：该项目的目标是通过在静态和流动条件下通过自播种操纵其成核行为来控制基准共轭聚合物的熔融结晶过程。为此，将探讨熔融结晶过程中的成核和生长过程以及分子属性和加工变量的相互作用。所获得的知识将允许通过无溶剂加工方法控制和优化所得到的半晶形态（这是优化性能的关键）。这项提议的工作具有双重意义。一方面，它将推进共轭聚合物熔融结晶机理的基础知识，提供对成核和结晶生长的步骤的见解，从熔融状态结晶过程中形成的详细形态，以及聚合物分子属性和明确的加工条件的具体作用。所获得的知识将有助于建立共轭聚合物和经典绝缘聚合物的基本熔融结晶过程之间的相似性和差异性。另一方面，本项目将探索如何通过无溶剂处理和选择聚合物链特征（特别是分子量和分子量分布），在静态和流动条件下通过操纵成核步骤来定制半结晶形态。期望一些控制传统聚合物熔体成核的方法也适用于共轭聚合物。因此，所提出的工作将最终提供一个框架，当共轭聚合物从其熔融状态直接结晶时，可以控制半结晶形态。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY: Semicrystalline conjugated polymers are a class of electrically conductive materials currently in research for use in flexible electronics, solar cells, light-emitting diodes, and sensors. The morphology that develops in these polymers is determined by processing conditions and dictates final electronic, optical, and mechanical properties. Conjugated polymers are typically processed through utilization of organic solvents, the use of which poses environmental concerns. In contrast, melt-processing has received little attention, so the fundamental mechanism of crystallization from the melt state and the types of morphologies that can be attained for these polymers remain poorly understood. The research to be conducted here has potential to enable new solvent-free approaches for processing semicrystalline conjugated polymers with less environmental impact than their solution-processed counterparts, and to provide access to novel morphologies (and thus properties) not attainable through crystallization in the presence of solvents. This project explores how molecular attributes and melt-processing approaches can be employed to manipulate the crystallization process and the resulting semicrystalline structure. This project will also seek to broaden participation of underrepresented groups in science by actively recruiting female and minority students, and will result in training of undergraduate students through research opportunities. It will also involve training of graduate students in a field of great value in both academic and industrial settings. Results of this research will be broadly disseminated by publishing in relevant journals, presenting at conferences, and making materials and publications available online. TECHNICAL SUMMARY:The objective of this project is to control the melt crystallization process of a benchmark conjugated polymer by manipulating its nucleation behavior through self-seeding both under quiescent and flow conditions. For this purpose, the processes of nucleation and growth and the interplay of molecular attributes and processing variables during melt-crystallization will be explored. The obtained knowledge will allow control and optimization of the resulting semicrystalline morphology (which is key to optimizing properties) through solventless processing methods. The significance of the proposed work is two-fold. On one hand, it will advance fundamental knowledge of the mechanism of melt-crystallization of conjugated polymers, providing insight into the steps of nucleation and crystalline growth, the detailed morphologies that develop during crystallization from the melt state, and the specific role of polymer molecular attributes and well-defined processing conditions. The acquired knowledge will serve to establish similarities and discrepancies between the basic melt crystallization process of conjugated polymers and that of classical insulating polymers. On the other hand, this project will explore how solvent-free processing and selection of polymer chain characteristics (particularly molecular weight and molecular weight distribution) can be used to tailor semicrystalline morphology through manipulation of the nucleation step under quiescent and flow conditions. It is expected that some approaches developed for control of nucleation in traditional polymer melts may be applicable to conjugated polymers as well. Therefore, the proposed work will ultimately provide a framework that allows control of semicrystalline morphology when a conjugated polymer is crystallized directly from its melt state.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.