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

非技术综述：半晶共轭聚合物是目前正在研究的一类导电材料，用于柔性电子产品、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进行加工的，有机溶剂的使用会引起环境问题。相比之下，熔融加工很少受到关注，因此这些聚合物从熔融状态结晶的基本机制和可以获得的形态类型仍然知之甚少。将在这里进行的研究有可能实现新的无溶剂方法来加工半结晶共轭聚合物，而对环境的影响比溶液加工的同类聚合物要小，并提供在有溶剂的情况下无法通过结晶获得的新的形态(从而性能)。这个项目探索了如何使用分子属性和熔融加工方法来操纵结晶过程和由此产生的半晶体结构。该项目还将通过积极招收女学生和少数族裔学生，寻求扩大代表性不足群体对科学的参与，并将通过研究机会对本科生进行培训。它还将包括在学术和工业环境中具有重要价值的领域对研究生进行培训。这项研究的结果将通过在相关期刊上发表、在会议上发表以及在网上提供材料和出版物的方式广泛传播。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控制基准共轭聚合物的成核行为来控制其熔融结晶过程。为此，将探索成核和生长过程，以及熔融结晶过程中分子属性和工艺变量的相互作用。所获得的知识将允许通过无溶剂加工方法来控制和优化所得到的半晶形态(这是优化性能的关键)。这项拟议工作的意义是双重的。一方面，它将促进对共轭聚合物熔融结晶机理的基础知识，洞察成核和结晶生长的步骤，熔融状态下结晶过程中形成的详细形态，以及聚合物分子属性和明确定义的加工条件的具体作用。所获得的知识将有助于确定共轭聚合物的基本熔融结晶过程与经典绝缘聚合物的基本熔融结晶过程之间的异同。另一方面，该项目将探索如何使用无溶剂加工和选择高分子链特征(特别是相对分子质量和分子量分布)，通过操纵静态和流动条件下的成核步骤来定制半结晶形态。为控制传统聚合物熔体中的成核作用而开发的一些方法有望同样适用于共轭聚合物。因此，拟议的工作最终将提供一个框架，允许在共轭聚合物直接从其熔融状态结晶时控制半结晶形态。这一奖项反映了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。

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.