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

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

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.