DMREF: Tuning Liquid Crystallinity in Conjugated Polymers to Simultaneously Enhance Charge Transport and Control Mechanical Properties

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Non-technical Description: The proposed computationally-guided approach will provide an accelerated materials design framework useful for both academic and industrial efforts to accelerate the development of conjugated polymers for flexible electronics. The work is designed to leverage progress in the prediction and measurement of fundamental properties of conjugated polymers, and move forward along the materials development continuum. Key efforts integrate theory, simulations, and experiments, both through the development of new tools and by refining concepts of how microstructure governs charge transport in conjugated polymers. Furthermore, the Principal Investigators will develop an ambitious outreach pilot program that uses research activities as tools for improving educational opportunities and outcomes for students at non-PhD institutions (such as community colleges). Penn State is a unique microcosm of the broader higher education ecosystem, because it consists of a central research-intensive campus that is integrated with 19 largely two-year commonwealth campuses serving more diverse student populations - making Penn State an ideal incubator to explore the use of research as a recruiting and retention tool. In collaboration with the Leonhard Center for the Enhancement of Engineering Education at Penn State, the proposed work will establish a data-driven program to translate computational tools from the proposed technical objectives into web-based research experiences targeting Science, Technology, Engineering, and Mathematics (STEM) students at Penn State commonwealth campuses. Technical Description: The work within this proposal leverages previous advances to predict the persistence length, glass transition temperature and nematic-to-isotropic transition temperature. The proposed project aims to further advance computational materials design, by developing tools capable of accelerating the prediction of mechanical and conductive properties. Three computational tools will be developed: coarse-grained models based on force-matching to accelerate computational design of liquid crystalline semiflexible polymers, chain-shrinking simulations to predict the effect of liquid crystallinity on entanglement, and tight-binding models to explore the role of packing and disorder on charge transport. The combination of simulations and experiments will be crucial to generate accurate coarse-grained simulations capable of predicting liquid crystallinity through the Principal Investigators' approach that combines molecular dynamics simulations with self-consistent field theory calculations. This will enable the systematic computational exploration of backbone and side chain architectures that are validated with selected synthesized model materials. Simulations and experiment will also be crucial to incorporate nematic order in the Principal Investigators' unified theory of polymer entanglements, and thereby provide a tool capable of predicting rheological properties (e.g. mechanical properties) of conjugated polymers from the chemical structure. Furthermore, tight-binding models will predict the role of packing and local disorder on charge transport, to explore the hypotheses that layered disordered phases can play a crucial role in promoting efficient charge transport by facilitating pi-stacking. Such models will be validated by measurements of the charge mobility as a function of temperature and within various crystalline, liquid crystalline, or isotropic phases.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.