DMREF: Design Rules for Flexible Conductors: Predicting Chain Conformations, Entanglements, and Liquid Crystalline Phases of Conjugated Polymers

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Non-technical Abstract:Flexible electronic devices have the potential to transform our society, such as in distributed power, solid-state lighting, personal electronics, and biomedical devices. The objective of this program is to accelerate the development of conjugated polymers for flexible electronics. The project will generate tools to predict fundamental properties of conjugated polymers, such as the stiffness of the chain backbones, their ability to form liquid crystals, and the likelihood that chains will entangle, all from the chemical structure. As such, the combination of theory, simulation, and experiment will provide opportunities to refine design concepts in conjugated polymers and therefore create an accelerated materials design framework useful for both academic and industrial efforts. Beyond flexible electronics, developing a theoretical description for semiflexible polymers will be transformative across many applications of biopolymers, engineering thermoplastics, and liquid crystals. Furthermore, this program will create a pilot program aimed at improving the retention of students in STEM fields. Penn State's unique structure will be leveraged, where a large central campus is closely linked to smaller commonwealth campuses, to explore the use of remote research activities as a recruiting and retention tool. Technical Abstract: This program encompasses the development of three computational tools. Recent work by the PIs suggests a computationally inexpensive approach to predict the persistence length of conjugated polymers. The work of this program will validate this approach, with experimental measurements on synthesized polymers using neutron scattering in the melt or light scattering in dilute solution. Furthermore, the combination of simulations and experiments will generate values of the persistence length for various conjugated polymers that are of interest to the community. The PIs will also leverage their development of a new approach combining MD simulations and SCFT to predict the nematic coupling parameter and the nematic-to-isotropic transition temperature. Predictions of the phase behavior of various conjugated polymers that vary in stiffness will be compared with results from rheology, light microscopy and depolarized light scattering. Finally, the work will test scaling relationships for the entanglement length versus packing length, to predict the entanglement length of any conjugated polymer from the molecular structure, and test these predictions with rheological measurements. The combination of theory, simulation and experiment provides an opportunity to refine design concepts for conjugated polymers. Preliminary studies suggest that stiff chains align near interfaces, potentially enhancing charge transport in devices such as thin-film transistors that rely on transport near dielectric interfaces.