EAGER: Fluid-directed Multiscale Assembly of Conjugated Polymers

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NON-TECHNICAL SUMMARY:Over the past half century electronic materials have changed the way we live, and in the coming decades they may revolutionize the way we harvest energy as well. However, electronic products are presently manufactured by processes of high energy and environmental cost. In comparison, polymer-based electronics (i.e., using ultra-thin films of specialty plastic materials) can be processed from solutions at low temperatures by low-cost, high-throughput methods such as roll-to-roll printing. Controlled assembly of materials and the way their morphological features evolve during processing has played a central role in a broad range of areas ranging from electronics, pharmaceuticals, food, fine chemicals, energy materials, etc. The approach in this project represents a new methodology for controlling assembly of functional materials by designing the fluid flow used in their processing. Using a hypothesis-driven approach, it is aimed at providing new fundamental insights and design rules on fluid-directed assembly that could have broad implications across numerous areas.The planned work will integrate research efforts with outreach and educational activities. These activities will include outreach to high-school students, aiming particularly to increase the interest and participation of girls in science, engineering, and technology. Undergraduate students will be mentored and research projects pertinent to directed assembly and polymer crystallization and aggregation will be designed for their engagement. Also, this project will impact new course development on fundamental principles of directed assembly of molecular solids. The course will be designed for graduate students and will include modules on organic semiconductors and alternative energy.TECHNICAL SUMMARY:A key challenge in realizing high-performance conjugated-polymer based semiconductors is to direct their assembly from molecular, meso-, to macroscale during the solution printing process. To address this challenge, the PI proposes a new method of fluid-directed assembly to control the morphology of printed conjugated-polymer thin films across multiple length scales. She will implement this methodology by designing the fluid flow on the platform of microfluidic slot-die printing. Specifically, at the molecular scale the aim is to induce local ordering in molecular aggregates by introducing extensional flow to promote polymer nucleation and pre-aggregation. At the mesoscale the objective is to control orientation and alignment of polymer pre-aggregates by designing the shear flow. The PI will further investigate the role of molecular rigidity in flow-induced polymer crystallization and establish the relationship between morphology and charge transport in semiconducting polymers.The proposed approach will be implemented by combining experiments on polymer crystallization and aggregation, simulations of fluid flow, and theory on fluid-polymer interactions. This approach can enable directed molecular assembly across multiple length scales. Attaining multiscale assembly at once is highly challenging but critical to controlling solid-state properties, such as in the case of printed electronics. Furthermore, the proposed approach will help to unravel the morphology-charge transport relationships for semiconducting polymers. Establishing this relationship has been challenging due the lack of methodologies for systematically tuning the thin film morphology across multiple length scales.