CAREER: Multiscale Assembly of Conjugated Polymers at Dynamic Reconfigurable Interfaces

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NON-TECHNICAL SUMMARYControlled assembly of electrically active materials has been a cornerstone to the electronics and energy industries. Recent years have witnessed a surge of semiconducting polymers which promise diverse applications from flexible electronics and transparent solar cells to imperceptible medical devices. However, it remains a central challenge to control the assembly of semiconducting polymers from the molecular to the device scales, which critically impact their device performance. This research addresses this challenge by developing dynamic, reconfigurable interfaces to direct the assembly of semiconducting polymers into highly ordered structures across length scales. The fundamental mechanism of surface-directed polymer assembly will be elucidated to guide the design of such interfaces. This approach, inspired by how biominerals (e.g. bone) are formed, is in contrast to conventional approaches wherein highly ordered, rigid surfaces are employed to direct assembly of electronic materials. This work may ultimately enable high-performance, low-cost printed electronic, energy and biomedical devices in forms that seamlessly interact with the human body and the living environment, which would have impact on the electronic, energy and healthcare industries. The fundamental insights from the planned work can be further extended to areas beyond semiconducting polymers, given the broad applicability of surface-directed assembly to the manufacturing of a wide range of functional materials. The educational activities of the project are integrated with the research component, aiming at narrowing the gap between increasing demand in high-tech workforce and limited enrollment in STEM education in the US. Both polymer sciences and electronics have been at the center stage of high-tech industries. The overarching goal is to attract, nurture and retain STEM talents, particularly women, through public engagement, educational outreach, undergraduate and graduate education. TECHNICAL SUMMARYThis research aims to elucidate the fundamental mechanisms of interfacially-driven assembly of conjugated polymers from the molecular to centimeter scale, and to develop a new dynamic templating approach to achieve polymer assemblies with prescribed order and controlled properties. Although it is known that the multiscale morphology of conjugated polymers (molecular conformation/packing, mesoscale domain size/orientation, macroscale crystallinity/alignment) can modulate the electronic, optical, and mechanical properties by orders of magnitude, it remains a central challenge to assemble conjugated polymers into highly ordered structures across multiple length scales. This project will provide better understanding of the assembly mechanism of semi-rigid donor-acceptor conjugated polymers, which exhibit distinct assembly behavior from the well-studied flexible polymers. The planned work focuses on a particularly important problem in this area: to elucidate the role of interfaces in directing conjugated polymer assembly, considering the predominance of surface-induced nucleation during thin-film deposition from solution. A key aspect that distinguishes this work from previous research is the focus on dynamic, reconfigurable interfaces. This approach is inspired by dynamic, cooperative assemblies ubiquitous in biological systems, which require minimal energy input to attain exquisite structures across length scales. Using a hypothesis-driven approach, this research will provide new fundamental insights on polymer assembly at dynamic, reconfigurable interfaces by complementing in-situ multiscale structural characterizations with free-energy modeling based on nucleation theory. This study will lead to fundamentally new insights on macromolecular assembly -- a subject at the heart of materials research. Many polymer assembly processes take place at interfaces due to generally lower free energy barriers, whereas the mechanism of surface-directed assembly process is much less understood; this is a challenge that this work ultimately addresses.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.