Understanding the Mobile Oriented Amorphous Fraction in Semicrystalline Ferroelectric Polymers and Its Unique Contribution to Electrostriction

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NON-TECHNICAL SUMMARY:Flexible hybrid electronics are in high demand for various applications, including the internet of things, human performance monitoring, wearable medical sensors, energy harvesting, and soft robotics. Among the many electroactive polymers, electrostrictive polymers exhibit many unique and appealing attributes. This project incorporates an integrated experimental/theoretical approach to understand the fundamental physics of electrostriction in polar semicrystalline polymers. It is proposed that the liquid-crystal-like oriented amorphous fraction contributes significantly to the electrostrictive actuation. Capitalizing on this hypothesis, a closed loop of theoretical prediction, synthesis, and property characterization will be implemented to obtain fundamental understanding and accelerate the discovery of new materials. In addition, this project will also integrate education and outreach in science, technology, engineering, and mathematics. This will include summer research opportunities for undergraduates and high school students. TECHNICAL SUMMARY:In response to the fast development of flexible electronics, this project aims to understand the origin of electrostriction and develop new electrostrictive polymers for better performance. Recently, a unique component in the complex semicrystalline morphology of ferroelectric polymers, i.e., the liquid-crystal-like oriented amorphous fraction (OAF), was identified. Unlike the ferroelectric crystals, these highly mobile OAFs can actuate at a much lower electric field via a field-induced conformational transformation (i.e., mechanoelectrostriction) and the electric repulsion of aligned ferroelectric domains. In this project, computer simulation with full-atomistic and coarse-grained molecular dynamics will first be used to unravel both the mechanoelectrostriction and the electric repulsion mechanisms and to understand their theoretical limits. This information will guide the experimental preparation of electrostrictive polymers, including both poly(vinylidene fluoride)-based random copolymers/terpolymers and relaxor-like n-nylon copolymers. In-situ X-ray diffraction during electric poling will be performed to understand the complex semicrystalline morphology and differential contributions from the crystallites and the OAFs. The experimental findings will be fed back to the computer simulation for refinement. Through this cycle of computer simulation, synthesis, structure/property characterization, and feedback, enhanced electrostriction in ferroelectric polymers will be fully understood, and new electroactive materials will be implemented..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.