Enhancing Piezoelectricity in Semicrystalline Ferroelectric Polymers via Electrostriction of the Oriented Amorphous Fraction

NON-TECHNICAL SUMMARY:

Piezoelectric polymers are unique materials that generate electricity when they are compressed or stretched. Since their discovery in 1969, they have shown great promise for use in important technologies, including sensors, transducers, actuators, and energy harvesters. However, their adoption has been limited by their low performance when compared to piezoelectric ceramics, which are predominantly used today.

This project addresses a key scientific question: how do piezoelectric polymers work at the molecular level? Specifically, which part of these semicrystalline polymers contributes primarily to the observed piezoelectricity - the crystalline regions, the amorphous regions, or the interphase between the two? To tackle this challenge, the project will employ computer simulation, advanced polymer processing, structural analysis, and property characterization to uncover the mechanisms behind polymer piezoelectricity.

With the resolution of this fundamental question, researchers would be able to develop advanced piezoelectric polymers that can rival, or even exceed, the performance of piezoelectric ceramics. The products of this research could have far-reaching impacts. High-performance piezoelectric polymers could enable more efficient and lightweight medical devices for ultrasound imaging and therapy, enhance wearable electronics, and drive innovations in robotics.

Beyond the scientific benefits, this project prioritizes education and outreach to inspire and train the next generation of scientists and engineers. It also includes hands-on research opportunities for high school and undergraduate students. TECHNICAL SUMMARY:

Since the discovery of chain-folding in single lamellar crystals, a two-phase model (i.e., crystalline and amorphous phases) has been used to describe semicrystalline polymers. However, for melt- and solid state-processed semicrystalline polymers, studies using temperature-modulated differential scanning calorimetry have revealed a third component: the rigid amorphous fraction (RAF).

It is suggested that chain-folding may not be the predominant packing scheme for these materials. Instead, a substantial portion of the polymer chains extends directly from the crystalline basal planes, forming an oriented amorphous fraction (OAF) that gradually transitions into the isotropic amorphous fraction (IAF). The tethering of OAF to rigid crystals results in reduced mobility, making it an RAF.

By integrating computer simulation and experimental studies, this project aims to elucidate the OAF structure in semicrystalline ferroelectric polymers, such as poly(vinylidene fluoride) (PVDF). It is hypothesized that the electrostrictive OAF is the major contributor to the piezoelectric property. Initially, computer simulation will be used to calculate the structural factor of OAF in PVDF and compare it with the experimental X-ray diffraction patterns to gain insights into the OAF structure.

Subsequently, a revised nanocomposite model, consisting of crystals, OAF and IAF will be utilized to simulate the piezoelectric response. Additionally, nanocrystalline PVDF will be explored to increase the OAF content and enhance the piezoelectricity. Finally, multiblock copolymers, composed of ferroelectric copolymers and electrostrictive terpolymers of PVDF, will be synthesized to investigate new opportunities.

The goal of this research is an improved fundamental understanding of the structure-piezoelectric property relationship in semicrystalline ferroelectric polymers.

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.