Nature of Ferroelectric Behavior in Main-Chain Dipolar Glass Nylons: Cooperative Segmental Motion Induced by High Poling Electric Field

摘要

Main-chain dipolar glass polymers such as aromatic nylons are promising for high energy density and low loss dielectric applications because of the limited, noncooperative oscillation of highly dipolar amide groups. However, quenched aromatic nylons have been reported to exhibit significant ferroelectric switching upon high field poling. It is desirable to suppress ferroelectric switching for electric energy storage application, and this requires a fundamental understanding of the nature of ferroelectric behavior in dipolar glass nylons. In this work, a nearly 100% amorphous aromatic nylon, Selar, was used to investigate the origin of ferroelectricity in glassy nylons. Using Fourier transform infrared spectroscopy, it was found that hydrogen-bonding strength played an important role in the ferroelectric switching of amide dipoles in the loosely packed glassy matrix. When hydrogen bonding was weak such as in the quenched film, significant ferroelectric switching took place. In contrast, quenched and annealed films did not exhibit any ferroelectric switching. High-voltage broadband dielectric spectroscopy was used to study molecular and segmental motions in Selar. It was observed that the primary contribution to ferroelectric switching came from cooperative segmental motions (i.e., a combination of various sub-T-g relaxations, where T-g is the glass transition temperature) in the main-chain dipolar glass nylon. This understanding will help us design new aromatic nylons with suppressed segmental motions for high energy density and low loss dielectric applications.