Giant spontaneous polarization for enhanced ferroelectric properties of biaxially oriented poly(vinylidene fluoride) by mobile oriented amorphous fractions

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2021-01, Vol.9 (3), p.894-97
• Main Authors: Rui, Guanchun, Huang, Yanfei, Chen, Xinyue, Li, Ruipeng, Wang, Dingrui, Miyoshi, Toshikazu, Zhu, Lei
• Format: Article
• Language: English
• Subjects: Beta phase; Copolymers; Crystal structure; Crystallinity; Density functional theory; Electroactive polymers; Ferroelectric materials; Ferroelectricity; Fluorides; Hysteresis loops; Polarization; Polystyrene resins; Polyvinylidene fluorides; Robotics; Vinylidene fluoride
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d0tc04632a

Poly(vinylidene fluoride) (PVDF) and its random copolymers exhibit the most distinctive ferroelectric properties; however, their spontaneous polarization (60-105 mC m −2 ) is still inferior to those (>200 mC m −2 ) of the ceramic counterparts. In this work, we report an unprecedented spontaneous polarization ( P s = 140 mC m −2 ) for a highly poled biaxially oriented PVDF (BOPVDF) film, which contains a pure β crystalline phase. Given the crystallinity of ∼0.52, the P s for the β phase ( P s,β ) is calculated to be 279 mC m −2 , if a simple two-phase model of semicrystalline polymers is assumed. This high P s,β is invalid, because the theoretical limit of P s,β is 185 mC m −2 , as calculated by density functional theory. To explain such a high P s for the poled BOPVDF, a third component in the amorphous phase must participate in the ferroelectric switching to contribute to the P s . Namely, an oriented amorphous fraction (OAF) links the lamellar crystal and the mobile amorphous fraction. From the hysteresis loop study, the OAF content was determined to be ∼0.28, more than 50% of the amorphous phase. Because of the high polarizability of the OAFs, the dielectric constant of the poled BOPVDF reached nearly twice the value of conventional PVDF. The fundamental knowledge obtained from this study will provide a solid foundation for the future development of PVDF-based high performance electroactive polymers for wearable electronics and soft robotic applications. Oriented amorphous fraction in biaxially oriented poly(vinylidene fluoride) gives it significantly enhanced dielectric and ferroelectric properties.