Influence of Steric Hindrance on Ferro‐ and Piezoelectric Performance of Poly(vinylidene fluoride)‐Based Ferroelectric Polymers

• Published in: Macromolecular chemistry and physics 2019-11, Vol.220 (21), p.n/a
• Main Authors: Li, Zhong, Liao, Jiani, Xi, Ziting, Zhu, Weiwei, Zhang, Zhicheng
• Format: Article
• Language: English
• Subjects: Beta phase; Copolymers; Crystal structure; Crystallinity; dielectrics; Electric properties; Ferroelectric domains; Ferroelectric materials; Ferroelectricity; ferroelectrics; Fluorides; Hydrophones; Medical electronics; Molecular conformation; Piezoelectricity; piezoelectrics; Polarity; poly(vinylidene fluoride‐tetrafluoroethylene); poly(vinylidene fluoride‐trifluoroethylene); Polyvinylidene fluorides; Properties (attributes); Steric hindrance; Vinylidene fluoride
• ISSN: 1022-1352; 1521-3935
• DOI: 10.1002/macp.201900273

Poly(vinylidene fluoride) (PVDF) and copolymers possess excellent ferro‐ and piezoelectric properties, and highly expected to be utilized as sensors in the areas covering the smart wearer, hydrophone, speaker, and medical ultrasonic devices. Besides PVDF in β crystalline phase, the copolymers with trifluoroethylene (TrFE) and tetrafluoroethylene (TFE) are widely investigated both in academia and industry. To illustrate how the steric hindrance between VDF and TrFE/TFE affects the condensed‐state structure and electric properties of the polymers, the electric properties and their dependences on molecular configuration and crystal structures of PVDF, P(VDF‐TrFE), and P(VDF‐TFE) are comparatively investigated. The introduction of same molar contents (20 mol%) of TrFE and TFE monomers into PVDF chain leads to the similar conformation transformation from α (γ ) phase to β phase and similar crystallinity in resultant P(VDF‐TFE) and P(VDF‐TrFE) thanks to the depressed energy of trans conformation and the increased energy barrier between anti‐gauche and trans conformation. That leads to the more preferred β‐phase and ferroelectric domains generated in P(VDF‐TrFE) and P(VDF‐TFE). Both the size of ferroelectric phase, the polarity of the polymer chain, the organization and orientation of the grains along the field are responsible for the excellent piezoelectric field resulted by the varied composition as well. To illustrate how the steric hindrance between vinylidene fluoride (VDF) and trifluoroethylene (TrFE)/tetrafluoroethylene (TFE) affects the properties of the polymers, poly(vinylidene fluoride) (PVDF), P(VDF‐TrFE), and P(VDF‐TFE) are compared in this work. It is confirmed that TrFE and TFE may stabilize the trans conformation of PVDF, which is responsible for the preferred ferroelectric phase obtained in the copolymers.