Microstructures and Ferroelectric Properties of Poly(vinylidene fluoride-ter-trifluoroethylene-ter-vinyl fluoride) Terpolymers

The incorporation of comonomers as structural defectshas beenextensively exploited to modulate the structures and physical propertiesof poly-(vinylidene fluoride) (PVDF)-based ferroelectric polymers.Previous studies have shown that the large-sized comonomers can inducerelaxor ferroelectricity in the PVDF-based terpolymers as a resultof the stabilization of the helical conformation. Here, we show that,with incorporating a small-sized defect, vinyl fluoride (VF), intothe copolymer, the resulting terpolymers preferentially adopt thepolar all-trans conformation, as revealed by the structural characterizationsand confirmed by density functional theory simulations. Consequently,the terpolymers exhibit robust ferroelectricity with an increasedferroelectric-to-paraelectric transition temperature and a highercoercive field as the VF content increases. This work systematicallyinvestigates the compositional dependence of the microstructures,crystalline structures, and ferroelectric and electromechanical propertiesof the terpolymers and stresses the vital role of comonomer size intailoring the structures and properties of ferroelectric polymers.