Crystal Orientation and Temperature Effects on Double Hysteresis Loop Behavior in a Poly(vinylidene fluoride-<i>co</i>-trifluoroethylene-<i>co</i>-chlorotrifluoroethylene)-<i>graft</i>-Polystyrene Graft Copolymer

Recently, double hysteresis loop (DHL) behavior, which is advantageous for the high energy density and low loss dielectric application, was achieved in a poly­(vinylidene fluoride-<i>co</i>-trifluoroethylene-<i>co</i>-chlorotrifluoroethylene)-<i>graft</i>-polystyrene [P­(VDF-TrFE-CTFE)-<i>g</i>-PS­(14%)] graft copolymer due to the nanoconfinement effect. In this work, we continued to investigate the crystal orientation and temperature effects on the DHL behavior of this graft copolymer. Based on the electric displacement–electric field (D–E) study, crystal orientation had a profound effect on its electrical behavior. For the nonoriented sample, dielectric instead of ferroelectric behavior was observed. After uniaxial stretching, DHLs gradually developed in the oriented films upon increasing the extension ratio. For a fully stretched film, the DHL behavior was stable below 75 °C but gradually disappeared above 100 °C due to enhanced dc conduction and impurity ion migrational loss at elevated temperatures. After subtracting the dc conduction, D–E hysteresis loops from the ion loss were determined for the poling cycles below 100 MV/m. The hysteresis loss from ion migration under an applied field was closely related to ion concentration and diffusion coefficient, which were determined by broadband dielectric spectroscopy. Both parameters were used in a theoretical calculation to obtain hysteresis loops from ion migrational loss. By fitting the theoretical loops with those after dc conduction subtraction, ion mobility was found to be dependent upon both poling field and temperature. This study provides a quantitative understanding of the effects of impurity ions and dc conduction on dielectric and ferroelectric properties of polymers at elevated temperatures

Relaxor Ferroelectric Behavior from Strong Physical Pinning in a Poly(vinylidene fluoride-<i>co</i>-trifluoroethylene-<i>co</i>-chlorotrifluoroethylene) Random Terpolymer

Relaxor Ferroelectric Behavior from Strong Physical Pinning in a Poly(vinylidene fluoride-<i>co</i>-trifluoroethylene-<i>co</i>-chlorotrifluoroethylene) Random Terpolyme

Composite Poly(vinylidene fluoride)/Polystyrene Latex Particles for Confined Crystallization in 180 nm Nanospheres via Emulsifier-Free Batch Seeded Emulsion Polymerization

Recently, nanoconfined poly­(vinylidene fluoride) (PVDF) and its random copolymers have attracted substantial attention in research. In addition to the drastic change in crystallization kinetics, major interest lies in crystal orientation and polymorphism in order to understand whether enhanced piezoelectric and ferroelectric properties can be achieved. For example, PVDF has been two-dimensionally (2D) confined in cylindrical nanopores of anodic aluminum oxide (AAO) with various pore diameters. The crystal <i>c</i>-axis becomes perpendicular to the cylinder axes, which favors dipole switching in the impregnated AAO membrane. However, no polar phases have been obtained from 2D confinement even down to 35 nm pores after melt recrystallization. In this work, we realized three-dimensionally (3D) confined crystallization of PVDF in 180 nm nanospheres by employing a facile emulsifier-free batch seeded emulsion polymerization to prepare PVDF@polystyrene (PS) core–shell particles. Influences of polymerization temperature, PVDF/styrene feed ratio, and polymerization time were systematically investigated to achieve completely wrapping of PS onto PVDF particles and avoid the formation of Janus particles. Exclusive confined PVDF crystallization was observed in these core–shell composite particles. Intriguingly, after melt recrystallization, polar β/γ phases, instead of the kinetically favored α phase, were resulted from 3D confinement in 180 nm nanospheres. We attributed this to the ultrafast crystallization rate during homogeneously nucleated PVDF crystallization. For the first time, we reported that 3D confinement was more effective than 2D confinement in producing polar crystalline phases for PVDF