All-organic composites with strong photoelectric response over a wide spectral range

2-hydroxynaphthylidene-1′-naphthylamine(HNAN) and –NO_(2) modified HNAN(HNAN-NO_(2)) Schiff base compounds were synthesized and exhibited strong visible light absorption(<650 nm). These compounds were added to poly(vinylidene fluoride-trifluoroethylene)(P(VDF-Tr FE))ferroelectric polymer, obtaining composites with high photoelectric response under visible and infrared light. It was found that the modification of HNAN by the nitro group and the poling of the composites under a high electric field can greatly enhance the photoelectric response of the composites. The composites can generate high photovoltages of 1386 and352.7 mV under irradiation with near-infrared light(915 nm)and green light(532 nm). The mechanism of the photoelectric response of the composites under green light was explored and it was found that the response originates mainly from the coupling effect of the photothermal effect of the Schiff base and the pyroelectric effect of the ferroelectric polymer. The composites, which can be utilized as photodetector materials,are promising for next-generation artificial retina applications and the sensing capability of retina can be extended in a wide wavelength range from visible to infrared light.

Energy storage properties of PVDF terpolymer/PMMA blends

Dielectrics can be used to store electric energy in capacitors and high-energy density of the materials is desirable to reduce the size or weight of capacitors.To improve the energy storage properties of poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene)[P(VDF–TrFE–CFE)]terpolymer,P(VDF–TrFE–CFE)/poly(methyl methacrylate)(PMMA)blends were investigated in this study.By adding a small amount of PMMA into PVDF terpolymer(<5 wt%),the dielectric breakdown field of the blends can be improved as a result of the enhancement of elastic modulus of the blends.For the blends with<2.5 wt%PMMA,though their dielectric properties are reduced,under the same electric field,the energy density of the blends is almost the same as that of PVDF terpolymer.Consequently,the energy storage performance of the terpolymer can be improved by blending with a small amount of PMMA.

Large effective piezoelectric response from the spontaneously polarized surface layer in P(VDF-TrFE)arch films

In this work,we show that a d_(33)~150 pC/N can be obtained in nonpoled poly(vinylidene fluoride trifluoroethylene)(P(VDF-TrFE))copolymer films with an arch structure.The copolymer films,which are often thought to be homogeneous,are in fact inhomogeneous in microstructure and physical properties after film fabrication.Although a large proportion of the copolymer film is nonpolar,as expected in a nonpoled ferroelectric film,the surface regions of the film are spontaneously polarized.We propose that inhomogeneous stress in the surface regions,which is either from the constraint of the substrate or skin layer effect formed during the film fabrication,generates a flexoelectric response and orients the spontaneous polarization of the ferroelectric film.As a result of the polar surface regions,the nonpoled films exhibit a piezoelectric response.The piezoelectric response is further amplified by the special arch structure of the films,leading to the observed large effective piezoelectric response.This study not only discovers the polar surface effect in ferroelectric polymer films,but also proposes an approach to design polymer materials with a strong piezoelectric response.

Relaxor-like dielectric behavior and its effect on energy storage performance in P(TFE-HFP-VDF) terpolymers

Capacitors are critical components in many advanced electronic and electrical systems,such as pulse power systems,due to their fast charging-discharging speed and high power density[1-4].The ever-increasing demand for compact energy storage devices requires the dielectrics,which are the energy storage materials in capacitors,to have a higher energy density and low dielectric loss[2,3].Furthermore,a stable high-temperature performance is another important parameter to be considered for some applications in which high-temperature conditions are present,such as hybrid vehicles[4-7].

TUNING THE RESONANT FREQUENCIES OF FLEXURE MODE FLEXOELECTRIC PIEZOELECTRIC COMPOSITES

The newly developed flexure mode flexoelectric composites have extremely high direct piezoelectric response around mechanical resonant frequency.Methods of tuning the resonant frequencies of the composites were studied in this paper.The resonant frequencies can be adjusted by changing dimensions of ferroelectric ceramic bars in the composites or by adding an additional mass on the composites.Design of flexure mode composites with multiple resonant frequencies was also studied.