The Research On Pyroelectric Properties Of PVDF Thin Films

Poly(vinylidene fluoride)(PVDF) was widely used in sensors, transducers, biological sciences as functional materials because of its great piezoelectric, pyroelectric and ferroelectric properties. In this work, we introduced a method to prepare PVDF thin films with high β phrase by doping with GO(graphene oxide). The influence of(doping concentration of GO, annealing temperature, sorts of solvent, annealing environment) on β-phase and quality of samples was analyzed. The effects of GO on the crystallization of PVDF were examined by differential scanning calorimetry(DSC). We improved the electrical properties of PVDF thin films by polarization technology. The leakage, dielectric, ferroelectric and pyroelectric properties of PVDF thin films were measured.The test shows that the main crystal structure of GO doped PVDF thin films was β-phase and the grain size of thin films decreased from 15μm(pure PVDF) to 3μm(GO doing). The optimized annealing temperature of PVDF/GO thin films was identified to be 75 oC. It contributes to improve the β-phase and reduce the porosity in PVDF thin films by using vacuum annealing and mixed solvent of acetone and DMF.The DSC of PVDF and PVDF/GO shows that GO doping can effectively improve the crystallization rate of PVDF. The high doping concentration of GO can reduce the crystallinity of PVDF. When the crystallization temperature is 136 oC, the halftime of crystallization(t1/2) decreased from 1.17min(pure PVDF) to 0.73min(GO doing); the crystallization enthalpy decreased from 32.46 J/g(pure PVDF) to 24.2 J/g(GO doing).In the experiment, the leakage current of PVDF thin films is 1×10-9A, but the leakage current of PVDF/GO thin films(the concentration of GO was 1wt%) is 4.7×10-5A. At room temperature, the permittivity of PVDF thin film increased from 5.3 to 6.2 at 1 KHz.The results indicate that the breakdown voltage of PVDF thin films is reduced by doping with GO. The breakdown electric field decreased from 50MV/m(pure PVDF) to 18MV/m(GO doing). When the applied electric field is 24 MV/m, the remnant polarization of PVDF increased from 0 to 0.3μc/cm2. When the temperature is 50 oC, the pyroelectric signal of PVDF thin film after all can’t be detected, the pyroelectric coefficient of PVDF/GO thin film is 6.3×10-4C/(m2k). The voltage response of merit of PVDF/GO thin film is 5×10-9C.cm.J-1.The probe excellent value of PVDF/GO thin film is 4×10-8C.cm.J-1.The PVDF/GO thin film pyroelectric unit detector is studied. The frequency and power of radiation source is 1Hz and 13 mW, respectively. The output signal frequency of unit detector is 1Hz, the output voltage is 16.9mW. The pyroelectric current of unit detector is 0.169 pA.