Preparation And Performance Study Of PVDF-HFP/nano-ZnO Composite Film And Its Piezoelectric Senso

Polyvinylidene fluoride-hexafluoropropylene(PVDF-HFP)has the characteristics of thermoelectric,piezoelectric and high flexibility,but its piezoelectric properties are not high.Therefore,in order to obtain good piezoelectric properties on the basis of flexibility,nano-ceramic filler zinc oxide(ZnO)was used to obtain piezoelectric composites with the advantages of high voltage electric constant and high hardness,as well as good flexibility of polymers.However,the nano-fillers are easy to agglomerate.In this paper,the surface of nano-ZnO was modified by carbon tetrafluoride plasma,and the modified nano-ZnO was used to prepare PVDF-HFP/ZnO composite piezoelectric thin films.The effects of plasma modification on nano-ZnO and composite films were discussed,and the films were encapsulated to prepare piezoelectric sensors.The specific research contents are as follows:(1)The surface of nano-ZnO was modified by carbon tetrafluoride plasma,and the effects of plasma treatment on the surface morphology and internal structure of nanoZnO powder were analyzed.Through scanning electron microscope observation,Fourier transform infrared spectroscopy and X-ray diffraction characterization,it was found that plasma modification etched the surface morphology of nano-ZnO and became smooth,but did not affect the structure of the powder itself.(2)Using nano-ZnO as filler and mixing nano-ZnO solution with PVDF-HFP solution,pure PVDF-HFP film,PVDF-HFP/ZnO composite film and PVDF-HFP/modified ZnO composite film were prepared by scraping method.The surface morphology,crystalline phase and piezoelectric strain constants of the three kinds of films were studied by scanning electron microscope,Fourier transform infrared spectroscopy,X-ray diffraction and quasi-static D33 test.The results show that the plasma modified nano-ZnO is more uniformly dispersed in the composite film,and the content of β phase is 40.75%;the crystalline phase is mainly β phase.The average d33 value of the plasma modified composite piezoelectric film is ～ 29.2p C/N,which is 55%higher than that of the composite film made of untreated nano-ZnO(～ 18.8p C/N).(3)A flexible piezoelectric sensor was fabricated using copper foil as electrode and ethylene-vinyl acetate copolymer(EVA)film as substrate.The stability of the three kinds of piezoelectric sensors is tested by the self-made cyclic pressing system,and the vibration signal is tested by the shaking table test system.The results show that the fatigue damage of PVDF-HFP thin film sensor first occurs in the process of cyclic pressing,and the composite thin film sensor is more stable in the process of cyclic pressing,and the number of cycles can be more than 1500 times.In the process of100 Hz vibration testing,the output voltage range of PVDF-HFP/modified ZnO composite film sensor is higher than that of PVDF-HFP thin film sensor and PVDFHFP/ZnO composite film sensor under the amplitudes of 1.75 mm,1.8mm and 1.84 mm.