Preparation And Properties Study Of Flexible Piezoelectric Sensor Based On PVDF-TrFE/ZnO Composite Film

With the vigorous development of information technology and emerging electronic industry,wearable equipments have become an important position of scientific research and industrial transformation in the world.Compared with piezoelectric ceramics,polyvinylidene fluoride（PVDF）and its copolymers have the advantages of high sensitivity,easy processing,good flexibility and low density.However,the piezoelectricβphase of conventional PVDF films is greatly affected by the preparation process and has poor controllability.The copolymer polyvinylidene fluoride-trifluoroethylene（PVDF-TrFE）with high content ofβphase and high flexibility can be easily obtained due to its unique structure,which makes it become one of the ideal materials for active layer of the device.In this paper,by adding nano-zinc oxide（ZnO）into PVDF-TrFE to improve theβphase content of the film,a flexible piezoelectric sensor with excellent performance was fabricated.Firstly,nano-ZnO was modified with n-propylamine（PA）and 1H,1H,2H,2H-perfluorooctyl trimethoxysilane（PFOES）to solve the dispersion of ZnO in PVDF-TrFE.Secondly,composite films with higherβphase content were obtained by optimizing the spin-coating process parameters.In addition,nano-ZnO quantum dots with smaller particle size than purchased nano-ZnO were prepared by supersonic alcohol-alkali method and compared with PVDF-TrFE was compounded to investigate the effect of reaction conditions on the piezoelectric properties of PVDF-TrFE/ZnO quantum dot composite films by ultrasonic alkali-alcohol method.Finally,the effect of adding buffer layer polyvinylpyrrolidone（PVP）into the sensor on the piezoelectric output was discussed.Through the above research,the conclusions are as follows:（1）The addition of PA and PFOES at the same time facilitates the dispersion of nano-ZnO in PVDF-TrFE,increases the formation of piezoelectricβphase and the specific surface area of the film,so that the piezoelectric strain constant of the film is higher（34.7±2.4pC/N）.The piezoelectric output of the prepared piezoelectric sensor（2.65±0.10 V）is the largest.（2）Among the spin-coating process parameters for preparing PVDF-TrFE/ZnO active layer,when the spin-coating speed is 2000 r/min and the number of spin-coating is 3,the content ofβphase is the highest,the piezoelectric strain constant（34.7±2.4 pC/N）of the composite film is the largest.The piezoelectric output of the corresponding piezoelectric sensor is 2.65±0.10 V.（3）ZnO quantum dots were prepared by ultrasonic alkali-alcohol method.The average particle size of the ZnO quantum dots was smaller when LiOH was used as alkali source,ultrasonic time was 60 min,and the ratio of Zn²⁺:OH^-was 1:2.The piezoelectric strain constant d₃₃ of the composite film was 40.8±0.3 pC/N.The piezoelectric output value of the sensor fabricated with the composite film as active layer was 3.23±0.09 V,which was smaller than that of the sensor fabricated with PVDF-TrFE/nano ZnO.The output value of the sensor with composite film as active layer is increased by 21.9%.（4）Through the drop ball experiment,it can be concluded that the piezoelectric output value（1.85±0.03 V）of the sensor without PVP buffer layer is more stable than that of the sensor without PVP buffer layer（1.82±0.13 V）,because the contact area between the active layer and the electrode is increased by the PVP buffer layer,which is more conducive to the conduction of charge between the active layer and the electrode.Finally,Izod actuator is used to test the stability of the sensor with PVP buffer layer.After 1000 cycles,the output voltage of the flexible piezoelectric sensor is kept at 2.40 V.It can be concluded that the flexible piezoelectric sensor prepared in this experiment has high mechanical fatigue resistance.