Study On Preparation And Performance Of P(VDF-TrFE)-based Flexible Ferroelectric Composite Film

The inherent rigidity and brittleness of traditional functional materials limits the application for the field of flexible wearable devices.General flexible materials have poor performance,which cannot meet the functional requirements of flexible devices.Therefore,it is of great significance of flexible electronics to develop a flexible material,which has good flexibility,versatility and machinability.The polyvinylidene fluoride-trifluoroethylene(P(VDF-Tr FE))possesses many intrinsic properties such as ferroelectricity and piezoelectricity.Moreover,it also has the advantages of extraordinary flexibility and easy processing,which is bound to play an important role in the field of flexible wearable devices.However,the performance of polymers is much lower than traditional functional materials.Therefore,this dissertation effectively improved the ferroelectricity,piezoelectricity and dielectric properties of the P(VDF-Tr FE)ferroelectric film from the aspects of optimizing the preparation and composite modification.In this dissertation,the solution casting method was mainly used to prepare P(VDF-Tr FE)ferroelectric films.First the best preparation process was explored.It was found that the use of a higher polarity DMF solvent and the treatment temperature of 100 ^oC can prepare P(VDF-Tr FE)films with good film quality.The dielectric constant of 1000 Hz at room temperature was 12.58,and the maximum polarization and residual polarization obtained were 8.30?C cm^-2and 7.18?C cm^-2 under the 140MV m^-1,respectively,showing good dielectric and ferroelectric properties.P(VDF-Tr FE)ferroelectric thin films with different molar ratios were prepared based on the optimal preparation conditions.The DSC test showed that the Curie temperature shifted to low temperature and the melting temperature to high temperature with the Tr FE from 20 mol%to 45 mol%.Besides,the dielectric test showed that the P(VDF-Tr FE)55/45 mol%film had the largest relative dielectric constant of 15.73 at 1 k Hz.However,the ferroelectric and the dielectric test found that a small amount of Tr FE mol%can enhance the ferroelectricity and piezoelectricity.The P(VDF-Tr FE)80/20 mol%film exhibited better ferroelectricity and piezoelectricity.Prepared into a flexible piezoelectric sensor,the film sensor showed that the output voltage tested by finger pressing was about 1.5 V,and it also showed good piezoelectric response from different pressure tests.Two kinds of Bi Fe O₃ nanoparticles,square and spherical,were prepared by hydrothermal method and sol-gel method.It was found that the composite film with spherical nanoparticles showed better ferroelectricity.Bi Fe O₃ nanoparticles modified with polydopamine(PDA)successfully achieved good dispersion in the polymer.The composite film of 5 wt.%Bi Fe O₃@PDA obtained the maximum saturation polarization of 8.75?C cm^-2 and the residual polarization of 6.88?C cm^-2 under the100 MV m^-1 test.The piezoelectric coefficient of the composite film was as high as18.20 p C N^-1.At the same time,the 5 wt.%composite film exhibited a better piezoelectric response.The output voltage was about 1 V by a finger press,and it can stably output a voltage of 0.8 V under a constant pressure of 8 N.Used as an energy harvester,it also successfully lit up the red LED.In this dissertation,P(VDF-Tr FE)ferroelectric film and Bi Fe O₃@PDA composite film were prepared by casting method.The preparation method was simple,high-efficiency and low-cost.The ferroelectric thin film had good electrical properties,which contributes to realize the large-scale industrial production of flexible film devices.This provided a reference for P(VDF-Tr FE)composite film material to realize stress sensor and self-powering in flexible wearable devices.