Enhancing Piezoelectric Response Of P(VDF-TrFE)Films By Surface Relief Structures

Self-powered piezoelectric sensors have attracted considerable attentions in recent years owing to their great potential applications in healthcare,electronic skin and motion monitoring.Among piezoelectric materials,polyvinylidene fluoride(PVDF)and its copolymers are the most promising candidate materials for self-powered flexible piezoelectric sensors due to their unique piezoelectric properties,high flexibility,machinability and chemical stability.However,the piezoelectric response of PVDF-based devices in terms of mechanical-to-electrical energy conversion capacity is not comparable to their inorganic ceramic counterparts due to their relatively low piezoelectric coefficient.The absolute d33 value of PVDF is about-30 pC N-1,which is only about 1/20?1/8 that of the commonly used lead zirconate titanate(PZT).In order to improve the piezoelectric performance of PVDF-based flexible piezoelectric sensors,researchers have proposed a number of improved methods,the main means of which are to improve the piezoelectric constant d33 through adjusting the crystallinity,the ?-phase content and the molecular chain orientation of PVDF and its copolymer films.In this thesis,we propose a new method to enhance the piezoelectric properties of polyvinylidene fluoride-trifluoroethylene(P(VDF-TrFE))films,by using solvent-assisted micro-molding technology to build a well-defined surface relief structures on the surface of P(VDF-TrFE)film to improve its piezoelectric performance.Compared the electrical performance test results of P(VDF-TrFE)films with those of P(VDF-TrFE)films with different periodic surface relief structures,we found that the introduction of relief structures onto P(VDF-TrFE)films could increase the output voltage of the devices by 2.3?4.5 times and the sensitivity by 2.9?4.6 times under the same test conditions.In addition,the output voltage and sensitivity of P(VDF-TrFE)film piezoelectric devices with different periodic surface relief structures increased first and then decreased.Furthermore,we use the finite element analysis(FEA)to study systematically the influence of the characteristic size of the surface relief structures on the piezoelectric properties of P(VDF-TrFE)films.Based on the experimental and theoretical calculation results,it is concluded that the main factor affecting the piezoelectric output of the piezoelectric devices is the strain enhancement of the piezoelectric film caused by the confinement effect,and the coupling effect between the stripes and the bottom residual layer can play a certain role in regulating the output voltage of the device.These findings will provide a new idea for improving the performance of piezoelectric devices through the design of accurate surface topography engineering.