| The traditional piezoelectric materials are mainly piezoelectric crystal and piezoelectric ceramics.The piezoelectric properties of these materials are good,but in application,they are often limited by their brittle and high-density characteristics,which will lead to the problem of difficult to process and fracture in application.In recent years,piezoelectric materials have been developed continuously.Polymer piezoelectric materials such as PVDF have been applied in piezoelectric field because of its light weight and good formability.However,due to its low d33 and high voltage when polarization is needed,more research focus is on piezoelectric composite materials which consider the advantages of piezoelectric ceramics and piezoelectric polymers.Especially in the field of underwater acoustic transducer,compact piezoelectric ceramics are limited in application due to their poor dexterity.It is urgent to develop a new composite material which can match the acoustic impedance of water.The aerogel material with nano network skeleton will benefit the development of new piezoelectric composites due to its small density,low acoustic impedance,and the sensitivity of piezoelectric ceramics to interlayer sliding.In this study,PZT/SiO2-Al2O3 aerogel/PVDF composite films were prepared by combining piezoelectric ceramic particles and aerogels in situ and then compounding with piezoelectric polymers.The composite film not only retains the soft properties of piezoelectric polymers,but also makes good use of piezoceramic resistance to high temperature and enhances the piezoelectric sensitivity of composite thin films through the chimeric of aerogel nano network skeleton with PZT.It has good prospects in the applications of underwater acoustic transducers and sensors,including actuators.In this study,the preparation conditions of PZT and SiO2-A12O3 were investigated.The PZT gel was prepared by the sol-gel method.The relationship between the crystalline form,microstructures,and preparation process of PZT was studied by investigating the effects of different drying methods and calcination temperatures on PZT ceramics.The optimum technological condition was determined as CO2 supercritical drying.Pb(Zr0.52Ti0.48)O3 ceramics with coarse surface structure and single perovskite structure were obtained by annealing at 600℃.The gel rapid gelation process was studied by investigating the influence of gel temperature on gel time.It is found that the gel time is shortened greatly when the temperature is above 70℃,which is beneficial to the composite process of composite aerogels.PZT/SiO2-Al2O3 composite aerogel was successfully prepared by an in-situ rapid composite process.By investigating the effect of PZT addition on the structure and pore structure of the composite aerogel,it was found that with the increase of PZT content,PZT in the composite aerogel dispersed uniformly,and the specific surface area of the composite aerogel increased gradually,resulting in a composite specific surface area of 711m2/g.Secondly,PZT/SiO2-Al2O3 aerogel/PVDF composite films were prepared by two fast and efficient solution compounding methods:powder method and composite aerogel method.The relationship between the preparation process and the microstructures of the materials was investigated by investigating the effects of the process conditions such as the amount of aerogel added,the amount of PZT added,the thickness of the film,the type of aerogel and the preparation method on the piezoelectric properties.The piezoelectric mechanism of PZT/SiO2-Al2O3 aerogel/PVDF composite film was investigated by means of SEM,EDS,infrared,thermal conductivity,piezoelectric coefficient,and dielectric constant measurements.The influence of the microstructure on the piezoelectric performance was analyzed,and the relationship between the preparation process,structure and performance was discussed.It is found that the thermal insulation performance of the composite film is improved,and the increase of PZT and aerogel content is beneficial to the increase of the piezoelectric coefficient of the piezoelectric composite film.The effect of SiO2-Al2O3 aerogel on piezoelectric coefficient is better than that of SiO2 aerogel.When the content of PZT in composite film prepared by composite aerogel method is 45 wt.%,and the thickness of film is 25μm,d33 can reach 15pC/N.With the increase of PZT content,the proportion of aerogel decreases relatively,and the dielectric constant of the composite film decreases.The dielectric loss of the composite film does not differ much from that of the PVDF film.Thirdly,to enhance the polarization effect of PVDF-based composite films,doping CNTs are used to try to enhance the conductivity of the composite films.By investigating the piezoelectric coefficient of the composite films,the influence of the content of CNTs on the polarization effect of the composite films is explored.The results show that the piezoelectric coefficient of the composite film has a peak value with the increase of CNTs content in the powder method,and the composite film has the best polarization effect when the CNTs content is 2 wt.%.However,the piezoelectric composite films prepared by the composite aerogel method failed to show the direct connection with the amount of CNTs doping,which may be due to the formation of conductive paths in the aerogel skeleton.Therefore,future research can be considered to replace the polymer PVDF by polymers with better conductivity(such as PI)or reduce the doping amount of CNTs. |
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