单轴拉伸对聚偏二氟乙烯薄膜压电响应性能的影响

Effect of Uniaxial Tension on Piezoelectric Response of PVDF Film

采用溶液涂覆成膜工艺制备聚偏二氟乙烯(PVDF)薄膜,对其进行单轴拉伸制得不同拉伸比(R=3,5,7)的PVDF薄膜.研究了不同拉伸比对薄膜化学结构、结晶行为、铁电性能及压电响应性能的影响,实现了对PVDF结晶相的本征压电响应性能的增强.单轴拉伸使PVDF结晶度提高,同时促使其结晶相由α相向β相转变;拉伸比越大,极性β相相对含量越高,当拉伸比为7时,薄膜β相的相对含量最高达到85.12%,此时薄膜的电输出性能最佳:外加电场为200 MV/m时,其剩余极化强度为2.69μC/cm^2;应变为5%时,其平均闭路电流密度为58.92 nA/cm^2,平均开路电压为89.70 mV.

In order to prepare organic piezoelectric materials with good piezoelectric properties and enhance the intrinsic piezoelectric properties of the poly(vinylidene fluoride)(PVDF)crystal phase,a solution coating filmforming process was adopted to prepare PVDF films.The films with different stretch ratios(R=3,5,7)were made by uniaxial stretch process.The morphology and structure of the films were investigated by scanning electron microscopy(SEM),transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),differential scanning calorimetry(DSC).Gold electrode is sprayed on the surface of the film and then the film is subjected to highvoltage electric field polarization treatment.Connect the films to the sampling multimeter to further study the piezoelectric properties of the films.It shows that uniaxial stretch can increase the crystallinity of PVDF and promote the transformation ofαphase intoβphase.During the stretch process,the molecular segments of PVDF are highly oriented to form theβphase of the all-trans conformational structure.The larger the stretch ratio,the higher the crystallinity of PVDF and the higher the relative content of the polarβphase.When the stretch ratio is 7,the relative content ofβphase increases to 85.12%,which is 1.5 times higher than that of the unstretched film.Since the intrinsic piezoelectric properties of PVDF are controlled by its crystallineβphase content,the larger the stretch ratio,the better the ferroelectric and piezoelectric properties of the film.The film exhibits the best electrical properties when it is stretched 7 times:When the applied electric field is 200 MV/m,the residual polarization intensity reaches 2.69μC/cm2.When the strain is 5%,the average output current density is 58.92 nA/cm2,and the average output voltage is 89.70 mV.In this study,the single-axis stretched PVDF film has a high voltage sensing sensitivity,and a PVDF film in a small area size(22 mm×4 mm)can provide an output voltage as high as 89.70 mV.Therefore,the material can be used to produce ultra-thin,lightweight portable electronic devices in ideal shape,and is expected to be used as a flexible touchable sensor to obtain biomechanical energy from the human body for health monitoring.