PVDF薄膜单轴拉伸及交流极化特性研究

Study on the uniaxial orientation behaviors and polarization properties of PVDF films

研究制备压电聚偏二氟乙烯(PVDF)薄膜的两个关键步骤——拉伸和极化。在单轴拉伸中,在不同拉伸倍率下(R=2,3,4,5)晶区发生到的相变,拉伸前后薄膜中相含量相差较大,随着拉伸比的增大含量的增加速率变小,在R=5时达到最大值75%。在交流热极化中,测量在不同极化波形(三角波和正弦波)下,流经PVDF薄膜中的电流,使用数值补偿法消除电导电流和线性感应电容电流的影响,得到薄膜极化电流;在正弦电场下,研究不同频率对薄膜极化性能的影响,在低频(f=0.1 Hz)下更多偶极子发生翻转且所得到的电流曲线受电导和电容效应影响较小;拟合得出剩余极化强度与外加电场之间的非线性关系。在相同的低频正弦极化电场下,对薄膜样品的压电性进行测试,分别测量其压电系数d33值,其A类不确定度约为7%,说明采用低频交流极化的方法所得到的压电薄膜具有较好的一致性和重复性。

Two vital steps in the fabrication of piezoelectric polyvinylidene fluoride(PVDF)films are stretching and polarization.In the uniaxial stretching process,the stretching ratio(R=2,3,4,5)largely affects the phase transition in PVDF films.As the stretching ratio rises,the increases of phase occupation and reaches a maximum relative content of 75%at a stretch ration of 5.In the polarization,the electric current through the PVDF film under the two different electric waveforms(triangle and sine)is measured.The numerical compensation method is used to eliminate the influence of conductive and capacitive current.Under sinusoidal electric field,the effects of polarization frequencies on the dielectric properties of the films are studied.At a low frequency f=0.1 Hz,more dipoles are flipped and the measured current curve is less affected by conductance and capacitance.The non-linear relationship between the residual polarization and the electric field is obtained by fitting.Under the same poling condition,the piezoelectricity of the seven samples are evaluated by measuring the piezoelectric constant d33.A-type uncertainty is about 7%,indicating that the low frequency alternating electric field can be utilized to produce piezoelectric PVDF films with better consistency and repeatability.