聚偏氟乙烯薄膜挠曲电效应的实验研究

Experimental investigation of flexoelectric effect in polymer polyvinylidene fluoride thin films

非均匀应变如应变梯度能够局部破坏晶体的反演对称,在介电材料中产生极化现象,这称为挠曲电效应。挠曲电效应是一种普遍存在的力电耦合现象,且与应变梯度相耦合,在微纳米尺度不可忽略。研究者已经测量了一系列铁电陶瓷材料的挠曲电系数,然而关于聚合物材料挠曲电效应的实验研究相对有限。本文基于四点弯曲实验测量了聚偏氟乙烯材料的挠曲电系数,避免了以往悬臂梁弯曲实验中应变梯度分布不均匀引起的误差,在1~4Hz加载频率范围测量了两种不同厚度聚偏氟乙烯薄膜的挠曲电系数;分析了准静态情况下聚偏氟乙烯材料挠曲电系数的稳定性,并验证了挠曲电系数的尺寸效应。本文工作提供了测量聚偏氟乙烯薄膜挠曲电系数的实验方法,并为基于挠曲电效应的传感、驱动器件设计提供了工程数据。

Nonuniform deformation such as strain gradient can locally break the inversion symmetry of crystalline,and will result in electric polarization in all solid dielectrics,which can be termed as the flexoelectric effect.This is a universal electromechanical coupling phenomenon that exists in all dielectric materials.It is usually coupled with the strain gradient,and therefore cannot be ignored for micro/nano-materials.The flexoelectric coefficients in a series of ferroelectric ceramics have been measured in experiments,but the investigation of the flexoelectric effect in polymers is still limited.In this work,the flexoelectric coefficient for polymer polyvinylidene fluoride thin films is experimentally measured by utilizing the four-point bending test,which can reduce the overestimate or underestimate of the flexoelectric effect in materials appearing in previous cantilever-based measurements.Based on the four-point bend test,the flexoelectric coefficient of polymer polyvinylidene fluoride thin films with two different thicknesses are experimentally measured at the load frequency of 1〜4Hz.The stability of the flexoelectric coefficient varying with the load frequency is also discussed.Moreover,in this work we try to verify the size effect corresponding to the flexoelectric effect.The current work provides the four-point bending experiment technique for measuring flexoelectric coefficient of thin films,and it is also helpful in designing flexo-based applications,such as sensors and actuators.