PVDF基高分子材料的挠曲电效应研究

Flexoelectricity has been intensively studied in recent years and is becoming a hot research topic in ferroelectric material area. This electromechanical coupling phenomenon is very important for the understanding of the unusual ferroelectric and dielectric properties in the materials of low dimension and nanoscale.Also, by exploiting flexoelectrcity, a type of new piezoelectric composite materials, flexoelectric piezoelectric composites, having excellent piezoelectric response can be designed. At present, flexoelectric study is mainly focused on inorganic materials, and for polymer materials, it is still in the early research stage. We found that, compared with ferroelectric ceramic-based flexoelectric piezoelectric composites, polymer-based composites could not only have comparable piezoelectric properties, but also the advantages of high mechanical reliability and low cost. In this study, PVDF, P(VDF-TrFE) and P(VDF-TrFE-CFE) polymers with controllable microstructure will be prepared by changing compositions or sample preparation conditions, and the flexoelectric response of these polymers will be further studied. Based on the experimental results, the correlation between the flexoelectric response of the polymers and various factors in materials, including crystal structure, crystallinity, and various polymer chain relaxation processes, will be studied and the intrinsic microscopic mechanisms that lead to the relationship will be further analyzed. With guidance of these results and analysis, polymers with high flexoelectric response will be further explored and polymer-based flexoelectric piezoelectric composites with piezoelectric properties higher than conventional piezoelectric polymers will be fabricated.

挠曲电效应研究近年来成为铁电材料研究领域的一个热点。这种机电耦合现象不仅对理解低维纳米材料的异常铁电和介电响应有着重要意义，而且可以用来设计出一类性能优异的新型压电复合材料：挠曲电压电复合材料。目前，挠曲电效应研究主要集中在无机材料，对高分子材料的挠曲电效应研究还处于起步阶段。我们发现，高分子基挠曲电压电复合材料不仅可以具有与铁电陶瓷基材料可比拟的压电性能，而且机械可靠性高，制备简单。本研究将针对PVDF、P(VDF-TrFE)和P(VDF-TrFE-CFE)铁电高分子材料，通过改变组分和制备工艺，制备出具有可控结构的高分子材料并研究这些材料的挠曲电效应，揭示聚合物组分、晶体结构、结晶度、高分子链运动等因素与挠曲电效应的关系规律及这些关系产生的微观机理，为进一步获得高挠曲电效应的高分子材料提供指导，并利用获得的材料制备出具有超过现有压电高分子材料压电性能的高分子基挠曲电压电复合材料。

挠曲电效应是一种梯度机电耦合效应，这种物理效应不仅于对理解纳米尺度的铁电材料中的一些物理现象有着重要意义，而且可以用来设计一些新型的机电器件。高分子材料具有柔性好，机械可靠性高，易加工等优点，可以用来设计和制备新型的挠曲电器件。目前人们对高分子材料的挠曲电效应仍缺乏深入的研究。PVDF基铁电聚合物具有比较高的介电系数，是一类具有较高挠曲电效应的材料。本课题主要针对PVDF基聚合物的挠曲电效应的产生机理和器件应用开展研究。我们制备了不同组分和晶体结构的PVDF基高分子材料，测量和对比了这些材料不同温度下的挠曲电系数，并进一步研究了影响PVDF基高分子材料挠曲电效应的因素和机理。我们发现PVDF基高分子的挠曲电响应与聚合物的结晶度和高分子链运动密切相关。我们的测量结果表明，PVDF基高分子材料的挠曲电系数基本在nC/m的量级，难以通过组分的调控较大幅度地提高它们的挠曲电系数。我们提出了复合材料方法，在PVDF中添加具有高挠曲电系数的铁电氧化物纳米纤维，将聚合物的挠曲电系数提高到10 nC/m以上。我们利用PVDF聚合物设计和制备了具有拱形结构和具有不对称结构的挠曲电压电复合材料，测量到了显著的表观压电响应（表观压电系数约3.5 pC/N）。本课题的研究对深入理解高分子材料的挠曲电效应的产生机理以及PVDF基聚合物在挠曲电器件中应用具有重要意义。