氢化法P(VDF-TrFE)结晶、服役中相变及其铁电、压电和介电性能调控

Poly(vinylidene fluoride) (PVDF) and its copolymer poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) with high dielectric property and electric-mechanical efficiency were confirmed a wide application prospect in the various electronic device applications such as energy conversion and sensor areas. Compared to the pure PVDF films with complicated processing technology and the expensive direct-copolymerized P(VDF-TrFE), the new hydrogenated P(VDF-TrFE) exhibits favorable characters such as low price and facile film fabrication. However, because of the absence of related corresponding phase transition and dielectric theories, it is difficult to understand the relation of condensed state and electric properties of this novel copolymer. In this project, hydrogenated P(VDF-TrFE) with various composition will be synthesized firstly by atom transfer radical chains transfer (ATRCT) and controllable elimination reactions. Secondly, the standard characterization method by combining WAXD and DSC fitting techniques will be developed to precisely evaluate the crystalline phase morphology. Furthermore, based on the investigation of how the composition of polymers such as TrFE contents, fabricated conditions, and service circumstance influence the crystalline phase (α, β, and γ) transition and ferroelectric- paraelectric (F-P) phase transition, the corresponding phase diagram for hydrogenated P(VDF-TrFE) will be established. Finally, by carefully investigating the dielectric properties under different measurement frequencies, temperatures and electric fields, and combining the composition and structure, crystalline phase transition and F-P transition, the comprehensive ferroelectric, piezoelectric, and dielectric regulation mechanism will be illuminated, which may provide a reliable theoretical direction for the structure design of hydrogenated P(VDF-TrFE) aim at various applications.

高压电常数和机电转换效率的PVDF和P(VDF-TrFE)铁电压电薄膜在能量转换和信息存储等领域具有极重要的应用前景。同目前PVDF膜复杂成型工艺和直接共聚P(VDF-TrFE)高成本相比，新发现的氢化法P(VDF-TrFE)具有易合成和极高的性价比优势。针对目前氢化法P(VDF-TrFE)在相变、电性能等理论方面的认识不足，本项目拟采用可控自由基链转移技术制备出各化学组成的氢化法P(VDF-TrFE)；然后利用DSC分峰和WAXD技术建立氢化法P(VDF-TrFE)结晶研究的新方法，准确表征TrFE比例和服役条件对其结晶的影响；进而在深入探究P(VDF-TrFE)膜F-P相变行为基础上，绘出综合相图；最后通过关联P(VDF-TrFE)在强度、频率差异电场和等静压下服役中的相变行为，揭示其相变行为和铁电、压电和介电特性调控机制，为此类聚合物的构象设计及其在相关领域中的应用奠定基础。

分别用原子自由基链转移方式和硅自由基串联反应氢化P(VDF-CTFE)，得到了TrFE含量为6mol%-50mol%的8种氢化P(VDF-TrFE)；利用XRD、DSC分峰技术结合FTIR解释了TrFE含量和P(VDF-TrFE)铁电和压电性能的构效关系。发现TrFE引入可提升P(VDF-TrFE)分子链的内旋转能垒，TrFE为80mol%时P(VDF-TrFE)具有高的铁电性能（饱和和剩余极化强度分别为15.1μC∙cm-2和11.4μC∙cm-2），高电场极化后压电常数为-25pC/N；.研究了TrFE为6mol%-50mol%的α、β和γ混合晶相氢化P(VDF-TrFE)的F-P相变行为，解释了高电场服役条件下P(VDF-TrFE)膜中α和γ晶相向β的转化机制和高等静压力对晶畴翻转的抑制机理。发现随TrFE摩尔含量的增加后，聚合物单个结晶区尺寸减小，电畴反转位阻变小，非极性或弱极性α、和γ晶翻转转化成β晶相的电场阈值降低。在此基础上，绘制了氢化法P(VDF-TrFE)综合相图，发现P(VDF-TrFE)80/20mol%各项电性能优于其他成分聚合物。.在明确P(VDF-TrFE)分子结构、结晶和压电铁电性能构效关系基础上，全面测试了P(VDF-TrFE)80/20mol%各项物理性能。发现其作为声发射传感器时在20～40 kHz超声段响应灵敏，14 mV信号频率峰尖锐；作为脉冲压力传感器且信号响应线性较好，500mm/min速度的10Pa冲击力作用时，输出电压为6.8V，响应时间为2ms。.综上，本项目阐明了氢化法P(VDF-TrFE)分子构象、制备条件以及高电压等服役环境对其结晶结构和晶相转变的影响机理，解释了其服役过程中电畴翻转、抑制条件、F-P相变机理与铁电、压电性能调控机制；本项目的应用研究为P(VDF-TrFE)服务于国防和民用传感器领域奠定了良好的基础。