聚偏氟乙烯及其共聚物的极化取向控制与性质提高

Poly(vinylidene fluoride) (PVDF) and its copolymers with trifluoroethylene (P(VDF-TrFE)) have received considerable attention due to their unique combined properties of ferroelectricity, piezoelectricity, pyroelectricity, and flexibility, low cost, ease of production. Much progress has been made in understanding their structures and macroscopic properties in recent years. In order to integrate PVDF and P(VDF-TrFE) in all-organic low-power electronic devices, it is desirable to decrease its switching voltage while improving physical properties. Lower switching voltages can be intuitively attained by decreasing the film thickness. This was however reported to lead to deteriorated ferroelectric properties.The objective of the present proposal is to enhance the understanding of structure, morphology and ferro/piezoelectric properties of PVDF and P(VDF-TrFE) (ultra-)thin films, and to control the molecular and lamellar orientation. This will be achieved through controlling the crystallization in confined geometry which aims to improve the orientation order and through investigating the polarization switching in both macroscopic and microscopic scale. Ultimately, arrays of PVDF and P(VDF-TrFE) nanostructures with highly oriented internal structures and improved ferroelectric or piezoelectric properties will be fabricated. If success, this project is not only important for understanding the structure-property relationship of functional polymers, but also important for developing the strategies of obtaining highly ordered polymer materials.

聚偏氟乙烯及其与三氟乙烯的共聚物由于具有优异的铁电、压电和热电性而在信息存储、压力传感、热电传感等众多领域拥有广阔的应用前景。尽管近年来在材料的凝聚态结构和宏观性质研究方面取得了很大进步，但调控它们的分子和片晶择优取向和构筑高度有序微纳米结构阵列对于提高材料和器件的性能极其重要。本项目拟在深入研究聚偏氟乙烯及其与三氟乙烯共聚物的薄膜或超薄膜在一维空间受限环境和表面相互作用下的结构形态演变规律的基础上，利用二维空间受限环境和界面相互作用协同效应，构筑高度取向有序的微纳米结构阵列。通过深入研究高度取向有序的聚偏氟乙烯及其共聚物薄膜、超薄膜和微纳米结构阵列的极化反转过程以及结构-性质关系，实现提高和优化以聚偏氟乙烯及其共聚物为主要构建单元的材料和器件性能的目的。这不但可以进一步加深对功能高分子材料结构-性质关系的认识，而且发展了调控高分子材料的凝聚态结构方法，同时奠定了制备高性能器件的坚实基础。

聚偏氟乙烯及其共聚物由于具有优良的铁电/压电/热释电性能而在近些年备受关注，具有广阔的应用前景。聚偏氟乙烯及其共聚物薄膜（或超薄膜）中beta相片晶含量和片晶取向是决定其物理性能的重要因素。在本项目中，我们主要利用离子-偶极和氢键界面相互作用调控了旋涂法制备的聚偏氟乙烯薄膜中beta相的形成，beta相的含量大于80%；综合利用纳米压印过程中模板的二维限域空间环境和界面相互作用构筑了beta相片晶取向高度有序的微纳米结构阵列，提高和优化了聚偏氟乙烯及其共聚物薄膜的铁电性能；进而，利用beta相片晶取向高度有序的微纳米结构阵列成功地制备了具有低电压读写特性的铁电信息存储器，阐释了铁电高分子聚集态结构的多层次性对其极化偶极在电场作用下反转过程的影响规律。本项目的研究成果为进一步研究和发展柔性铁电/压电器件奠定了基础。