高度取向聚偏氟乙烯及其共混/共聚超薄膜的结构与铁电性能关系研究

Ferroelectric polymer memories targeting next generation transparent and flexible electronics are experiencing unprecedented levels of research activity. Poly(vinylidene fluoride)(PVDF) is one of the most important ferroelectric polymer. Controlling the structures of PVDF thin film and optimize the properties of PVDF-based memories devices is a very hot topic..In this project, PVDF, PVDF/poly(methylmethacrylate) (PMMA) blend films and PVDF copolymer are adopted. The PVDF ultrathin film with high orientation degree is prepared by using melt-drawn technique and epitaxial crystallization method. The crystal orientation structure and morphology of oriented PVDF are characterized by using polarized optical and transmission electric microscopy, atomic force microscopy, infrared spectroscopy and X-ray. In addition, the local ferroelectric properties are obtained by piezoresponse force microscopy. The aim of this project is to: (1) indentify the preparing method of PVDF ultra thin film with high orientation degree and high amount of ferroelectric phase; (2) control the orientation structure and morphology of PVDF ultrathin film by changing force, epitaxial substrate, and thermal treatment method; (3) get the key factors which affect the ferroelectric phase and orientation; (4) build the relationship between ferroelectric phase structure and properties in oriented thin film. Through the research, the useful theory guidance can be provided for the PVDF-based non-volatile memory devices studies.

随着人们对记忆器件柔韧性，存储密度等要求的提高，对聚合物基铁电超薄膜结构，性能的调控及存储器件的设计成为聚合物铁电材料的研究热点之一。为提高PVDF超薄膜的铁电性能，本项目拟选择PVDF、 PVDF/PMMA的共混物、PVDF的共聚物，采用熔体拉伸及取向基底附生的方法，将其制备成具有高度取向结晶结构的PVDF超薄膜。将用偏光及电子显微镜，红外及X衍射等分析方法表征超薄膜中晶体的取向结构及形态。同时借助压电响应显微镜对所制得的取向PVDF薄膜的电畴结构分布及极化行为进行研究。确定高度取向且具有高铁电相聚偏氟乙烯及其共混或共聚超薄膜的制备方法；通过改变拉伸力，取向基底，热处理条件等实现对PVDF超薄膜的二维结晶，取向结构及形态的调控；确定影响PVDF铁电相形成及取向的关键因素；建立取向超薄膜中铁电相结构形态-极化性能的相互对应关系。为PVDF基的非易失记忆器件的研发提供行之有效的理论指导。

随着人们对记忆器件柔韧性，存储密度等要求的提高，对聚合物基铁电超薄膜结构，性能的调控及存储器件的设计成为聚合物铁电材料的研究热点之一。为提高聚偏氟乙烯(PVDF)超薄膜的铁电性能，本项目首先利用界面相互作用力调控了PVDF及其共聚物相对于基底的取向结构，随后又利用熔体拉伸的方法制备了PVDF取向超薄膜，最后又利用取向的PVDF薄膜作为基底通过附生结晶的方式控制了共聚物的取向结构。在精准控制PVDF基聚合物晶体结构的基础了，又进一步对其压电和铁电性能进行了研究。最终确定了高度取向且具有高铁电相聚偏氟乙烯及其共混或共聚超薄膜的制备方法；通过改变拉伸速率，取向基底，热处理条件等实现了对PVDF超薄膜的结晶，取向结构及形态的调控；明确了影响PVDF铁电相形成及取向的关键因素；建立了超薄膜中关键结构因素对其压电、铁电性能的影响规律。

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