聚偏氟乙烯α相向γ′相的相转变机理研究

聚偏氟乙烯（PVDF）是一种多晶型聚合物，其压电、铁电性能强烈依赖于PVDF的晶型。PVDF的α相是非极性相，不具备压电、铁电性能。与γ球晶接触的α球晶在高温下退火转变为具有铁电性能的γ′相。二者的相转变研究一直停留在微米尺度的认知上面，相转变机理尚未有深入系统的研究。本项目拟结合温度场、剪切外力场等技术制备以不同方式相互接触的α相/γ相，如球晶/球晶、横晶/横晶接触等；用原子力显微镜、微束X射线、纳米红外、显微红外/拉曼等技术原位追踪α相向γ′相的相转变过程中分子链构象/构型、晶体结构/形态等多层次结构的演变过程；明确薄膜厚度、晶体取向、温度、α/γ相接触方式等对相转变的影响规律，从分子水平揭示α相向γ′相的相转变机理，并进一步研究γ′相的微观、宏观压电、铁电性能。

Poly(vinylidene fluoride)(PVDF) is a kind of polymorphic polymer.The piezoelectric and ferroelectric properties highly depend on the crystal phase. The α phase of PVDF is nonpolar phase which does not show piezoelectric and ferroelectric properties. The α phase which is contacting with γ phase is able to transit to γ′ phase when annealing at high temperature for long time. Previous studies on the transition of α to γ′ are mainly limited at the micrometer scale and the transition mechanism is not clear. In this project, the α phase and γ phase will be prepared which are contacting with each other in different way by employing different methods. The samples with α spherulites contacting with γ spherulites will be prepared through the melt-recrystallization of static melt. While the samples with α transcrystalline phase contacting with γ transcrystalline phase will be also prepared through a shear equipment. The phase transition processes are characterized by using Atomic Force Microscopy, Micro-X-ray technology, Nano-IR, micro-Infrared and Raman spectroscopy technologies. The structure evolution including molecular conformation, crystal structures and morphology etc. is monitored accordingly. In addition, the piezoelectric and ferroelectric properties are measured. The aim of this project is to: (1) identify the effect of film thickness, crystal orientation, thermal treatment temperature, contacting way of α and γ phase on the phase transition behavior; (2) clarify the phase transition mechanism of α phase to γ′ phase.