Studies on the Formatio Mechamisms and Functionality Properties of Single Crystalline Flims of Ferroelectic Polymers

我们以前发现偏氟乙烯和三氟乙烯的铁电共聚物P(VDF/TrFE)结晶成高度结晶的、高度双向取向的薄膜，我们称之为单晶(SC)薄膜。Sc膜既不存在非晶相，也不存在片状晶体，是研究聚合物晶体各向异性的最佳材料。在这个研究项目中，我们研究了(I)Sc薄膜的结构及其形成机制，(Ii)居里温度以上异常介电行为的起源，从顺电相中分子链运动的角度，(Iii)压电性能及其在剪切波超声换能器中的应用，以及(Iv)电光性能。(1)正交相的Sc膜为孪晶，其c轴取向平行于拉伸轴，b轴(极轴)取向偏离薄膜法线300。在顺电p…中更容易形成六方单晶，六方[100]轴垂直于薄膜表面。晶轴择优取向在顺电(六方)相中发展，这是由于六方相中(100)面的自由表面能最低所致。(2)X射线衍射和介电弛豫测量揭示了顺电相中分子链的运动：TGTG构象的每个链分子在六方晶体中独立于相邻的链分子发生翻转运动和旋转运动，是具有液晶特性的晶体。基于这些信息，我们建立了一个新的概念来解释顺电相中出现的反常介电性质。(3)Sc膜具有非常有效的剪切压电性。我们研制了用于横向超声波的换能器，该换能器已被证明在工业材料的非无损检测中是实用的。(4)测量了薄膜的电光性能(Pockels效应)。除上述结果外，我们还对(A)P(VDF/TrFE)/PMMA共混物、(B)高压结晶P(VDF/TrFE)/PVDF和(C)高压结晶聚乙烯取向膜的结构和性能进行了研究。较少

We previously found that ferroelectric copolymer of vinylidene fluoride and trifluoroethylene, P (VDF/TrFE), crystallizes into a highly crystallized, and highly double-oriented film, which we call a single crystalline (SC) film. The SC film is best material to investigate anisotropic properties of polymer crystals, because it do not have amorphous phase nor lamellar crystals. In this research project we have studied (i) the structure of SC film and its formation mechanisms, (ii) the origin of anormalous dielectric behavior apperaring above the Curie temperature, from the standpoint of molecular chain motions in the paraelectric phase, (iii) piezoelectric properties and its application to shear wave ultrasonic transducers, and (iv) electro-optical properties.The results obtained are as follows. (1) The SC film in the orthormbic phase is a twin crystal, whose c-axis orients parallel to the stretching axis, and the b-axis (polar axis) orients 300 off the film normal. In the paraelectric p … More hase it becomes a hexagonal single crystal, the hexagonal [100] axis being normal to the film surface. The preferential orientation of the crystal axes is developed in the paraelectric (hexagonal) phase, which is due to the lowest free surface energy of the (100) plane in the hexagonal phase. (2) The molecular chain motion in the paraelectric phase was revealed by X-ray diffraction and dielectric relaxation measurements : each chain molecule of TGTG' conformation undergoes the flip-flop motion and rotational motion independently of neighboring chain molecules in the hexagonal crystal, a crystal having liquid crystal characteristic. Based on these information we establish to a new concept to explain the anomalous dielectric properties appearing in the paraelectric phase. (3) The SC film is found to have very effective shear piezoelectricity. We developed transducers for transverse ultrasonic waves, which have been proved to be practically useful for non-destractive inspection of industrial materials. (4) The electrooptical property (Pockels effect) was measured. The result shows the film to be a potential material for electrooptical devices.In addition to the above mentioned results, we have obtained some useful and interesting results on the structure and properties of oriented films of (a) P(VDF/TrFE)/PMMA blends, (b) high pressure crystallized P(VDF/TrFE)/PVDF and (c) high pressure crystallized polyethylene. Less