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

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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