Studies on Growth and Properties of Large Single Crystals of Ferroelectric Polymers

以PVDF(聚偏氟乙烯)、P(VDF-TrFE)(VDF和三氟乙烯共聚物)、P(VDF-TeFE)(VDF和四氟乙烯共聚物)为原料，研究了铁电聚合物的结晶和性能，旨在获得大的单晶，阐明结晶机理，并将其应用于电子器件，特别是超声换能器。以下是本研究的主要结果。大单晶的生长：对P(VDF-TrFE)和P(VDF-TeFE)采用了不同的晶体生长方法。其中，高温高压晶化效果最好，所得单晶为厚约0.2微米、宽约10-100微米的片状晶体和直径约10-20微米的块状单晶。这些单晶是只在顺电或旋转相中生长的扩链晶体，在顺电或旋转相中，分子经历较大幅度的旋转振动。精确的相位…对于P(VDF-TrFE)，得到了更多随VDF含量变化的Se图。2.聚偏氟乙烯单晶：只有在2.4kb和230℃以上的高压和高温条件下才能生长出扩链的β-聚偏氟乙烯单晶，单晶表现出明显的铁电性和较强的压电性，可持续到205℃。因此，高压结晶聚偏氟乙烯薄膜是一种适用于压电聚合物中最高温度区域的薄膜。3.高温下的分子运动研究：通过宽线核磁共振、介电和力学测试，研究了P(VDF-TrFE)的结晶和居里转变过程中的分子运动。研究发现，在居里温度以上，链状分子沿分子链具有很强的流动性。4.在超声换能器中的应用：将高结晶度的P(VDF-TrFE)薄膜应用于各种超声换能器。结果表明，这些换能器可以在宽温度范围(4K-450K)和宽频率范围(5-1000 MHz)下工作。较少

Crystallization and properties of ferroelectric polymers were studied aiming to obtain large single crystals, to elucidate crystallization mechanisms, and to apply them to electronc devices, especially to ultrasonic transducers, using materials of PVDF (poly(vinylidene fluoride)), P(VDF-TrFE)(copolymers of VDF and trifluoroethylene), and P(VDF-TeFE)(copolymers of VDF and tetrafluoroethylene). The followings are the main results of the present studies.1. Growth of Large Single Crystals: Various methods for crystal growth were applied to P(VDF-TrFE) and P(VDF-TeFE). Among them, we found the crystallization under high pressures and high temperatures is most effective; the resulting single crystals were lamellar crystals about 0.2um thick and 10-100mum wide, and bulk single crystals with 10-20mum in diameter. These single crystals are extended chain crystals grown only in the paraelectric or rotational phase where the molecules undergo rotational vibration with large amplitude. Precise pha … More se diagram as a function of VDF content was obtained for P(VDF-TrFE). 2. Single Crystals of PVDF: Extended-chain beta-form single cystals of PVDF were grown only at high pressure and high temperatures above 2.4kb and 230 C. The single crystals exhibited conspicuous ferroelectricity and strong piezoelectricity which persist up to 205 C. Therefore, high-pressure crystallized PVDF film is usable at highest temperature region among piezoelectric polymers. 3. Studies on Molecular Motion at High Temperatures: The molecular motions correlating to crystallization and Curie transition were studied for P(VDF-TrFE) by means of broad line NMR and dielectric and mechanical measurements. It is found that chain molecules are very mobile along the molecular chains above the curie temperature. 4. Applications to Ultrasonic Transducers: Highly crystallized P(VDF-TrFE) films were applied to various ultrasonic transducers. It is found that these transducers can operate in the wide temperature range (4K-450K) and in the wide frequency range (5-1000MHz). Less