Studies on Control of Higher Oder Structures of Ferrelectric Polymer Crystals and Their Applications

本研究的目的是为了进一步了解铁电聚合物的介电、力学和机电性能，通过控制铁电聚合物晶体的微结构来开发具有高温稳定性的高灵敏度压电聚合物，并为新型压电聚合物材料的应用奠定基础。主要研究材料为偏氟三氟乙烯共聚物[P(VDF/TrFE)]和聚偏氟乙烯(PVDF)。主要研究结果如下：1.研究发现，P(VDF/TrFE)单晶膜是由六方(顺电)相中的单轴拉伸薄膜晶化而成的，它由三个主轴上具有高度择优取向的全伸展链状晶体组成。通过在P(VDF/TrFE)的六方相中结晶，成功地制备了由完全伸展的链状晶体组成的P(VDF/TrFE)/PMMA共混膜。高度结晶的单晶…在高压下，六方相为热力学稳定状态的单轴链状聚乙烯结晶也形成了更多的类TAL薄膜。得到的薄膜是光学透明的，没有片状晶体。在较宽的温度范围内研究了P(VDF/TrFE)单晶薄膜的弹性、介电和压电性能。该薄膜具有迄今发现的最高的压电性。这些测量和X射线衍射研究揭示了铁电(R)相和顺电相中链分子在晶格中运动的详细信息。顺电相为液晶态。聚偏氟乙烯和高摩尔含量的聚偏氟乙烯和P(VDF/TrFE)在六方相下高压结晶，得到了β形的扩链晶体，该晶体在熔点(PVDF为205ﾟC)下表现出很强的压电效应。利用P(VDF/TrFE)的厚度剪切压电振动模式，研制了一种新型的横向超声波换能器。这些换能器的灵敏度可与陶瓷换能器相媲美。较少

This research project was performed for further understanding on dielectric, mechanical, and electromechanical properties of ferroelectric polymers, for development of piezoelectric polymers with high sensuitivity stable at high temperatures by controling micro-structures of ferroelectric polymer crystals, and for applications of newly developed piezoelectric polymer materials. The meterials mainly studied were vinylidene fluoride trifluoroethylene copolymers [P(VDF/TrFE)] and poly (vinylidene fluoride) (PVDF). The followings are the main results :1. P (VDF/TrFE) single crystaline films comprising fully extended chain crystals having highly preferential orientattion in three principal axs were found to be formed by crystallizing a uniaxilly stretched film in the hexagonal (paraelectric) phase.2. P (VDF/TrFE)/PMMA blend films composed of fully extended chain crystals were sucessfully obtained by the crystallization in the hexagonal phase of P (VDF/TrFE). Highly crystallized, single-crys … More tal-like films of polyethylene were also found to be formed by crystallization of uniaxially strethe film under high pressure where the hexagonal phase is thermodynamically stable state. The resulting film is optically transparent and includes no lamellar crystal.3. The elastic, dielectric, and piezoelectric properties of the single crystalline film of P (VDF/TrFE) were studied in a wide temperature range. The film has the highest piezoelectric activities ever found. These measurements and X-ray diffraction study revealed orecise information about the motions of chain molecules in crystal lattices both in ferroelect (R)^<^>c phase and paraelectric phaswe. The paraelectric phase is found to be a liquid crystalline state.4. High-pressure crystallization of PVDF and P (VDF/TrFE) with high molar content of VDF under the hexagonal phase yielded beta-form extended chain crystals which exhibit strong piezoelectric effects stable up to the melting points (205ﾟC for PVDF).5. Novel ultrasonic transducers for transverse ultrasonic waves were developed using thiekness shear piezoelectric vibration mode of P (VDF/TrFE). The sensitivity of these transducers were found very high comparable to that of ceramic transducers. Less