Development of flexible organic materials with enhanced piezoelectricity

技术科学公司(TSI)生产各种无损检测产品，从单个传感器和接口模块到自动扫描系统以及完整的交钥匙检测和机器人系统。特别是，TSI生产了许多基于超声波和压电薄膜传感技术的专用系统。压电薄膜在包括超声换能器在内的各种传感器和致动器器件的开发中最近引起了相当大的关注。最简单的超声波传感器是单元件活塞传感器，其基于沿厚度方向沿着极化的压电板或圆盘。 多晶铁电陶瓷材料如锆钛酸铅（PZT）已成为换能器和阵列有源元件的主要材料。然而，铅的毒性引起了人们对PZT使用的担忧。对铅的含量进行了限制，并集中于最终消除其使用。此外，具有大约510 μm的晶粒尺寸的常规压电陶瓷并不特别适合于高频换能器应用。相比之下，已经发现压电聚合物如聚偏二氟乙烯（PVDF）及其与三氟乙烯（TrFE）的共聚物可用于生产高频换能器。 它们在传感应用中的优点包括良好的加工性、高柔性和顺应性、高电击穿场、重量轻和无毒。然而，压电聚合物与其陶瓷对应物相比显示出降低的压电性能。因此，TSI认为需要立即开发新的制造技术，以提高PVDF的压电性能，其共聚物（即，PVDF-TrFE）和/或其复合材料的性能达到与PZT相当或超过PZT的水平，而不损害PVDFs良好的可加工性、柔性和适形性。一种潜在的方法是促进结晶度并增强PVDF在超临界二氧化碳（ScCO 2）中从α到β形式晶体的相变，无论是否存在纳米填料作为成核剂。在 鉴于此，全面的研究目标是开发新的策略来微结构化PVDF膜，以增强其β相结晶，从而增强其压电性能。短期目标是：（i）阐明PVDF在其晶体结构背景下的加工与结构的关系;（ii）开发新的制造技术以增强PVDF中β晶体的形成;（iii）确定PVDF晶体结构对其压电性能的影响;以及（iv）通过定制其晶体结构来优化PVDF的压电性能。拟议的研究将为TSI提供指导方针，通过增加价值（例如，具有低成本和无毒的聚合物压电膜的超声换能器，所述聚合物压电膜具有良好的可加工性）。这将有助于TSI在超声波传感器技术的发展中处于领先地位，并将确保公司在全球传感器供应商中的领先地位。 总的来说，该项目中开发的数据和技术不仅将为压电PVDF基薄膜的设计和制造提供工艺指导，而且还为TSI改进其现有产品和新产品提供了新的机会。这些专业知识将有助于TSI展示其传感产品的优越性和环境可持续性。材料配方、加工技术和策略的开发将为TSI提供重要的方法、指南和数据，以促进柔性压电有机材料的开发。它还将协助技术支持系统客户改进和最大限度地提高其系统性能。

Techno Scientific Inc. (TSI) manufactures a wide range of non-destructive testing products from single transducers and interface modules to automated scanning systems as well as complete turnkey inspection and robotic systems. In particular, TSI produces a number of specialized systems based on ultrasonic and sensing technology with piezoelectric films. Piezoelectric films have recently attracted considerable attention in the development of various sensors and actuator devices including ultrasound transducers. The simplest ultrasonic transducer is a single-element piston transducer, which is based on a piezoelectric plate or disc poled along the thickness direction. Polycrystalline ferroelectric ceramic materials such as lead zirconate titanate (PZT) have been the dominant materials for the active elements of transducers and arrays. However, the toxicity of lead has raised concerns over the use of PZT. A restriction on the amount of lead present has been placed and is focused on eliminating its use eventually. Moreover, conventional piezoceramics, having grain sizes in the order of 510 µm, are not particularly suitable for high frequency transducer applications. In contrast, piezoelectric polymers such as polyvinylidene fluoride (PVDF) and its copolymer with trifluoroethylene (TrFE) have been found to be useful for producing high frequency transducers. Their advantages in sensing applications include their good processability, high flexibility and conformability, high electric breakdown field, light weight and nontoxicity. Nevertheless, piezoelectric polymers show reduced piezoelectric properties comparing to their ceramic counterparts. As a result, TSI sees promptly needs to develop new fabrication techniques to enhance the piezoelectric properties of PVDF, its copolymer (i.e., PVDF-TrFE), and/or its composites to the levels comparable to or exceeding those of PZT without compromising PVDFs good processability, flexibility and conformability. One potential approach would be to promote the crystallinity and to enhance the PVDFs phase transformation of a to beta-form crystal in supercritical carbon dioxide (ScCO2), either with or without the presence of nanofiller as nucleating agents. In light of this, the over-arching research goal is to develop novel strategies to microstructure PVDF films to enhance their beta-phase crystallization, and thereby their piezoelectric properties. The short-term objectives are: (i) elucidate the processing-to-structure relationship of PVDF in the context of its crystal structures; (ii) develop novel fabrication technologies to enhance the formation of beta crystal in PVDF; (iii) identify the effects of PVDFs crystal structures on its piezoelectric properties; and (iv) optimize the PVDFs piezoelectric properties by tailoring its crystal structures. The proposed research would provide guidelines for TSI to improve their current and future product lines by adding values (e.g., ultrasonic transducers with low cost and non-toxic polymeric piezoelectric films that have good processability). It would help TSI to spearhead in the development of ultrasonic transducer technology, and will secure the companys position at the forefront of sensors suppliers globally. Overall, the data and the technology to be developed in this project will not only provide processing guidelines for design and fabrication of piezoelectric PVDFbased films but also offer new opportunities for TSI to improve their current and new products. The know how will facilitate TSI to demonstrate the superiority and environmental sustainability of their sensing products. The material formulations, processing techniques and strategies to be developed will provide important methodologies, guidelines and data to TSI to facilitate the development of flexible piezoelectric organic material. It would also assist TSIs clients to improve and maximize their systems performances.