Development of flexible organic materials with enhanced piezoelectricity

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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.