Abstract
Since the discovery of piezoelectricity in poly(vinylidene fluoride) (PVDF) 50 years ago, ferroelectric polymers have established their own areas for research and applications due to their unique properties in comparison to single crystals and inorganics. PVDF is a semicrystalline polymer that can crystallize into five different polymorphs. Among them, the polar β-phase is the most interesting one for electroactive properties because it has the highest dipolar moment and the highest piezoelectric response. In the early days, the β-PVDF was typically produced by melt processing, limiting its form to free-standing films. The rapid development of flexible electronics, however, highly requires β-PVDF fabricated from solutions under mild conditions. The objective of this perspective is to summarize the effective methods to produce β-PVDF from solution, to present the approaches for enhancing the electroactive properties through morphological controls, and to discuss the applications of PVDF-based ferroelectric polymers in flexible electronics. In addition, current challenges that may impede the further development of this field are pointed out.
Highlights
INTRODUCTIONSince the discovery of weak piezoelectric effects in bone by Fukada and Yasuda in 1957, researchers have begun to search for organic materials that might exhibit piezoelectricity. In 1969, Kawai found high piezoelectricity in stretched and poled poly(vinylidene fluoride) (PVDF) films. Subsequently, the piezoelectricity was found in some other synthetic polymers, such as polyurethanes, odd nylons, polyimides, polyureas, polylactic acids, etc. In the late 1970s, Kepler and Anderson confirmed the ferroelectricity in PVDF. Like many other ferroelectric materials, PVDF is pyroelectric, as revealed by Bergman and co-workers in 1971.9 The properties of polymers are so different in comparison to inorganics that they can fill the application fields where single crystals and ceramics are incapable of performing effectively. One common feature shared by polymers is the excellent mechanical property including high flexibility, low elastic stiffness, and high impact resistance
We briefly introduce the hierarchical structures of poly(vinylidene fluoride) (PVDF)
Much progress has been made in studying the fundamentals and exploring the applications of PVDF-based ferroelectric materials, the goal of comprehensive understanding and sustainability has not yet been achieved
Summary
Since the discovery of weak piezoelectric effects in bone by Fukada and Yasuda in 1957, researchers have begun to search for organic materials that might exhibit piezoelectricity. In 1969, Kawai found high piezoelectricity in stretched and poled poly(vinylidene fluoride) (PVDF) films. Subsequently, the piezoelectricity was found in some other synthetic polymers, such as polyurethanes, odd nylons, polyimides, polyureas, polylactic acids, etc. In the late 1970s, Kepler and Anderson confirmed the ferroelectricity in PVDF. Like many other ferroelectric materials, PVDF is pyroelectric, as revealed by Bergman and co-workers in 1971.9 The properties of polymers are so different in comparison to inorganics that they can fill the application fields where single crystals and ceramics are incapable of performing effectively. One common feature shared by polymers is the excellent mechanical property including high flexibility, low elastic stiffness, and high impact resistance. For some specific applications, the PVDF-based polymers are required to be in their electroactive (ferro-, piezo-, and pyroelectric) phases and be integrated on various substrates over large areas and threedimensional formats.16,31 It is sometimes necessary for the device to respond with a certain spatial and temporal resolution by patterning PVDF-based ferroelectric polymers into microscale or nanoscale. The morphology and structure can be tailored at the macroscale, microscale, or nanoscale In this perspective, we would briefly introduce the effective methods to produce β-PVDF from solution and the approaches for enhancing the electroactive properties through morphological controls and discuss the applications of PVDF-based ferroelectric polymers in flexible electronics. Current challenges that may impede the further development of this field are pointed out
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