Ferroelectric polymers as multifunctional electroactive materials: recent advances, potential, and challenges
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Polymers/Soft Matter Prospective Article
Ferroelectric polymers as multifunctional electroactive materials: recent advances, potential, and challenges Xiaoshi Qian, Shan Wu, Eugene Furman, and Q.M. Zhang, Department of Electrical Engineering and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA Ji Su, NASA Langley Research Center, Hampton, Virginia 23681, USA Address all correspondence Xiaoshi Qian, Q. M. Zhang at [email protected]; [email protected] (Received 23 February 2015; accepted 14 April 2015)
Abstract As multifunctional electroactive materials, ferroelectric polymers are unique owing to their exceptionally high dielectric strength (>600 MV/m), high flexibility, and easy and low-temperature fabrication into required shapes. Although polyvinylidene difluoride (PVDF)-based ferroelectric polymers have been known for several decades, recent findings reveal the potential of this class of electroactive polymers (EAPs) to achieve giant electroactive responses by tuning the molecular, nano, and meso-structures. This paper presents these advances, including giant electrocaloric effect, giant electroactuation, and large, hysteresis-free polarization response. New developments in materials benefit applications, such as environmentally benign and potentially highly energy-efficient electrical field controlled solid-state refrigeration, artificial muscles, and high-energy and power density electric energy storage devices. The challenges in developing these materials to realize these applications, and strategies to further improve the responses of EAPs will be also discussed.
Introduction Ferroelectricity was first observed in inorganics (Rochelle salt) by Valasek in 1920.[1] After the humble beginnings extending approximately to the World War II, when only a handful of ferroelectrics were known, there was an explosion of new materials and applications first in inorganic and later polymeric materials. Interests in these materials have not abated, and several major areas of their usage are outlined in this paper which emphasizes recent developments in ferroelectric polymers for energy storage, cooling, and artificial muscles. The intrinsic symmetry of the ferroelectric material enables not only ferroelectricity, which is associated with a spontaneous electric polarization in a material that can be switched by an electric field, but also coexisting piezoelectricity and pyroelectricity, which are the electro-mechanical energy conversion and electrothermal energy conversion processes, respectively, as is illustrated in Fig. 1(a). Ferroelectricity in polymers was discovered much later in 1970s in the polyvinylidene difluoride (PVDF) homopolymer and later in PVDF-based copolymers such as P(VDF–TrFE) [TrFE, (trifluoroethylene)].[2] These multifunctional electroactive polymers (EAPs),[3] which are flexible and lightweight, and can be easily processed into different shapes by room temperature (RT) or low-temperature fabrication methods, have attracted a great deal of public attention and been e
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