Field-Activated Electroactive Polymers
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Zhongyang Cheng and Qiming Zhang Abstract Field-activated electroactive polymers (FEAPs) are a class of electroactive polymers that are insulating and exhibit coulombic interaction with and dipole formation in response to external electric signals. There are many polarization mechanisms in insulating polymers, from the molecular to the mesoscopic and even the macroscopic level, which couple strongly with mechanical deformation and can be used to create polymer actuators and sensors. FEAPs feature fast response speed limited by the polymer dielectric and elastic relaxation time, a very large strain level (to more than 100% strain), high electromechanical efficiency, the ability to operate down to micro/nanoelectromechanical devices, and a highly reproducible strain response under electric fields. One challenge in FEAP actuators and electromechanical devices is reducing the operation voltage to below 100 V or even 10 V while achieving an electromechanical conversion efficiency comparable with that of inorganic electroactive materials.
Introduction Among the electroactive polymers (EAPs) reviewed in this issue of MRS Bulletin, field-activated EAPs (FEAPs) are the most mature and are in use in a broad spectrum of industries. Applications include pressure/stress sensors in microphones and in automobile/highway condition monitoring; loudspeakers in audio systems; sonar transducers for underwater navigation; ultrasonic transducers for medical diagnosis and imaging; and nondestructive evaluation and monitoring of various civil, mechanical, and aerospace systems.1,2 FEAPs exhibit many characteristics favorable for electromechanical actuators and sensors, such as high flexibility, light weight, high stressimpact resistance, and easy processing. In the past 15 years, several discoveries and developments have led to great improvements in the electromechanical performance of FEAPs. For example, strain response, a key parameter for actuation application, is 2–3 orders of magnitude higher in the new FEAPs than in conventional piezoelectrics (~0.1%). Such a large strain with fast response time opens up new avenues for a broad range of technologies, especially artificial mus-
cles. Interestingly, most of these new EAPs are polymers used in daily life, such as insulators for electric cables and coatings on metal surfaces. One attractive feature of FEAPs is that their electromechanical response may originate from a change in chemical bonds and/or molecular configurations, making it possible to develop high-performance, electroactive micro/nanoscale and molecular devices. During the past several years, novel processing techniques have been developed for fabricating micro/ nanoscale EAP devices. In this article, the fundamentals and key characteristics of FEAPs as well the micro/nano processes and their capabilities are reviewed.
describe the coupling between the mechanical strain/stress (x/X) and the electric field/displacement (E/D) or polarization (P).3 ε0 is the vacuum dielectric permittivity. In the equations, the dielectric co
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