This chapter covers the main features and material examples of the electric field activated electroactive polymers. This class of electroactive polymers (EAPs) is very attractive in performing the energy conversion between the electric and mechanical form and hence can be utilized as both solid-state electromechanical actuators and motion sensors. As will be discussed in the chapter, the electromechanical response in this class of polymers can be linear such as in typical piezoelectric polymers or electrets, or nonlinear such as the electrostrictive polymers and Maxwell stress effect induced response.
Most of the piezoelectric polymers under investigation and in commercial use are based on poled ferroelectric polymers including PVDF-based and nylon-based ferroelectric polymers. This chapter will discuss in detail the properties of these ferroelectric polymers. In comparison with the electromechanical responses in inorganic materials, the electromechanical activity in these polymers is relatively low. In order to significantly improve the electromechanical properties in electric field activated EAPs, new avenues or approaches have to be explored. From the basic material consideration, these approaches include the strain change accompanied with the molecular conformation change, due to the polar vector reorientation, and from the Maxwell stress effect in soft polymer elastomers. This chapter will discuss the recent results based on those approaches, which have produced remarkable improvements in terms of the electric-field-induced strain level, elastic energy density, and electromechanical conversion efficiency in the electric field activated EAPs.
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