Piezoelectric PVDF Polymeric Films and Fibers: Polymorphisms, Measurements, and Applications

Abstract

The development of piezoelectric materials has surged forward due to their ability to convert mechanical energy into electrical energy and conversely. A wide range of materials have so far been introduced in the field, among which lead zirconate titanate (PZT) and polyvinylidene fluoride (PVDF) are the highlighted products because of their higher conversion efficiency, especially the high flexibility of the latter. PVDF is a semicrystalline polymer whose molecular structure is composed of a repeating monomer unit of (–CH2CF2–)n. In this chapter, different polymorphisms of PVDF depending on the chain conformations of trans (T) and gauche (G) linkages are presented. Also, various methods such as Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) analysis, and differential scanning calorimetry (DSC) employed for the investigation of phase transition are summarized. Strategies for the enhancement of the β-phase such as mechanical stretching, electrical polling, and addition of fillers are discussed. Moreover, the evaluation components of the piezoelectric efficiency including piezoelectric coefficients, responding voltage, polarization-electric field (P-E) hysteresis loops, electric displacement field (charge per unit area), permittivity (also known as dielectric constant), and dielectric loss factor (tan δ) are emphasized. Finally, the applications of PVDF polymers were discussed in the design of piezoelectric sensors, actuators, and energy harvesting devices.