Advances in copolymers based on polyvinylidene fluoride (PVDF) and their composites for piezoelectric energy harvesting

Polyvinylidene fluoride (PVDF) is among the most promising piezoelectric polymers due to its attractive properties such as piezoelectricity, light weight, high flexibility, thermal stability and chemical resistance. The polymer has potential for harvesting of ambient energy and the associated secondary applications. This review discusses the potentials of PVDF and its copolymers and composites consisting of a variety of fillers such as metal oxides, organic/inorganic lead halides and carbon based nanofillers. A summary of recent advancements in materials development, processing, and applications is presented, along with a discussion of the challenges and future outlook. Enhancement of crystallinity and β–phase formation, hence the piezoelectricity in PVDF-based materials is discussed in detail. Also covered is the use of computational methods in understanding of the processing-structure-property relations in PVDF-based materials – density functional theory (DFT), molecular dynamics (MD), finite element analysis (FEA) and phase field method (PFM). Despite the progress made in improving the piezoelectric properties of PVDF-based materials, the piezoelectric properties are still low. The highest piezoelectric constant that has been achieved so far for PVDF is 30 pC/N, relative to 550 pC/N for PZT. Efforts are still needed to improve the piezoresponse of these flexible piezoelectric polymers for energy harvesting, particularly for environmental monitoring as well as the wearable and implantable devices.