Research On The Piezoelectricity Of PVDF-HFP Based Composites

Compared to the most commonly used piezoelectric material PZT (Lead Zirconate Titanate), PVDF (Poly (vinylidene fluoride)) and its copolymers are promising candidates due to their non-toxicity, recyclability, high resistance to halogen and acid and fatigue, thus it is of great importance in the field of energy harvesting. Moreover, as it is flexible, it can be shaped in any forms and applied to any type of structures. The piezoelectricity of PVDF and its copolymers is mainly determined by the fraction of β-pahse and its direction of dipole. As a result, the phase transformation from α toβ phase stands in the focus of research.In this study, we added five kinds of nanofiller, i.e., MWNT (Multi-walled carbon nanotube), VGCF (Vapor grown carbon nanofiber), rGO (Reduced graphene oxide), CB (Carbon black) and AgNW (Silver nanowire), to prepare PVDF-HFP based piezoelectric composite films. The preparation process was developed and the effects of nanofiller addition, stretching and poling were investigated.By this study, we came to the following achievements:(1) High piezoelectric PVDF-HFP composites were prepare by addition of various nanofillers (MWNT, VGCF, rGO, CB, AgNW); A preparation process was developed and the parameters such as curing temperature, elongation ratio, temperature for stretching, stretching speed and electric field for poling were determined.(2) A measurement set up for evaluating the open circuit voltage and the power harvesting was built, it includes signal generator, amplifier, electric magnet, A1 plate fixed unit, displacement meter and oscilloscope;(3) The crystal structure was investigated by FTIR and XRD to declare the influences of addition of nanofillers, stretching and poling and the transformation in the three stages. SEM and POM were used to observe the morphology and the dispersion of nanofillers in the composites and DSC was used to determine the degree of crystallinity of composites;(4) AgNWs saved in ethanol was transferred to DMF by solution displacement method to prepare PVDF-HFP/AgNWs composites by melt solution method, it avoided the bubbles in the direct use of AgNW/ethanol solution.