Influence of HFP monomer segments on the crystal structure and electromechanical responses of a P(VDF-TrFE-CFE-HFP) tetrapolymer

The electromechanical properties of PVDF-based polymers, namely converting electrical into mechanical energy, are mainly decided by the crystal structure and domain size of the target product. Thus, we prepare the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), its terpolymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)), and tetrapolymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene -hexafluoropropylene) (P(VDF-TrFE-CFE-HFP)) films for comparison, respectively, where the role of the introduction of third and fourth monomers in the electromechanical properties of P(VDF-TrFE) is completely disclosed. Because of introducing CFE and HFP monomers, P(VDF-TrFE) with the ferroelectricity has converted into the relaxor ferroelectric P(VDF-TrFE-CFE-HFP) with a slimmer P-E loop while maintaining good maximum polarization (P_m). Since the nano ferroelectric domains in the relaxor ferroelectric material are easy to reverse along the polarizing electric field, The P(VDF-TrFE-CFE-HFP) sample achieved a dielectric constant (ε_r) of ∼29 and a strain in the thickness direction (S₃₃) of ∼ -5%, respectively, while the ε_r and S₃₃ of P(VDF-TrFE) sample are ∼11 and ∼-0.8 %, respectively. This research indicates the availability of the third and fourth monomers for improving the electromechanical effect of such electrostrictive polymers, having wide applications in flexible actuators, transformers, sensors, and so forth.