Tuning the ferroelectric phase transition of PVDF by uniaxially stretching crosslinked PVDF films with CF-CH bonds

Poly(vinylidene fluoride) (PVDF) based relaxor ferroelectric polymers show great potential for applications in transducers, sensors and artificial muscles for their excellent electrostrictive properties. The all-transchain conformation of the current relaxor has to be stabilized by special monomers, such as trifluoroethylene or tetrafluoroethylene units, whose lower dipole moment than VDF leads to reduced dielectric and electrostrictive properties. Directly stretching the PVDF copolymers with bulky units, such as P(VDF-CTFE) and P(VDF-HFP) (CTFE and HFP refer to chlorotrifluoroethylene and hexafluoropropylene), has failed in fabricating PVDF relaxors for the too large steric hindrance of CTFE and HFP units. In the present work, we reported the special strategy of uniaxially stretching a family of PVDF polymers tailored by CF-CH bonds with smaller steric bulk to realize tunable ferroelectric performances for piezoelectric and electrostrictive applications. The pinning effect of CF-CH bonds on the crystalline phase of PVDF and the stretching induced chain conformation as well as ferroelectric phase transition are comprehensively disclosed. This work offers not only a fresh strategy for turning the ferroelectric performance of PVDF without the assistance of conformation stabilizing units, but also provides deeper insight into the understanding of the ferroelectric phase transition of PVDF.