Enhanced Piezoelectricity from Highly Polarizable Oriented Amorphous Fractions in Biaxially Oriented Poly(vinylidene fluoride) with Pure β Crystals
Abstract Piezoelectric polymers hold great potential for various electromechanical applications, but only show low performance, with |d33| < 30 pC/N. We prepared a highly piezoelectric polymer (d33 = -62 pC/N) based on a biaxially oriented poly(vinylidene fluoride) (BOPVDF, crystallinity = 0.52). After unidirectional poling, macroscopically aligned samples with pure β crystals were achieved, which showed an unprecedentedly high spontaneous polarization (Ps) of 140 mC/m2. Given the theoretical limit of Ps = 188 mC/m2 for the neat b crystal, the high Ps could not be explained by a simple two-phase model (i.e., the crystalline and the amorphous phases). Instead, we deduce that a significant amount (at least 0.25) of an oriented amorphous fraction (OAF) must be present between these two phases. Experimental data suggest that the mobile OAF resulted in the negative and high d33 for the poled BOPVDF. The plausibility of this conclusion was supported by molecular dynamics simulations.