Effects of annealing on the polarization switching of phase I poly(vinylidene fluoride)

Abstract

AbstractTo obtain information about microscopic processes involved in the polarization switching in uniaxially oriented poly (vinylidene fluoride) film, a least‐squares estimation of nonlinear parameters was developed to yield parameters of an equation which describes the nucleation and domain growth process. Time domain measurements of polarization reversal revealed that switching times decreased as the annealing temperature Ta increased (67.0, 52.4, and 41.3 μs at –20°C under a 200 MV/m pulse field for the as‐stretched samples, the samples being annealed at 120 and 160°C, respectively). The analysis showed that the value of the domain growth speed increased as Ta increased. This is consistent with x‐ray diffraction data which indicated that the annealing process brought about better chain packing and increased crystallite perfection. The analysis also showed that the nucleation probability significantly increased as Ta increased. This result was interpreted in terms of a morphological transformation, which was indicated by the decrease in elastic modulus with increasing Ta with no corresponding loss of orientation. It is suggested that the annealing process brought about an increase in the number of nucleation sites as a result of a transformation from a fibrous structure to a crystal‐amorphous series structure which has increased boundary zone area.