Process induced electroactive β-polymorph in PVDF: effect on dielectric and ferroelectric properties.

The effects of various processing conditions, like annealing, poling, mechanical rolling and their combinations, on the dielectric and ferroelectric properties of PVDF [poly(vinylidene fluoride)] were systematically studied in this work. Further, the effect of processing sequence on the structure and properties was investigated. While all the processing conditions adopted here resulted in phase transformation of the α- to electroactive β-polymorph in PVDF, the fraction of β-phase developed was observed to be strongly contingent on the adopted process. The transformation of α to electroactive β-polymorph was determined by X-ray diffraction and FTIR. The neat PVDF showed only α-phase, whereas mechanically rolled samples exhibited the highest ca. 85% β-phase in PVDF. Both the permittivity and the loss tangent decreased in the samples which had undergone different processing conditions. The polarization-electric field (P-E) loops for all the samples were evaluated. Interestingly, the energy density, estimated from the electrical displacement-electric field (D-E) loops, was observed to be highest for the poled samples which were initially rolled. The results indicate that various processing conditions can influence the dielectric and the ferroelectric properties differently.