Effect of drawing on the dielectric properties and polarization of pressed solution cast β-PVDF films

Poly(vinylidene fluoride), PVDF, samples containing exclusively the polar beta phase were obtained by crystallization from N,N-dimethylformamide (DMF) solution at 60 degrees C and subsequent pressing. Some of these samples were uniaxially drawn at 120 degrees C at draw ratio of 4, resulting in oriented films. Oriented and unoriented samples were characterized as to relative fraction of beta phase, degree of crystallinity and orientation by infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). The dependence on frequency of the real (e(Gamma)') and imaginary (epsilon('')(Gamma)) components of the relative permittivity of the samples was determined between 10(4) and 1.7(9) x 10(7) Hz. The coercive field and stable and metastable remanent ferroelectric polarization were determined from the hysteresis loop obtained by the ramp voltage technique, described in detail in this work. The results allowed verification of the effect of drawing on structure and of the resulting structure on the dielectric properties, remanent polarization, and coercive field of beta-PVDF. A possible effect of the crystal-amorphous interphase region on the metastable remanent polarization is suggested. The results obtained with the oriented and unoriented samples were compared with those obtained for films commercialized by Piezotech S. A.