Magnetic field induced formation of ferroelectric β phase of poly (vinylidene fluoride)

The poly (vinylidene fluoride) PVDF have been fabricated at magnetic fields H of 0, 1, 3, 6 T, respectively. The structure analysis revealed that the PVDF prepared at zero (i.e., H = 0 T) and high magnetic fields (i.e., H = 1, 3 and 6 T) shows a coexistence of γ and α phases and coexistence of β and α phases, respectively. The highest calculated content of the β phase is ~ 40% for all the samples prepared under different magnetic fields. The magnetic field induced tensile stress on the diamagnetic PVDF as revealed by the magnetostriction experiments is suggested to result in the formation of the β phase. The differential scanning calorimetry (DSC) results showed a first increase and then decrease in the crystallinity with increasing strength of magnetic fields. Detailed analysis of the magnetostriction and DSC results shows that the magnetic field effect on the formation of the β phase can be ascribed to the competing effects of tensile strain and crystallization inhibition induced by magnetic fields. Our results suggest a new route to obtain the β phase PVDF for potential practical application.